FO-06594     1997

To Order

Roses for the North

Cultivation Tips

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Site Selection

A site that provides full sunlight, good air circulation, and a well-drained soil high in organic matter is ideal for rose growing. Roses receiving fewer than six hours of sun daily will be leggy, less floriferous, and more disease-prone. The number of roses that grow and perform well in partial shade is small. If roses are crowded by neighboring plants or buildings, air movement is restricted and disease incidence increases.

Water movement through the soil should be slow enough to allow water and nutrients to be absorbed by roots. But excess water must be able to drain away quickly, because rose growth and performance deteriorate rapidly if roots are waterlogged. If an 18-inch hole filled with water drains in six to eight hours, drainage is satisfactory. Soil that drains more quickly is sandy and can be improved by the addition of organic matter such as composted plant materials, peat moss, or composted manure. Adding organic matter will improve the texture and drainage of compacted or clay soils that drain too slowly.

When soil drainage problems cannot be corrected, raised beds can also be used for growing roses. Construction materials for the beds must be carefully selected because creosote or copper-treated timbers are toxic to roses.

Checking soil pH and nutrition prior to planting is important. A soil pH of 6.0 - 7.0 optimizes nutrient uptake in roses. Nitrogen moves easily through the soil and can be applied before or after planting. Phosphorous and potassium do not move easily or far in soil, so it is more effective to incorporate them prior to planting. County extension agents can refer gardeners to laboratories that can analyze soil samples and recommend amendments to optimize fertility and pH for a rose garden.

Garden size depends on the number of roses being planted, their mature sizes, and on spacing between plants. Remember that good air flow around roses results in healthier plants, and space your plants accordingly. Because of rose thorns, it is also important to leave enough space between plants to ensure that maintenance can be done as painlessly as possible.

Purchasing Plants

Local nurseries usually sell roses as container-grown plants that are actively growing and sometimes blooming, so gardeners can see what plants looks like before purchasing them. Container-grown plants can be planted any time through the growing season. Because of the additional care and handling involved in potting and forcing a bareroot plant into growth at the nursery, container-grown roses are more expensive than bareroot roses.

Mail order companies provide a more extensive choice of roses. Most are shipped dormant, with bare roots wrapped in a moisture-retaining material. The time of year that mail order sources ship roses depends on where you live. In Minnesota, expect shipment in early to mid-May.

The Combined Rose List 19 and the Andersen Horticultural Library’s Source List of Plants and Seeds 20 are international and national listings, respectively, of retail sources for particular rose cultivars.

Most roses are propagated by budding, which is the placement of a bud from one cultivar onto a rootstock of another. Rootstocks are usually thornless selections of the species R. multiflora or R. canina. The bud union, the site where the cultivar and rootstock are joined, is a distinctively swollen area on the shank. All basal canes of the cultivar emerge from the bud union. The rootstock used in budding often furnishes the plant with extreme vigor. For the gardener, this means that a plant may have a larger mature size than it would if it were on its own roots. For the rose propagator, it means that sizable plants can be produced quickly, consistently, and economically.

The rootstock of a budded rose will often send up suckers with flowers and leaves completely different from the variety budded onto it. Removal of these suckers can be a constant chore for gardeners.

Incompatability between a rootstock and the budded variety can occur. When this occurs, the vigor and quality of the budded cultivar declines over time, until finally the cultivar dies, leaving only the rootstock to send up new canes.

In northern climates, low winter temperatures can injure the bud union and cultivar growing above the union. Planting the rose with the bud union below ground for insulation is the best way to ensure bud union survival, so that new canes produced in the spring are from the cultivar rather than the rootstock.

Because of consumer demand, especially among northern gardeners, own-root roses produced by softwood propagation are becoming more available. These roses are produced by inducing roots to form on stem cuttings. With own-root roses, the chore of removing rootstock suckers disappears. Plants growing on their own roots are also often long-lived in comparison to budded plants. Since the root system is genetically identical to the canes, the gardener is assured that new basal canes produced each year are true to the cultivar.

