Last updated: March 21. 2014 10:14AM - 546 Views
By George McVey Contributing Columnist

George McVeyContributing Columnist
George McVeyContributing Columnist
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Last fall my lawn was thin and patchy. I hoped that it would fill in this spring but it is March and it hasn’t improved much. What do I do now?

If bluegrass lawns were damaged last fall and are patchy or thin, then a spring fertilization is recommended to encourage growth and increased density; bluegrass spreads via underground rhizomes. Apply 0.5-0.75 pounds of actual nitrogen per 1,000 square feet now, but avoid heavy spring fertilizer applications, which can lead to summer lawn disease problems.

If the lawn is comprised of tall fescue or perennial ryegrass and is thin or patchy, it must be overseeded, and March is the best time to accomplish this. If it is later than March, you may want to wait until fall to make lawn repairs rather than chance a late seeding.

In these lawns, it’s a good idea to apply a pre-emergent crabgrass control product, at least to deter this weed and a few others, from invading the patchy areas.

My spring flowering shrubs just don’t bloom like I think they should. I’m doing some pruning in late winter or early spring, just to shape them up — am I doing something wrong?

You may be pruning off flower buds, which accounts for your poor showing. If your plants bloom on “old” wood, then pruning in late fall or early spring removes some of the buds. A good rule of thumb is that for woody plants that normally bloom before about mid-June, prune after flowering (this will depend a bit on the season’s weather). This includes the following common shrubs; forsythia, honeysuckle, viburnums, serviceberry, mock orange, flowering quince, Itea, magnolias, lilac, weigela, firethorn, rhododendron and azaleas, a few of the spireas, and spicebush.

Small ornamental trees that bloom on old wood include redbud, fringetree, Kousa and Cornelian cherry dogwoods, smoketree, crabapples, flowering cherry and plum, and mountain ash. If in doubt about when to prune a plant, check a reference to find out whether the plant blooms on old or new wood.

I live in a new subdivision. The topsoil is horrible, making it difficult to maintain a healthy, green lawn. I use the recommended lawn care applications but they provide only a temporary fix. How can I improve the existing topsoil? Should I add another layer of new top soil over the existing grass?

Ideally, the soil should have been improved before the new lawn was seeded or sodded. You were probably left with subsoil after construction, which is high in clay content and low in nutrients and organic matter. At this point, you can work on improving the soil, but it will likely take several years.

Core aerating the lawn may help and it can be done annually. This practice improves the top couple of inches of soil and over time, will improve drainage, aeration, root growth, water and fertilizer infiltration, etc.

Another option for soil improvement is topdressing, but this should only be done in conjunction with core aerating. In this process, an eighth inch layer of topsoil is applied over the lawn. This light dressing of soil improves the environment at the soil surface and facilitates microbial activity. The applied soil should be similar in texture to the native soil to prevent drainage problems, while peat moss or other high organic materials should not be used, as these products will add to thatch buildup. Topdressing should not be added on top of an existing thatch layer, which would create a layering problem. Though topdressing is an option, it is not easy for most homeowners to do.

When should I apply spring fertilizers to my lawn?

Most homeowners place too much emphasis on spring and summer lawn fertilization. Some fertilizer is needed during spring and summer, however, over-application can cause diseases and other problems and result in “summer lawn nightmares.” If the lawn was fertilized late last fall, then you need to make only one application in late April or early May, using three-quarters of a pound of actual nitrogen per thousand square feet. If no late fall fertilizer was applied, you should make two applications this spring; one the first week in April, and the other about the last week in May, using three-quarters of a pound of actual nitrogen per thousand square feet each time.

I want to learn how to calibrate my lawn spreader so that I can use cheaper, off-brand fertilizer not specifically formulated for use with my brand name spreader. How can I do this?

Calibration means finding the spreader setting that delivers the desired quantity of fertilizer over a given area. There are two types of spreaders, drop and rotary. Rotary spreaders cover a wider area more rapidly than drop spreaders, but both will do a good job if properly calibrated. Both have a feed regulatory device that regulates the amount of fertilizer applied to the lawn. Higher numbers or letters typically increase the fertilizer output.

Using the actual nitrogen formula, you can figure out how much fertilizer needs to be applied per 1000 square feet of lawn. The challenge is to apply the correct quantity of fertilizer evenly. One option is to measure an area that’s 1,000 square feet (such as on a driveway), approximately 30 feet by 33.5 feet. As an example, you’ve determined that you should apply 5 pounds of fertilizer per 1,000 square feet; put 5 pounds of fertilizer in the spreader, select a setting, and run the spreader over the area. You may run out of fertilizer before you run out of driveway, or have fertilizer left. Adjust the spreader setting up or down, sweep up the fertilizer, and apply it again. It may take several trial runs to adjust the spreader correctly. You will have reached the correct setting when all of the fertilizer is applied over the 1,000 square foot area. Keep a record of the spreader setting for various brands or analyses of fertilizers, based on the percentage of nitrogen in the fertilizer.

I have taxus and junipers approaching 8 feet in height. Will they recover and grow back if cut them to about one foot from the ground, or will this excessive amount of leaf removal kill the shrubs?

The pruning you describe would be considered drastic for these evergreens, and may result in loss of the plant(s). Generally, when you wish to reduce the size of an overgrown shrub (rejuvenation pruning), pruning is done over a three year period to gradually return the plant to a useful size. These two species of plants have different characteristics that you should consider as you prune. Yews (Taxus) have dormant buds along older stems that will eventually break and grow new stems and foliage, and are more likely to recover from heavy pruning than junipers. Junipers can be cut back to green tissue, but are much less likely to come back from older wood that does not have any green foliage associated with it. Keep these things in mind as you prune. You could reduce the size of these shrubs by a third starting early next spring, and continue with rejuvenation pruning over the following couple of years to try to reduce the size of the shrubs.

Is April too early to apply mulch to shrub borders and flower beds? How much should be applied?

It is best to wait for the soil to warm and dry out before applying spring mulch to landscape trees and shrubs. If applied to cool soil, it keeps the soil cool and slows root growth. Late May or early June is the usual time for application in central Ohio; apply a little earlier in southern Ohio and a little later in northern Ohio.

Don’t overdo mulch; a two inch layer is sufficient over heavy clay soils to conserve moisture, suppress weeds, and moderate soil temperature. Greater depths could cause problems for plants by keeping soil too wet or reducing oxygen availability to root systems. Avoid placing mulch against the trunks and stems of trees and shrubs, and keep it a few inches away from crowns and stems of non-woody plants.

George McVey, Ph.D. is a Master Gardener volunteer.

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