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Immature scape of Rocambole garlic 'Spanish Roja' goes for the double loop. Carl Rosen
Porcelain garlic 'Music' forms a pretzel-scape. Carl Rosen
Flower stalks that do loop-de-loops or look like pretzels??
Fall-planted hardneck garlic can produce scapes (flower stalks) that coil and bend in curious ways. The scapes normally appear in mid-June and the shapes they form at this stage are often a distinguishing feature of the variety. For example, the Rocambole variety typically has one to three uniform coils (top photo shows the Rocambole strain ‘Spanish Roja’). The Porcelain variety has more random type coils, some of which may take the shape of a pretzel (bottom photo shows the popular Porcelain strain ‘Music’). In both varieties, the coils straighten out as the scapes mature.
Most garlic growers cut the scapes before they mature. Removing the scapes at the immature stage allows the bulb to grow larger because photosynthate that would have gone to the scape will be redirected to the bulb. Another reason why growers cut the scapes when they are immature is that they are edible and often sought after by gourmet chefs. Scapes can be cut into 1 to 2 inch long pieces and steamed as you would green beans or asparagus. They can also be pickled or used in stir fries. Don’t eat the scapes once they mature, though -- they become very woody and tough.
Another unusual characteristic of these garlic scapes is that the flowers rarely develop. If flowers do appear, they’re usually sterile. Instead of flowers, the garlic plant will produce bulbils (very small garlic cloves). These bulbils are genetically the same as the mother plant. They can be eaten as normal garlic or planted in the garden to produce small bulbs for the following year.
Some varieties of garlic have lost the capacity to produce a flower stalk. These are called softneck varieties and are the most common types found in supermarkets. Most locally grown garlic is of the hardneck type and will produce scapes. For more information, see Growing Garlic in Minnesota. -Carl Rosen, Professor and Extension Soil Scientist
Many people have heard of Dutch elm disease. Some may even remember neighborhood streets and parks that were suddenly exposed to the sun by the loss of the large elm trees that previously sheltered them. Unfortunately Dutch elm disease is as serious today as it was in the early 1930s when the fungus that causes this disease was first introduced to North America.
Figure 1: Two trees suffering from Dutch elm disease. Michelle Grabowski
Ophiostoma ulmi is the fungus that first started the Dutch elm disease epidemic in North America. This fungus originated in Asia, made its way to Europe (where it picked up the name “Dutch” elm disease) and finally arrived in North America. O. ulmi was later replaced by a more aggressive relative, Ophiostoma novo-ulmi, which is the main pathogen associated with Dutch elm disease in North America today.
American elms (Ulmus americana) are highly susceptible to the Dutch elm disease fungus. The fungus infects the vascular system of the tree, blocking the flow of water from the roots, resulting in wilted leaves and eventually death of the tree. Trees can become infected in two ways:
Identifying Dutch elm disease
Figure 2: Discoloration of wood in branches infected by Dutch elm disease. Michelle Grabowski
American elms should be monitored throughout the growing season for symptoms of Dutch elm disease. Infected trees will first show one to a few “flagging” branches. These branches will have wilted and yellow leaves that will eventually die and turn brown, but remain attached to the tree. For a positive diagnosis, 4 to 6 branch segments that are approximately 6 to 8 inches long and ½ to 1 inch in diameter should be cut from a symptomatic branch, sealed in a zippered plastic bag, and sent to the University of Minnesota Plant Disease Clinic. The branch segments should still be moist (not dead and dry), need to be refrigerated until sent to the clinic, and should be brought directly to the clinic or mailed overnight. These branches will be tested for the presence of O. novo-ulmi and results of the test will be available in 2 to 3 weeks.
Pruning out the Infection
It is possible to prune out diseased branches and stop Dutch elm disease from spreading deeper into the tree if the infection is caught early enough. The infection causes visible brown staining of the sapwood that can be seen if the bark is peeled off infected branches. The fungus is actually deeper in the tree than the staining indicates and the branch must therefore be cut 10 feet from where the last sign of staining can be seen. This will remove the fungus from the tree, but new infections may occur at a later time. (Fig 2)
Preventative Treatments
The best way to prevent Dutch elm disease in American elms is to protect them with preventative fungicides. Trees are treated in a process called macro infusion. Small holes are drilled in the root flare (the widening base of the trunk) of the tree. Plastic tees and tubing are used to carry the protective fungicide to these holes and into the tree’s vascular system. One macro infusion treatment will protect a tree for one to two years depending on which fungicide is used. Macro infusion treatments can protect a tree from spores transmitted by beetles, but do not protect against infection through a root graft. Although macro infusion treatments will not cure a severely infected tree, they can be used in combination with pruning of infected branches to save a recently infected tree. These treatments should only be done by a certified arborist.