Newly purchased budded roses vary in size. All plants should have a well developed root system, but the number, length, and diameter of canes will vary with grade (1, 11/2 , or 2). Grade 1 roses are the highest quality and the most expensive. They have three or more canes growing from the bud union for most rose classes. Grade 2 roses have the fewest, shortest, or thinest canes.

A cultivar budded and grown in a warmer climate is often larger than the same cultivar budded and grown in a cooler climate. The plants are genetically identical, but there are size differences due to the effect of climate on growth rate. Bigger is also not always better, since larger plants are more susceptible to transplant shock.

Newly purchased softwood-propagated roses also vary in size, ranging from small, 6-inch, potted plants that need additional care and container growth before being planted, to bareroot, 3-foot plants.

After receiving a rose, whether potted or bareroot, it is essential to keep the roots moist. Potted roses that cannot be planted immediately should be placed in a warm spot out of the wind, and soil moisture should be checked daily. If receiving a dormant bareroot rose, open the package as soon as possible. If you can plant immediately, immerse the rose in a bucket of water for at least a few hours before planting to rehydrate the plant. If you cannot plant immediately, check to see that the roots and the moisture-retaining material around them are still moist, wrap the rose back up in its plastic covering, store it in a dark, cool spot, and check the plant’s moisture level daily. If the ground is not frozen, bareroot roses that will not be planted within two weeks of shipment should be temporarily heeled in. Dig a trench or hole in the ground, lay the rose in it, and cover the roots and canes with moist soil.

Planting

Potted roses can be planted at any time during the growing season, but the earlier the plant is put into the ground, the more time it has to establish before the onset of winter. Bareroot plants should be planted in early spring while they are still dormant. Unless very heavy mulch is applied, fall planting of roses is not recommended in northern areas because soil temperatures drop too quickly to allow root establishment.

Planting on a calm, cloudy day avoids desiccation of roots and canes. Begin by digging a hole twice as wide as the root ball diameter. If organic matter needs to be incorporated, mix compost, composted manure, or peat moss with the soil from the hole. Incorporating bonemeal into the soil at this time provides a long-term source of phosphorous and promotes rooting.

Minimize root disturbance when planting a potted rose. If possible, cut the bottom of the container out, place the pot in the planting hole, slit the side of the pot, and remove it. If the roots are a dense mass circling the perimeter of the root ball, shallow cuts should be made in several places down the side of the root ball. This encourages new root growth out into the surrounding soil.

On bareroot roses, any broken canes or roots should be trimmed away. If roots are excessively long, shorten them rather than twisting them around the bottom of the planting hole. Prune the canes back to a height of 6 to 8 inches. This encourages basal bud breaks and creates a stronger, bushier plant.

If the plant was propagated by budding, place the plant in the hole with the bud union 2 to 4 inches below ground level. This insulates and protects the bud union. Plant an own-root rose at the same depth at which it was previously growing.

Put half of the soil back into the hole around the roots, tamp it lightly to eliminate air pockets, and add the remainder of the soil. Construct a rim of soil around the planting hole to create a shallow well, and water the plant thoroughly by filling the well.

Mound 6 to 8 inches of soil up around newly planted dormant rose bushes. Keep this mound moist so that the canes and buds within remain moist until the buds break, typically within about 14 days. When buds start to expand, gently wash the mound of soil away, preferably on a cloudy day.

Hardiness Zones: The winter hardiness evaluation reported in this bulletin was conducted in Zone 4a, where average annual minimum temperatures ranges from -25 ° to -30°F (-32&$176; to -34°).

Water, Mulch, and Fertilizer

The common rule for rose irrigation is 1 inch of water per week during the growing season. This is especially important during the first growing season of a newly planted rose.

The amount of water needed by established roses depends on the soil it is planted in. Roses in sandy soils will need more water than those in heavier soils. Excessively hot temperatures for extended periods call for more frequent watering. Mulched beds retain soil moisture longer than unmulched beds.

A slow, soaking application of water which penetrates 15 to 18 inches into the ground is best. Wetting the foliage of roses during irrigation should be avoided to discourage disease development.

