Released: March 10, 2004

Happy Plantings More Than Just a Matter of Fertilizing

COLUMBUS, Kan. – The long-advised and often-skipped soil test can tell home gardeners and lawn owners whether they’re working with very few soil nutrients or an out-of-whack pH. (See related story.)

“That’s important to know, but it’s certainly not everything. While planning for spring, gardeners also should be assessing other factors that can make a big difference in their success,” said Jacob Weber, Kansas State University Research and Extension horticulturist.

For example, soil tests provide no clue to whether plants are suffering because they’re simply in the wrong place. Lawn grasses can’t grow in heavy shade. Hostas burn up in a dry, sunny location. Japanese maples have trouble surviving almost anywhere in states such as Kansas.

“Using plants that are adapted to the environment where they’ll be growing is many times better than applying fertilizer, hoping to rescue or revive a badly sited plant,” Weber said.

Plants can struggle or die because of a location’s soil. In wooded river valleys and prairie sod, natural debris is constantly decomposing, recycling and increasing soil’s organic content, Weber said.

Home landscapes, on the other hand, generally need help. They often start out with a base of subsoil, pushed in place by a contractor driving heavy equipment. After that, every person, pet or piece of machinery that crosses the yard compacts its soil, limiting the air spaces (pores) between the soil’s smallest units.

“Soil oxygen is essential for roots to function well. Plants can be oxygen-deprived in soils that are compacted or otherwise don’t drain well, just as they can be moisture-deprived in soils that drain too well,” Weber said. “Ideally, soil with good structure should have one-half of its volume in pore space. When filled to capacity, it still should have half of that pore space filled with air and the other half with water.”

This kind of soil is crumbly, not clumpy, he said. It drains better than unimproved clay, but retains moisture better than unimproved sand. And, it’s easy to till.

“Unless you’re willing to move, you can’t do much to change your landscape’s soil texture – its combination of soil’s three building blocks: clay, silt and sand. But you can improve any soil’s air- and water-holding characteristics – its structure – by adding organic matter,” he said.

Most research suggests soils with a minimum of 3 to 5 percent organic matter provide the best structural environment for landscape plants.

Weber believes homemade, well “cooked” compost is always the best organic soil amendment.

“You can get into real trouble by adding some manures. They can be a good way to introduce the seeds of pernicious weeds,” the horticulturist said.

For example, in his part of southeast Kansas, he’s seen manures introduce Johnson grass, bindweed, and parasitic dodder – a Cuscuta species sometimes called strangleweed.

“Manures often aren’t a good idea in spring in any case,” Weber said. “Typically, they’re not fully decomposed, and their decomposition in the soil during the growing season can affect plant growth.”

Peat moss can be a good amendment, he said, “particularly out west, because it can lower soil pH. But if you use it in eastern Kansas, you’ll also want to get a soil test to ensure the pH doesn’t go too low.”

Weber said other ways to improve soil’s organic content include:

* Till in disease-free garden debris each fall, so it can “compost” underground over winter.

* Plant and incorporate cover crops and green manure crops.

* Use mulches such as wood chips or dried grass clippings, but don’t remove old organic mulch as it deteriorates around shrubs and perennials.

“These approaches will help with any soil compaction problems you have, too,” Weber said. “Then all you’ll have to worry about are such things as weather, planting at the correct time, mowing and pruning properly, and controlling pests ... in other words, all of the other things that no soil test can tell you need to be done.”

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K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by:
Kathleen Ward
kward@oznet.ksu.edu
K-State Research& Extension News