Sanitation to Save Trees
As unlikely as it seems, removing severely diseased trees and properly disposing of diseased wood is one of the most important control strategies available. Many people do not realize the Dutch elm disease fungus continues to grow and survive in their tree even after it has been killed. Elm bark beetles will be attracted to these dead trees as well as to trees dying from the disease. If these trees are not cut down, they become breeding grounds for both the fungus and the beetles, resulting in a dramatic increase in Dutch elm disease in the area.
If a tree is infected by Dutch elm disease to the extent that more than a few removable branches are infected, the entire tree should be removed as soon as possible. Once cut down, wood from the diseased tree must be debarked, burned, buried, or cut into woodchips. Logs with bark that are left for firewood or other uses will continue to support both the fungus and the elm bark beetle, and will therefore continue to add to the disease epidemic.
Unfortunately many elms killed by Dutch elm disease in the United States today are not properly cut down and disposed of. Because of this neglect the elm bark beetle population has been able to grow and Dutch elm disease has continued to spread.
A Case Study in the Success of Sanitation
Figure 3: Healthy American elms in Joan of Arc Park, Quebec City, Canada. Michelle Grabowski
In a recent trip to Quebec City, Canada, I visited Joan of Arc Garden. This beautiful park is sheltered by the graceful arching branches from several long rows of mature American elms. This park exists because Quebec City has an amazing program to control Dutch elm disease. No fungicides are used in this program. Instead each year all of the elms in the city are monitored for Dutch elm disease symptoms. Infected branches are quickly cut off and properly disposed of. If a tree has more than 5% of its canopy infected it is considered too far gone, and is cut down. The wood is properly disposed of. With the surrounding suburbs participating in this program, very few infected trees are left standing. Therefore there are very few beetles carrying the fungus to start new infections. As a result only a few trees are lost each year, and each year more American elms are planted to replace them. 10,000 healthy American elms live in Quebec City today. (Fig 3)
American Elms in America’s Future
Possibly the best hope for a future of healthy elms in America is the development of disease resistant cultivars and hybrids. For years scientists have worked to screen American elms for individuals that are resistant to Dutch elm disease. At the same time crosses among the more resistant Asian elm species were made in the hope of finding a tree that looked like the American elm but carried the disease resistance of its Asian relative. There are several Dutch elm disease resistant elms available today. Many of them are hardy and will grow well here in Minnesota. None of these trees is completely immune to the disease, rather, they are considered highly resistant. If infected with Dutch elm disease, these trees may show some wilting or leaf discoloration but are able to recover and continue to grow. Many of these elms have already been planted in Minnesota and across the United States. (read the next article for more information on these elms)
Photo 1. An 8 year old Accolade™ hybrid elm. Chad Giblin
Photo 2. Accolade™ elm after about 15 to 20 years of growth. Chad Giblin
Whether you live in the Twin Cities, out in the country, or in any one of Minnesota’s many communities, it’s hard not to notice native American elms falling prey to Dutch Elm Disease (DED). Fortunately, since the 1970s, dedicated researchers have been working to breed and select DED-resistant trees to replace those stately giants. Now, more than ever, these trees are finding their way into home landscapes due to increased demand and availability through retail outlets.
Since 1999, the Teaching, Research, and Extension (TRE) Nursery on the University of Minnesota’s St. Paul Agricultural Experiment Station has been cooperating with the Minneapolis Park and Recreation Board’s Forestry Division to evaluate and select elms for use in Minnesota. To date, we have worked with more than 1,000 elm trees selected from over 25 different varieties. Many of these varieties are now readily available, while others are still being evaluated and may be hard to find at nurseries.
Here are some of the DED-resistant elm selections we’ve evaluated that should be fairly easy to find at your local garden center, retail nursery, or via mail order. Unless stated differently, all trees listed below should be hardy in USDA Hardiness Zone 4.
