Using Liquid vs. Dry Fertilizer and Fertilizer-Herbicide Combinations
Using Liquid vs. Dry Fertilizer
It is quite common to apply lawn fertilizer dissolved in a liquid rather than as a granular material. It makes little difference to the plants whether the nutrients are applied in liquid or dry form. Plants are able to use nutrients absorbed through the foliage as well as the roots although the majority of nutrient uptake occurs in the roots.
Lawn fertilizers are commonly mixed with herbicides to reduce the labor involved in lawn maintenance. Care should be used in applying these products. Fertilizer applications should be a regular lawn maintenance practice, but herbicides should be used only when specific weed problems occur. For effective weed control, herbicides are used at specific times during the year, sometimes differing for various weeds. The time of year for herbicide effectiveness may not be the optimum time for fertilizer application.
An additional problem with some combination products is that fertilizers should be watered-in following application for maximum effectiveness and low burn potential, while many herbicides need to remain on the plant leaves for effective weed control. Consequently, by using fertilizer-herbicide combination products you often compromise the effectiveness of one or both products from a timing or application standpoint, or both. Certainly fertilizer-herbicide combinations should never be used when the herbicide would be ineffective or unnecessary. Always check the specific product label for any post application requirements (e.g., whether it should be watered-in or not).
Another issue with fertilizer/weed killer combination products is that they often apply significantly more herbicide to the area than is needed to kill the target weeds. Where there are only scattered weeds throughout the yard, it is just as easy to spot treat those individual weeds or small areas of weeds rather than applying a weed 'n ' feed product over the entire lawn. It's also important to remember that those combination products specifically formulated for broadleaf weed control require contact with the foliage of the weed. Hence, weeds must be visible and actively growing at the time of application to be most effective. Applying this type of product over the entire lawn hoping to prevent broadleaf weeds from getting started is ineffective.
A notable exception to the above would be the fertilizer / crabgrass killer combinations as they contain a preemergence weed killer specifically targeting the tiny seedlings as they just emerge from the seed, but before they are visible above ground. In lawns, these products target the annual grassy weeds, such as crabgrass and yellow foxtail. If a spring application of fertilizer is being put down around the early part of May, at least in most years, then fertilizer products that contain a crabgrass killer could be an appropriate choice. Again, as with most weeds, the severity of infestation will not likely be uniform over an entire yard. Thus, a crabgrass-preventer may only need to be applied along those areas where the bluegrasses and other lawn grasses aren't as competitive. These include areas along curbs, sidewalks, narrow boulevards, driveways, etc.