Mulches help retain soil moisture, moderate soil tempertures, decrease erosion, and discourage weeds. Organic mulches such as wood chips, straw, and grass clippings will improve soil quality as they break down. However, large amounts of nitrogen can be bound up as an organic mulch decomposes, often at the expense of the roses, so additional applications of nitrogen may be needed. Organic mulches that decompose need to be reapplied regularly.

Fertilization programs should vary depending on rose type. One application of a balanced fertilizer in early spring is adequate for Species Roses. All other roses will benefit from a second application at the end of the spring bloom period. A third application in late July helps repeat-flowering and continually blooming roses. Fertilization after August 1 is not recommended, because this encourages new growth and delays cold hardening.

Deadheading

Deadheading is the removal of spent flowers from a rose bush so that hips, the rose fruit, do not form. This maximizes rebloom on repeat-flowering roses by diverting the energy normally used for hip development into new flowers and cane growth. If a rose is female-sterile, deadheading occurs naturally as spent flowers drop off the plant.

The only reasons for deadheading a one-time-blooming rose are to give the plant a cleaner appearance or to maximize vegetative growth. Not deadheading these roses or any rose whose rebloom is less than showy allows gardeners to take advantage of the ornamental value of fall hip display.

Methods for deadheading should vary between types of roses. For instance, the usual method of deadheading Hybrid Teas and Floribundas is to remove a spent flower and the cane beneath it back to the first outward-facing leaf with five leaflets. Deadheading back to a leaf with fewer leaflets often results in non-flowering new growth, called “blind wood.”

The location of new shoot and new flower formation is more variable among hardy repeat-flowering roses. New flowering wood can be produced from a bud at the bract beneath a flower or from buds at any leaf axis. On these roses, it is better to deadhead back to the bract beneath the flower, and observe whether new flowering wood grows from this point. If flowers are not produced, prune back to the first leaf and start the observation process again. Continue deadheading back to the highest leaf on a cane until you know the pattern or growth and bloom for a cultivar.

Do not deadhead after August 1. This allows hips to form, which signals the plant to slow its growth and go dormant in preparation for winter.

Pruning and Winter Protection

There are several reasons to prune a Shrub Rose besides deadheading to maximize rebloom. Pruning a newly planted rose to a height of 6 to 8 inches minimizes transplant shock, making the establishment process easier for the plant. It also encourages bud break at the base of the plant, producing fewer and stronger canes and a denser form.

In northern climates, winter injury to canes can be severe. Pruning to remove this injured wood is done in the spring. As roses age, it is often necessary to remove old canes that have become less vigorous and less floriferous. Removing these canes opens the center of the plant, encourages new cane formation, and improves air circulation. One-third of the canes can be removed annually without hurting the plant.

Removing weak, spindly growth from a rose allows it to divert its energy to stronger, more vigorous canes. This improves the health of the whole plant. Pruning is also done to alter and improve plant habit or size.

Providing winter protection for a newly planted rose will improve its chance of surviving the first winter, before it has completely established. After roses are established, a gardener’s choice of the level of winter protection to be provided should be guided by two factors: the hardiness of the cultivar and the level of cane injury acceptable to the gardener. Local nursery operators and rosarians may be able to provide information on a rose’s hardiness level during a typical winter in your area. Because descriptive text on a new cultivar may also list the rose as hardy to a particular temperature or hardiness zone, North American plant hardiness zone maps, such as the one on page 76, can also be a valuable aid in selecting appropriate cultivars. Individual gardeners then have to decide how much cane injury is tolerable, and protect roses accordingly.

Snowcover, when present, is a natural insulator of rose canes. The tipping and covering, soil mounding, wood chips, and leaves enclosed with chicken wire are ways to provide winter protection.

Pest Control

Recommendations for controlling diseases and insects with chemical pesticides change constantly as old products are removed from the market and new ones become available.

The best way to keep abreast of current pest control recommendations is to obtain the most current university extension publications 21 or to contact local county extension agents. Consulting Rosarians in rose societies can also often recommend control programs.

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