Accolade™ – Hybrid Asian Elm
The Accolade™ elm has a mature form that is similar to the American elm, but is slightly more upright and a bit smaller. Photo 1 shows an Accolade™ that is about 8 years old, slightly larger than most trees currently sold in retail garden centers. In Photo 2 we see another Accolade™ elm after about 15 to 20 years of growth. Accolade™ has shown excellent performance in winter hardiness tests in the Twin Cities area and generally outperforms many other varieties in terms of insect resistance. In 2004 we discovered two Accolade™ elms that had DED. One of the two trees, currently under observation at the U of MN, currently has no remaining symptoms of the disease. While it was disconcerting to see DED symptoms on this elm, it was a good reminder of what the term “resistant” means. None of these selections is “immune” to the disease.
Photo 3. This ‘Cathedral’ elm is about 30 years old. Chad Giblin
Photo 4. ‘Discovery’ elm is Zone 3 hardy and drought tolerant. Chad Giblin
‘Cathedral’ – Hybrid Asian Elm
‘Cathedral’ is another long-time favorite introduced by the University of Wisconsin. Due to its vaselike form in the nursery, this variety was selected by the University of Minnesota to replace American elms lost on the Northrop Mall on the Minneapolis Campus. Photo 3 shows a ‘Cathedral’ elm about 30 years after planting. This tree is a little stunted because it’s actually growing on an old road bed! In better soil conditions, you could expect up to twice as much growth. In addition, ‘Cathedral’ has good resistance to elm leaf beetle and other leaf-chewing insects. Unfortunately, it appears to be a favored food source for leaf hoppers and similar pests so some insect control may be necessary.
‘Discovery’ – Asian Elm
Like Accolade™, the ‘Discovery’ elm has leaves that are much smaller than the American elm. It is slower growing than other elms, so maintenance is a little easier. Even with the slower growth, this selection requires a fair amount of crown thinning as a young tree to avoid crossing branches. Some sources suggest its ultimate form may be vaselike, but in nursery evaluations at the U of MN it has been fairly upright (Photo 4). This tree has been extremely hardy in St. Paul, and there are a number of these already growing in the Minneapolis Parks system. ‘Discovery’ is one of the most stress- and drought-tolerant hybrid elms available and is the best choice for those living further north, as it is reliably hardy into USDA Hardiness Zone 3.
‘Princeton’ – American Elm
‘Princeton’ is a true American elm that was actually selected in 1922 for “superior horticultural qualities” just prior to the DED epidemic! This year, ‘Princeton’ is getting some well-deserved national attention due to its superior DED resistance. Unfortunately, some news agencies are reporting this to be a new American elm selection, causing confusion for gardeners trying to find the “new” ‘Princeton’ elms. This is the same ‘Princeton’ that has been around for 85 years! This tree is slightly more upright than many of the seedling American elms around, which is both beneficial and challenging in terms of maintenance. This selection has had a little trouble with winter tip dieback, but outside of the nursery setting this seems to be less of a problem, especially under lower fertility conditions. The ‘Princeton’ elm was selected for the World War II memorial on the south lawn of the Minnesota State Capitol grounds (Photo 6).
American Liberty – American Elm
The American Liberty elm is a patented selection currently grown only by the Elm Research Institute in New Hampshire. This tree is a “multi-clone” which means that there are actually six different genetically unique clones that are sold under the American Liberty name. Growth rate for American Liberty is quite variable, depending on the clone you receive, but in general expect 3 to 6 feet of growth per year once established. Do a web search for “American Liberty elm” and you should be able to find all the details necessary to order this tree through the mail.
Maintenance
Many of these elms require considerably more pruning and training than many of the more common landscape trees. This problem can be exacerbated under high fertility conditions, which is often the case in home lawns. The first ten years of a tree’s life often determines how it will perform for the remainder. In the case of elms, a small investment in maintenance during the “formative years” will have a huge payoff when it is approaching maturity.
Photo 5. Elm-planting techniques were a bit different in 1912!
Photo 6. ‘Princeton’ elms planted near the WW II memorial at the Minnesota State Capitol. Chad Giblin
In the past, elm maintenance and pruning became almost a fine art. With time however, research, public perception and consumer demands changed how we produced and planted trees. Photo 5 was taken in 1912 and shows a typical American elm being planted on the U of MN St. Paul Campus. (Note: Today, we’d never remove so much of the top or plant so deeply!) In Photo 6 we see a newly-planted ‘Princeton’ elm in the form sold at most nurseries today. These trees are the products of both different generations and maintenance regimes. Both trees are doing fine, but require drastically different types of care.
