Garden Variety: Protect soil with organic matter

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Fall is a good time to amend soil in existing landscape and garden beds and prepare new beds for planting. The type of soil typically found in yards in the Lawrence area could definitely use improvement before planting to get plants off to a good start. Established beds also need attention from time to time.

Doing the work in fall gives the freshly worked ground a chance to settle over the winter (and be all ready when the planting bug comes in spring), and the mild temperatures but still-warm soil make the work quite pleasant.

Most yards in the Lawrence area have soil with at least some clay in it and a high soil pH. Clay makes soil heavy and sticky when it is wet, and it can hold water for days. That might sound OK for summer, but the holding of water against plant roots prevents oxygen movement and makes a favorable environment for root rot diseases.

The best way to improve poorly drained soils is to add compost and/or organic matter. Compost is decayed organic matter, made from leaves, grass clippings, food wastes and other plant materials. In a finished, ready-to-use state, it is dark brown to black and has a consistency similar to ground coffee.

Compost helps create space between soil particles, improving drainage and air movement. There is also a lot of microbial activity in compost (beneficial fungi, bacteria, and other microorganisms) that improves the overall health of the soil and makes existing nutrients more available to plants.

There is an old wives’ tale about adding sand to poorly drained soil to improve drainage. This is another idea that seems plausible on the surface, but getting the ratios right is nearly impossible. Instead, adding sand to heavy clay usually makes the situation worse, creating a consistency similar to concrete. Stick with compost to avoid complicating the problem.

In a new planting space, spread a few inches of compost over the entire surface of what will be the planting area. Till the compost into the soil, or use a shovel to dig several inches down and mix the compost into the existing soil.

In existing garden and landscape beds, add compost between plants and in open spaces and use a shovel or small manual cultivator to work the compost into the soil without a lot of disruption to plant roots. Perennial flowers can be dug and set aside for soil improvement, then replanted briefly after to make work easier. Avoid tilling or heavy cultivation under shrubs or directly under trees where there are a lot of plant roots.

Compost can also be used as mulch — placed on top of the soil surface as an insulating layer. Even on the surface it will improve microbial activity and soil health.

Once the compost has been mixed into the soil, add a layer of mulch over the surface of the entire planting area. The mulch insulates the soil surface, reducing temperature and moisture fluctuations. It also helps to prevent weed growth as it prevents light from reaching weed seeds within the soil.

Compost is available from most garden centers in bags or bulk, or from the city of Lawrence Compost Facility at 1420 E. 11th St. Bagged compost may be made from certain materials such as cotton burrs or manure. Bulk compost, including what is available from the city facility, is typically made from a mix of plant waste materials. Some gardeners have a favorite kind of compost. In research studies, there is little difference in kinds of compost used. Any compost is better than no compost.

The city Compost Facility is self load only for the rest of the season, but the compost is free. It is open from 9 a.m. to 3 p.m. Saturdays. It will close for the season in mid-December and resume Saturday availability in early spring.

— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation.


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