Use and Misuse of Gypsum and Lime

Never use gypsum, lime without prior research

Brian Jervis: Master Gardener

Saturday, November 26, 2016 12:00 am

Q: When is it best to apply gypsum and lime to my lawn? D. A. Tulsa

A: You should never use either one without specifically documenting a reason. Gypsum has been used in the past to improve the drainage of clay soils, and lime is used to treat overly acidic soils.

Gypsum is calcium sulfate and was once thought to be able to loosen heavy clay soils. Science-based studies have shown this not to be true.

Clay particles are so small and flat they pack down and present a barrier to water, nutrients and plant roots. Tactics to loosen these soils have been researched thoroughly and gypsum, along with other materials, has been shown not to be useful. The OSU handbook, E-1003, “Oklahoma Homeowner’s Handbook for Soil and Nutrient Management,” explains the origin of the gypsum myth.

Gypsum is appropriate to treat soils with calcium or sulphur deficiency, but this is not likely in our area. Gypsum is also useful to treat “sodic” soils, or soils that have been exposed to excessive amounts of sodium containing salts. These soils need to have the salts removed to be plant friendly. The calcium in gypsum will displace and correct the salt excess.

The ideal approach in dealing with heavy clay soils is to use raised beds. If raised beds are not an option, regularly tilling large amounts of organic material will improve the tilth of clay soils as it does with all other soil types.

The use of lime is useful but should always be based on the pH (measurement of the level of acidity) result of a soil test.

Lime, which is calcium carbonate, will raise the pH in soils, making it less acidic. The pH of soil is a result of several factors, one of which is the amount of rainfall. Rain filtering through soils tends to remove calcium and add hydrogen. Hydrogen in soil increases acidity; calcium reduces it. The more rainfall, the more likely the soil will be acidic.

Often people who are from states east of us will assume liming is needed regularly, as it was often needed there, but that is not the case in most of Oklahoma.

Average yearly rainfall in Oklahoma drops steadily from our eastern border to the panhandle. Because of this, on average, there is less soil acidity from east to west.

Most plants perform best in neutral to slightly acidic soil; this includes most turf grasses. According to the USDA, the optimum pH for fescue and Bermuda is acidic, in the range of 5.5 to 7.0. Our average pH in the Tulsa area, based on more than 1,000 soil test results performed by OSU is 6.8, which is favorable to turfgrass and other plants. So, on average, no lime is needed and if used might be harmful to your grass. A soil test will inform you of a need for lime.

Garden tips

§  Fertilize cool-season grasses like fescue with 1 pound nitrogen per 1000 square feet. This should be the last fertilization for fescue until next spring. Do not fertilize Bermuda or Zoysia until green-up next April.

§  Spring-flowering bulbs like hyacinth, narcissus and tulip, which are sold for “forcing,” can be potted indoors for a colorful winter display.

§  Tulips can still be planted outdoors through this month.

Options for Leaf Use in FAll

Fallen leaves can be asset to gardens

Bill Sevier: Ask a Master Gardener

Saturday, November 19, 2016

Q: What is the best way to dispose of leaves in fall? I would rather not put them in the trash. Andy B., Tulsa

A: There are much better options for leaf use than placing them on the curbside for trash pickup. There are several ways fall leaves may be an asset for your garden. They may be used for mulch, tilled into garden soil for organic enrichment, composted or simply mowed into the lawn. All of these options ultimately give you free fertilizer, mulch and compost.

Most of these options involve the use of a lawn mower, preferably a “mulching” mower. This reduces the size of a leaf pile about 10-fold and helps accelerate the ultimate decay and release of nutrients.

University-based studies have shown that mowing up to 6 inches of leaves into the lawn is not only safe, but also beneficial for all types of turfgrass if done properly. The lawn should be mowed tall (2-3 inches), and the leaves should be completely shredded so they fall below the top of the grass. There, they decompose rapidly, add nutrients and do not contribute to thatch or disease.

Leaves also make great mulch for your garden, especially if shredded with a mulching mower. Shredded leaves added to your garden beds in the fall should completely decompose into usable organics and nutrients by the following fall, ready for another application. If they are not shredded and simply piled up in the bed, they may become soggy, decompose more slowly and prevent adequate passage of water and air.