Like most trees, American and hybrid elms are best maintained with a strong central leader. This means that you should see a fairly strong, columnar stem reaching to the top of the tree. As the lower side branches grow and increase in diameter, they need to be removed until the desired height clearance for the site is reached. In the case of city boulevards this is often to a height of 15 feet or more to accomodate passing trucks. If the tree is on residential or commercial property away from streets, branches may only need to clear about 8 to 10 feet.
In some cases, elms will need to be pruned two or more times a year, even during the growing season. In addition to pruning, elms may also require staking and splinting, especially for strong central leaders. This assures a straight stem and keeps the tree growing up rather than out! Knowing when and how much to prune as well as other training techniques requires experience, so if you’re not sure how to work on young trees be sure to contact an ISA Certified Arborist to get you started right. The investment made now will really pay off when your tree is growing beautifully and providing shade on your property.
Finally, be sure to ask your local garden center or nursery to find these elms for you if they don’t stock them already. The demand for these trees is growing because consumers are looking for them. Ask about other elms that you may have heard about, and encourage them to special order trees, if that is possible. We will never return to the “good old days” when all the streets were lined with American elm trees, but having this group of DED resistant elms to add to our “Tough Trees” list makes our communities greener and cooler!
For more information on the TRE Nursery see: www.tre.umn.edu
Whitelined sphinx caterpillar on evening primrose. source unknown
Whitelined sphinx caterpillars were recently reported from two sites in central Minnesota (you can find this insect throughout Minnesota). In both cases they were feeding on evening primrose. They are also reported in the literature to feed on grape plants, plants in the Rosaceae (rose family), and many types of herbs and woody plants. They apparently feed June through July.
This insect grows as large as three inches long. You can identify it as a sphinx caterpillar by the distinctive horn or tail on the end of its body. The color of whitelined sphinx caterpillars is variable. Most are green with black stripes and yellow and orange markings, although some are mostly black with some greenish yellow. This insect turns into an attractive moth which can be seen visiting flowers at dusk in August and September. Because of its rapid wingbeats and darting motions it is often mistaken for a hummingbird.
In most cases, you can ignore whitelined sphinx caterpillars in your garden. If they are causing more damage than you wish to tolerate, try to move them to an alternative food source (you will have to experiment to see what they like). If that is too much effort, than just handpick them and throw them into a bucket of soapy water. You should not need insecticides to deal with these caterpillars.
Apple curculio. Jeff Hahn
An interesting and uncommon pest of apples was found recently in Douglas and Stearns counties. The apple curculio, Anthonomus quadrigibbus, a type of weevil, is related to plum curculio which is a common pest of apples. These two weevils are similar in size (about 1/4 inch long) and both have four bumps on their backs. However an apple curculio is reddish brown and has a longer and more slender snout while a plum curculio is darker colored with a shorter, stockier snout.
The apple curculio overwinters as an adult in debris on the ground. It moves to apples in the spring and damages developing apples by making small punctures as it feeds and oviposits. This damage can also cause the apple to become lumpy and misshappen. The oviposition punctures, unlike plum curculio, are small and round and not crescent-shaped. The larvae do not survive in developing apples; they can only finish their life cycle when the fruit drops prematurely. Apple curculio also develops on crabapple, juneberry (Amelanchier), and hawthorn.
Currently there are no management tactics for this insect. It is also not clear how widespread this insect is or how abundant it may become in an orchard. This has always been an uncommon insect that people did not need to worry about. However, if that is going to change, it would be good to know. It would be helpful to learn more about where this insect has been found in Minnesota and the amount of damage it is causing. If you discover this insect and its damage, please contact the author with information about its location.
Pavement ant swarmers. Jeff Hahn
Winged ants are the reproductive members of a colony, that is, they are fertile females and males (workers are sterile females). They fly out of the nest, usually males first followed by the females, to mate. The newly mated females (queens) fly off to search for a place to start a new nest. Different ant species swarm at different times of the year.
Pavement ants swarm from May through July. The females are about 1/4 inch long, reddish brown to black, and have a normal-sized head. The males are a little smaller and possess a smaller-sized head (sorry guys). If you look closely at either of them, you can see they have a two-segmented node.
