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The Garden Plot for March 28, 2008
3:55 PM - 4:00 PM
[Program Website]
Today's Highlight: “Organic Lawn Care”
We get a lot of questions at the Extension office about organic lawn care. Is it possible? Absolutely. But, sometimes the organic approach is a bit more costly. Organic lawn care starts with good soil. Good soil for lawns is high in nitrogen, phosphorus, and organic matter with a pH of 6.5 to 7.0. Composts addition is a good way to increase soil organic matter and add nutrients.
In Missoula County, we have experimented with compost additions to improve soil health and alleviate soil compaction. Compost applied to lawns at ˝ - 3/4 inches in the fall and/or in the spring is a great fertilizer option. Grass clippings left on the lawn with a mulching lawn mower also provide a balanced lawn fertilizer. However, if you like a dark green lawn, you may need to add an extra nitrogen source occasionally, along with the compost and grass clippings. We added pelletized chicken manure to our study plots and saw a rapid greening up response. Compost applications may also suppress disease. California studies have shown that monthly applications of as little as 10 pounds of compost per 1000 square feet can effectively suppress fungal diseases. Composts that include manure or biosolids appear to be the most disease-suppressive types of compost and the best suppliers of nitrogen.
Aeration also improves soil quality and helps grass plants develop and maintain strong roots. Aeration helps to alleviate soil compaction. Ever notice that dandelions get started in the parts of the lawn where people and pets walk frequently? Compacted soil makes dandelions more competitive than grass plants. You can aerate your lawn twice per year (spring and fall), but once a year is enough if you do not have heavy foot traffic. The only time NOT to aerate is when dandelions are in full bloom.
The best defense against lawn weeds is to grow the most vigorous turf possible. Weeds have a tough time invading a thick turf with well-developed roots. The grass variety you choose affects your lawn’s competitive ability. Some grass varieties do better in shade, some can handle less irrigation. If you have a shady lawn and weeds that like to grow in shade, a sun-loving grass variety is a bad choice; it will succumb to shade-adapted weeds.
Irrigation amount and frequency can also encourage weed problems. Providing inadequate irrigation to a water-dependent grass variety such as Kentucky Bluegrass allows drought tolerant weeds such as Dandelion to move in. On the other hand, frequent short-duration irrigation encourages shallow grass root growth and allows deep rooted weeds (like Canada thistle) to establish. To encourage deeper lawn root growth, water less frequently but for longer periods. This approach will also grow stronger grass leaves to shade out weed seeds (like the ubiquitous Dandelion seed).
Mowing can encourage or discourage both weeds and turf grass. In our Montana studies, lawns that were allowed to grow to a height of at least 3” during the hot, dry, stressful months of July and August were healthier and better able to resist weeds. Organically maintained lawns should be kept to a height of at least 2 inches or higher. Grass plants need enough leaf surface to act as energy-harvesting solar collectors. Grass plants use the harvested energy from the sun to grow strong roots. If you continually mow too short, especially when lawns are stressed by hot, dry conditions, you can actually decrease grass root size and, over time, diminish soil organic matter.
In summary, organic lawn care is not difficult: Add annual or bi-annual high nitrogen compost applications, aerate, and irrigate to grow strong roots and thick turf so that there is no room for weeds to sneak in.
Helen Atthowe's new short program of gardening tips
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