Lawn

Aeration of zoysiagrass

I have a heavy clay lawn with much foot traffic from the kids. Will liquid gypsum work much faster than applying pellet gypsum? Is it safe for the lawn, and are there any negitive risks involving gypsum applications?

Gypsum helps in improving the soil structure, permeability and drainage of the soil. It is mainly useful in improving salt affected soils. Missouri soils in general contain large quantities of clay and small amounts of soil organic matter. In established lawns it is difficult to correct problems caused by heavy, clay soils. Compacted soils can be improved by aerating the lawn in the spring and fall.

Gypsum provides the calcium that helps in aggregate formation and thereby improves the structure. Missouri soils in general have sufficient calcium. A soil test will tell whether the calcium levels are low or not and if low will tell how much gypsum could be applied. In general on established lawns about 40 to 50 pounds of gypsum per 1000 square feet, applied two times pet year would be sufficient. The gypsum can be surface applied using a spreader. I do not have any experience on the use of liquid gypsum. However, I would expect it be quick reacting with the soil. You can follow the instructions on the label for application rates. There won't be any negative effects in applying gypsum.

Manjula V. Nathan
Director
Soil Testing and Plant Diagnostic Services

Aeration of zoysiagrass

When is the best time to aerate a zoysia lawn?

Core aeration is one of the most important cultural practices that can be provided to lawns. The most active growth period of the grass will determine the time core aeration should be done.

Cool season grasses, like tall fescue or Kentucky bluegrass, should be aerated in March, April or September. However, a zoysia lawn should be aerated anytime from May through July.

I suggest homeowners aerate their lawns at least once a year unless it is newly seeded or the soil is a sandy texture.

The greatest benefits from aeration will be seen in lawns with clay soils. Heavy soils are more prone to drying out quickly in the summer, allow less oxygen to the roots, and have poor water movement through the soil.

The presence of heavy equipment and foot traffic on the lawn will also contribute to lawn compaction.

Core aerator machines are equipped with hollow tines that punch and pull out a narrow core of soil, and deposit it on top of the grass. They can be found at most equipment rental stores.

Best results are achieved when soil moisture allows the tines to penetrate easily into the upper three to four inches of the soil. The proper time to core aerate is after a good rain or thorough irrigation.

Spacing of the holes is important. I suggest at least three passes over your lawn with the aerator in different directions to achieve good results.

Gaylord Moore
Horticulture Specialist

Spreading lime

I have a drop spreader and need to spread some lime on my clay soil yard. The bag only says to spread 40 to 80 pounds per 1,000 square feet. What setting should I use for the spreader?

Your question is difficult to answer because the setting for your spreader depends on the particle size of the material being spread. Since this information is not known, WQ551, Calibrating Home Garden Equipment should help answer your question about how to determine the correct setting.

Lime is used to raise the pH for soils that are acidic (have a low pH). You should know that even though you may have clay soil, it does not necessarily mean that it is acidic. In fact, I have observed the clay soils in St. Charles County often have a pH that is not acidic -- thus they do not need lime. The only way to accurately determine the need for lime is by doing a soil test. County extension centers do soil testing through our office for $10. If you have never had your soil tested, I would recommend that you do so.

Scott Killpack
Agronomy and Natural Resources
County Program Director

Breaking down soil's clay

Will adding gypsum to my lawn help break down my yard's dreaded Missouri clay?

I am skeptical about using gypsum to loosen clay in Missouri. Use of gypsum is well established where long-term irrigation with high-sodium well water has resulted in a high level of sodium in the soil (sodic soils). Sodium tends to disperse clay particles, and this has a negative impact on the physical structure of the soil, which tends to get compacted and hard. Calcium helps clay particles to stick together and promotes good structure. So, in this specific case, applying gypsum (calcium sulfate), then irrigating like crazy helps wash the sodium down through the soil and replaces the sodium with calcium. This improves the physical properties of the soil.

If you look at a soil test for most Missouri soils, it will already have a high calcium content while the content of other major elements is much lower. In my opinion, there's so much calcium in the soil already that the benefits of calcium to help promote structure are already there. I seriouly doubt that adding more calcium will improve the situation. I would recommend a soil test just to be sure what level of calcium you have. Soil samples can be submitted through your local extension office.

Brad S. Fresenburg
Extension Research Associate
University of Missouri Turfgrass Research Center

Dethatching zoysia

I use a rake attachment on my mower and set it as low as it will go to dethatch my zoysia. Is this the right way to do it? It creates a fine dust difficult to clean from the lawn.

The rake you have on your mower is OK, but a dethatcher from a rental store would do a better job of pulling all thatch. If you do this in June when zoysia is actively growing, recovery should be quick. Fertilize immediately after dethatching.

Brad S. Fresenburg
Extension Research Associate
University of Missouri Turfgrass Research Center