The myth that some leaves, especially oak leaves, may add acidity to your soil, is simply not true. Good studies have shown that most all of the standard mulches have no effect on soil pH, but they all do add nutrients.

These same shredded leaves also may be directly tilled into the soils of your garden beds this fall. If added to the soil in fall, they will compost, and the bed should be ready by spring for planting of either vegetables or ornamentals. If the leaves are tilled into the garden in spring, rather than fall, they may compete with your plants for nutrients until decomposed.

It is highly desirable to have a compost pile for garden wastes. Leaves and most other yard wastes may be changed into a valuable garden addition. To get started, OSU has a fact sheet, “Backyard Composting in Oklahoma,” which offers complete information on compost bins and what may and may not be composted. This is available on the OSU Tulsa Master Gardeners website, tulsamastergardeners.org.

Don’t forget that Tulsa has an excellent free green-waste site, 2100 N. 145th E. Ave., for yard wastes, including large tree parts. The site is open daily, except city holidays, and is free to Tulsans with a proof of residence. There, all your yard wastes, including leaves, will be shredded into mulch for all. This service is free, and you may also get free mulch, as much as you want.

Garden tips

• Remove all debris from the vegetable and flower garden to prevent overwintering of various garden pests.

• Start new garden bed preparations now. Till plenty of organic material into the soil in preparation for spring planting.

• Cover water gardens with bird netting to catch dropping leaves. Take tropical water garden plants indoors and stop feeding fish when water temperatures near 50 degrees.

Fall Clean-up is Important to Prepare for Spring

Fall clean-up will Benefit spring planting

Brian Jervis: Master Gardener

Saturday, November 5, 2016

Q: Should I cut the tops off of my lilies in fall or wait until spring? T.C., Owasso

A: Both times are acceptable, and what you do depends basically on the appearance you are striving for in your landscape. This brings up the topic of fall activities in the garden that may help increase the performance of ornamentals and vegetables the following spring.

The option of removing leaves and stems of perennials applies to many plants other than lilies. Generally, it is best to leave perennial leaves attached to the plant as long as any parts are green. When green is present, the plant is still making energy and storing it in roots or bulbs.

One of the exceptions to removal of all plant parts from perennial ornamentals is when one wishes to save seeds for birds. Plants like purple coneflower have heads loaded with seeds that the birds can eat over the winter.

Lilies have long leaves that if left in place after browning and falling over, serve as a type of mulch to conserve water and moderate ground temperature. Also, if left in place, they may be pulled by hand or raked, as they are easily detached in spring. If for appearance sake you wish to remove the leaves in fall, it is best to mulch the lilies for the winter after the first frost.

Recommendations for fall cleanup in the vegetable garden is the same for ornamentals.

The tops of perennials such as asparagus should be handled like lilies. Annuals such as tomatoes and members of the squash family will develop disease and insect problems in the course of the growing season.

Many of these plants will harbor disease-causing microbes and also various overwintering insects and eggs in the material left behind after harvest. If left in place, the disease and insect numbers will build up and increase in severity from year to year.

So for vegetable gardens, it is best to remove all of the debris from last summer’s crop. After removing the debris, it helps to till the garden to expose any undesirable microbes or insects to the effects of winter.

Also, the fall is a good time to till organic material into your garden. Any composted organic supplements will benefit the soil when added in spring or fall. Even though some of the organics, such as leaves, might not be fully composted when added in fall, they should decompose over winter and be good to go in the spring. Some gardeners also will plant winter-hardy cover crops such as Austrian winter peas and winter rye. These cover crops protect the garden soil, and when tilled into the spring garden, they add desirable nutrients and organics to the garden.

Other suggestions for your garden beds is to obtain a soil test. This will give you sound advice about what fertilizers and amendments to add to the garden in fall and in springtime.

Garden tips

§  Leftover garden seeds can be stored in an airtight container in the refrigerator or freezer until next planting season. Discard seeds more than 3 years old.

§  The garden centers still have large selections of spring-blooming bulbs for sale. If you intend to plant bulbs, buy them and plant soon. Tulips can still be successfully planted through November.

§  Be sure to keep leaves off newly seeded fescue. The sprouts will die without sun and air exposure.