Adding Compost to the Garden

Use caution when adding organic material to garden   

Bill Sevier: Ask a Master Gardener

Saturday, March 26, 2016

Q: Should I till compost into my garden soil to add fertilizer? What should I use? L. C., Sand Springs

A: It is almost impossible to go wrong adding organic material to any type of garden, although there are some warnings about what to use.

Organic materials contribute to the “soil tilth.” This refers to the general suitability of soil to support root growth. Tilth relates to the soil structure and presence of beneficial microorganisms, as well as the organic content. Soil needs to be loose enough to allow water and air to freely move through but also be able to hold on to enough water and nutrients for the roots to absorb them.

Sandy loam is the ideal mix of material, but often we have to deal with soils either high in sand or clay. Highly sandy soil allows water and nutrients to flow through too fast, while heavy clay slowly absorbs water and nutrients but binds them tightly when it does. Roots also have a difficult time penetrating heavy clay due to its tight structure.

Any organic material should be fully composted before added to soil. If not, the composting process will continue in the soil. When organic material decays, it uses the nutrient nitrogen (part of fertilizer) and may compete with your plants for nutrients. A work-around for this is to till in the incompletely composted material in the fall, to allow it to decay before the following spring.

Another warning about the use of organics involves the use of composted animal manures and biosolids (organic material recycled from sewage). These materials are high in salt before composting. Exposure to water percolation will eliminate it; if not, the salt can “burn” your plants. If fully composted, this is of no concern.

Composted organics are beneficial for soil tilth, and they do add essential plant nutrients. However, in manures from plant-eating animals — cows, horses, sheep and even exotics, such as elephants — the nutrient content is much smaller than most people imagine. Not only that, but the nutrients are released slowly, and it may be 1-3 years before the bulk of them are released and available to plants.

The importance of this is that plants such as fast-growing vegetables, which benefit from the addition of organics, often need more nutrients than organics are able to supply. In this situation, commercial fertilizers may be needed as well. For those wishing only to grow organically, there are some organics higher in nutrient content, such as blood, fish and cottonseed meals, milorganite, bat guano and some others. The problem with most of these is that they may not be readily available.

The bottom line is that any type of soil will benefit from most any type of well-composted organics. In vegetable and annual ornamental gardens, tilling in 2-3 inches of organics to a depth of 6-8 inches every year will optimize your plants’ growth.

For more information or to ask a question about gardening, contact the Master Gardeners at 918-746-3701 from 9 a.m.-4 p.m.

Garden tips

§  All cool-season vegetables, strawberries, asparagus and other small fruit may be planted this month.

§  Established broadleaf weeds can easily be controlled in lawns at this time with postemergent broadleaf herbicides. These herbicides are most effective in spring and fall when weeds are growing.

§  Cut down dead pine trees as soon as possible. Most of these trees died of pine wilt disease due to a nematode infection. The infection is spread by the pine sawyer beetle and dead pines are a source of infection carried by these beetles.