There have been several cases recently of winged pavement ants being found indoors. Despite the circumstantial evidence, when they fly out from behind a baseboard or a false ceiling, they are not nesting there. Pavement ants nest in the soil under some kind of cover, like stones, bricks, wood, sidewalks, and driveways. When you find them indoors, they are most likely nesting under the concrete slab. As they leave the nest, they may find their way into heat ducts or wall voids and emerge from different sites in homes.
When you see winged ants, they are not a threat to people or property but they can be a nuisance, especially since a pavement ant swarm can continue for one to two weeks. The best short-term control is to physically remove the ants, such as with a vacuum cleaner. However, you could possibly see a swarm again the following year. If you can detect where the ants are emerging, you may be able to prevent future problems by sealing that space
If you are interested in long-term control and don’t want to have to deal with these swarms at all, you will have to eliminate the nest, the source of the swarmers. However, this is easier said than done. Because the nest is concealed under the concrete slab, it is difficult to directly treat it. People might be tempted to try to bait the swarmers but because these ants do not return to their nest, this method is not effective. You can, however, bait workers when they are present. This may be more likely during winter as workers usually spend most of their time outdoors during summer as they forage. Use a bait effective against grease-feeding ants and place the product where the ants are active.
You may also consider hiring a professional pest control service. If they can detect where the ants are coming up through the concrete slab, e.g. through an expansion joint, they can dust and seal the area which should effectively take care of the problem. They are also experienced at baiting ants.
The 16 Essential Elements Plants Need to Grow
Macronutrients Nitrogen (N), Phosphorous (P), Potassium (K), Carbon (C), Hydrogen (H), and Oxygen (O)
Secondary nutrients Calcium (Ca), Sulfur (S), and Magnesium (Mg)
Micronutrients Iron (Fe), Manganese (Mn), Molybdenum (Mo), Chlorine (Cl), Boron (B), Copper (Cu), and Zinc (Zn)
Iron is one of the 16 essential elements that plants need to grow. They get these elements from molecules in the air (oxygen and carbon dioxide gases) and as ions (electrically charged particles) dissolved in water within the soil. Lacking sufficient quantities of even one of these essential elements can cause a plant to decline and eventually die. Essential elements are divided into three groups based on the relative quantity of each that is needed- macronutrients, secondary nutrients, and micronutrients (see sidebar for details). Macronutrients are needed in the greatest relative quantity and micronutrients (like iron) are needed in the smallest relative quantity.
Iron deficiency symptoms can appear quickly because iron is involved with chlorophyll and photosynthesis. Iron is important for the synthesis of chlorophyll and chloroplasts, the structure chlorophyll is housed in. However, iron is not integrated within the chlorophyll molecule itself. The end result of deficient levels of iron is reduced chlorophyll. Chlorophyll is a pigment that provides plants with their green color and is essential for photosynthesis. Without chlorophyll plants cannot capture energy from light to fuel their growth and development.
Chlorosis or yellowing of foliage is the key symptom indicating that plants have a relatively low concentration of chlorophyll. Chlorosis can be caused by a number of things including nutrient deficiencies other than iron as well as herbicides, so it is important to be aware of unique chlorosis patterns so the appropriate cause and then course of action can be determined. Fortunately there are some chlorosis patterns unique to iron deficiency to watch for as well as some indicator plants in our landscapes that we can especially keep an eye on.
Iron chlorosis on Carefree Delight shrub rose. David Zlesak
Iron chlorosis (and some powdery mildew) on Foxi Pavement rugosa rose. David Zlesak
Symptoms of iron deficiency:
Determining the cause(s) of iron deficiency
In order to alleviate iron deficiency it is important to understand the reason(s) why there are not adequate levels of iron so an appropriate course of action can be taken. Potential causes include:
The most common cause of iron chlorosis for gardeners is high soil pH (usually above 7.0). The pH of the soil affects solubility and therefore the availability of elements to enter into solution and be available to plant roots. The metal essential elements, like iron, are more soluble in water and available to plants as the pH decreases (becomes more acidic), while other elements like calcium and magnesium are more soluble and available to plants at a higher pH.
Swamp white oak foliage shows advanced stages of iron chlorosis. David Zlesak
If your plants show symptoms of iron chlorosis, one of the best things to do is get the soil tested. A professional soil test can tell you the soil pH, nutrient levels, and soil texture. If pH presents itself as the main interference to iron availability, the current pH and soil texture are both important pieces of data to calculate how much and of what to add to the soil to adjust the pH to within a suitable range. In addition, learning the status of key essential elements in the soil will be helpful to know if iron truly is deficient or if other elements are overabundant and are interfering with iron uptake. (For information on soil testing: http://soiltest.coafes.umn.edu/)
Some plants are naturally more susceptible to iron chlorosis than others and can serve as indicator plants for iron deficiency in the soil or lack of iron availability. Plants that are adapted to acidic soils tend to have a greater need or tolerance to iron. Once such species are planted in soils with a higher pH than what they are adapted to, many have difficulty acquiring enough iron. Acid-loving plants that readily show iron chlorosis symptoms include many Ericaceae family (heath family) members like blueberries, azaleas, and rhododendrons, trees like pin oak and river birch, and annuals like petunia and bacopa.
Some plants with an especially high iron requirement have developed ways to better extract iron from the soil and then utilize it within their tissue. Some iron loving plants exude special organic molecules (in chemistry organic simply means containing carbon). These organic molecules act as a chelating agent (chele=claw), holding onto or capturing iron and then readily releasing it to the plant.
River birch with iron chlorosis - symptoms most noticeable on right trunk. David Zlesak
How to alleviate iron deficiency
Will foliar fertilizing really make your garden grow? Nancy Rose
Foliar fertilizers are dilute fertilizer solutions applied directly to plant leaves. As with soil application of fertilizer, the goal of foliar fertilization is to supply plants with the nutrients needed for good growth. There are many products on the market that can be used as foliar fertilizers, but are they really needed? Is there any advantage to foliar application instead of soil application? In this article we’ll review situations where foliar fertilizers may be beneficial and situations where their use is questionable at best.
When It’s Not Such a Great Idea
For all landscape and garden plants, the major pathway for nutrient uptake is by way of the roots. Leaves have a waxy cuticle, which actually restricts the entry of water, nutrients, and other substances into the plant. To a limited extent nutrients applied to leaves can be absorbed and used by the plant, but for the major nutrients (nitrogen, phosphorus, potassium) the quantity absorbed at any one time is small relative to plant needs. That means that foliar application of these three nutrients can only supply a very small fraction of the total needed by the plant, so foliar application should be considered only a supplement to regular soil application of these nutrients. If the plant already has plenty of nitrogen, phosphorus, potassium, foliar application will not have any beneficial effects. In fact, if concentrations of nutrients in the foliar spray are too high, then leaf damage can occur and in severe cases may kill the plant.
Here’s a calculation to show how hard it would be to get the required amounts of major nutrients into plants through foliar application:
For a vegetable garden, a typical recommendation for nitrogen is 0.15 pound per 100 square feet of garden area. A commonly available soluble fertilizer is 20-20-20 with a recommended rate of 1 tablespoon of fertilizer per gallon of water. It will take 0.75 pound of fertilizer to apply 0.15 pound of nitrogen to 100 square feet. One tablespoon of the fertilizer weighs about 0.35 ounce, so it will take about 34 tablespoons of fertilizer (dissolved in 34 gallons of water) to supply the right amount of nitrogen.
That amount of water will deliver about 0.6 inch of water to 100 square feet, which may not seem like much until you start thinking in terms of moisture films covering leaf surfaces. It will take only a very small fraction of 0.6 inch of water to completely cover the plant foliage, especially when plants are small (and that small stage is when plants really need the nutrients). Even if we allow for potentially greater efficiency of nutrient use with foliar vs. soil applied fertilizer, it would still be impractical if not impossible to provide all the foliar applications needed to deliver enough nitrogen in a timely manner.
A distinction needs to be made between foliar fertilization and the application of soluble nutrients in liquid form where the majority of the nutrients taken up by plants are absorbed by the roots from the soil. When liquid fertilizer is sprayed on foliage some nutrients are absorbed through the leaves and light, frequent applications would constitute true foliar fertilization. However, with heavier spraying there will be considerable runoff from the foliage and the liquid fertilizer will soak into the soil. In this case there would be some nutrient absorption through leaves, but the majority of the nutrients used by the plant would actually be taken up by roots. From the plant’s perspective, this is essentially the same process that occurs when dry fertilizer is added to the soil. Although it will be more expensive and time consuming than a dry fertilizer application, it is certainly feasible to meet the plant nitrogen need in the problem above by applying 0.6 inch of liquid fertilizer in a series of applications. Phosphorus and potassium, however, move very little in most soils from their point of application, so it’s better to work them into the soil before planting to make sure they’ll be within the plant’s root zone.
When It’s a Pretty Good Idea
An appropriate time to consider foliar fertilization is when a specific nutrient shortage is evident based on visual symptoms or soil analysis. If a deficiency exists, then foliar application would be one means of providing a quick but temporary fix to the problem. Certain soil conditions such as high pH, low pH, drought, excessive moisture, or cool temperatures may cause some nutrients to be unavailable for uptake by the roots. If any one of these conditions exists, the problem may be more effectively corrected with foliar applications than with soil applications.
If your azalea's foliage is chlorotic a foliar application of iron may help. Dave Hansen
A classic example of effectively using foliar fertilizers is for micronutrients such as iron. At high soil pH levels, iron is not available to plant roots even though high levels of iron may be present in the soil. Some plant species such as blueberries, azaleas, rhododendrons, and pin oaks are more sensitive than others to high pH. Under high pH conditions, iron chlorosis or interveinal yellowing occurs on young leaves. (See David Zlesak’s article in this issue, above). While lowering soil pH or selecting plants tolerant of high pH conditions are the preferred long term solutions, a way to alleviate the chlorosis temporarily is to apply inorganic salts such as iron sulfate or chelated forms of iron directly to the leaves. Chelates are chemical compounds that help iron stay in solution over a wide pH range. A general recommendation for iron sulfate is 0.8 ounces per gallon of water. For chelated forms, follow the directions for rates to apply on the label of the specific product selected. Make sure that the spray fully covers the leaves. Applications of iron are most effective shortly after leaf emergence and only on those leaves that have been sprayed. Iron will not move to leaves emerging after a spray, so new leaves will be chlorotic. Usually two or three applications are needed to ensure that all newly emerging leaves are covered. Foliar iron sprays will need to be reapplied yearly, unless steps are taken to change the underlying soil pH problem.
The cuticle on leaves of most plants will cause water to bead up and prevent good penetration. So, for all foliar applied products, it is important to include a wetting agent or surfactant to allow for full coverage of the leaf. One or two drops of detergent per gallon of water will help to wet the leaf surface. If rain occurs shortly after an application, most of the spray will be washed off the leaves and reapplication will be necessary.
Important points about foliar fertilization:
Mulch holds in valuable soil moisture and moderates soil temperature, so apply an appropriate mulch to any bare ground in gardens and landscaped areas. Use 2 to 4 inches of coarse, long-lasting mulches like wood chips or bark nuggets around trees and shrubs. Use faster-decomposing mulch like straw, shredded leaves, or cocoa bean hulls in areas where soil is turned frequently like vegetable gardens or annual flower beds.
Use soaker hoses in gardens to apply water directly to soil without wetting foliage. Cover soaker hoses with mulch. This helps extend their life by protecting the hoses from UV rays.
Be sure to water all trees and shrubs planted this year or in the past few years if rainfall has been insufficient in your area. These plants are still developing root systems and can be easily damaged or killed if allowed to dry out.
Small fruits like raspberries and blueberries need even soil moisture now as their fruit develops.
Be aware of any watering restrictions in your community. Save water by watering lawns in early morning when winds are light and temperatures are lower.
Raise mowing height to 3 or more inches and be sure mower blades are sharp. Grass blades can lose more water when the tops are shredded rather than cleanly cut.
Watch for squash vine borer adults (a clear winged moth). Females are already laying eggs on squash stems; larvae then bore into stems and can kill squash plants. Remove the tiny brown eggs if you see them.
Blossom-end rot often appears on early tomotoes that have suffered uneven soil moisture conditions, so water tomatoes regularly and mulch well to hold soil moisture and reduce soil splash which can spread fungal spores.
Deadhead perennial and annual flowers to improve appearance and encourage more bloom.
Look for good deals on annuals and perennials at garden centers now.
Protect yourself from mosquito bites by wearing long sleeves, long pants, and even a head net; or use an effective mosquito repellant spray. Don’t forget to protect yourself from the sun as well by shielding skin or using liberal amounts of sunscreen. You spent good money for that fancy garden hat, so use it.
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Happy gardening!Nancy Rose
Editor
Regional Extension Educator - Horticulture
Home « Gardening News « July 1, 2007