Organic fertilizers and good horticultural practices are only two aspects of organic lawn maintenance. You may still have weed and insect issues to contend with.
Weeds
Organic week control in a lawn is a problem because there are no selective organic controls, such as a broadleaf weed killer that only kills broadleaf weeds. Organic herbicides are made from horticultural strength vinegar (usually a 20% concentration compared to a 3 % concentration for what we use in the kitchen) or horticultural oil extracts such as oil of thyme, mint or rosemary. They are non-selective (think Roundup) and will kill any vegetation they come in contact with. They work best in a flower or perennial bed where the ornamentals can be protected from any over spray. In a lawn, the most organic method is to pull them by hand.
Preventing weeds from germinating in the first place by using a pre emergent herbicide, is one way to limit weed growth and here there is an organic alternative. The ability of corn gluten to inhibit root growth was discovered at Iowa State University in the early 1990s. It has been growing in popularity ever since. It is a bit tricky to use and get good results. Timing is critical. Several companies package corn gluten, including Bradfield Organics. Make sure you are using 100% corn gluten. Apply it at the rate of 20 pounds per 1000 square feet about 4-6 weeks before the weeds are expected to germinate. This is the tricky part. Most seeds germinate when the soil temperature is between 68̊–86̊ degrees fahrenheit but trying to estimate exactly when that will happen when the weather is so variable here in Northern Illinois is hard. Also, if it is too rainy during the germination period the corn gluten gets diluted and is not effective. On top of that, corn gluten contains about 10% nitrogen and makes an excellent fertilizer so you may actually end up with a bumper crop of weeds!Insects
By far, grubs are the biggest insect issue for turf. Grubs are just one stage in the life cycle of many types of insects, including some moths and certain beetles such as Japanese beetles.
We did not experience a huge Japanese beetle outbreak this year here in my part of Crystal Lake. They do seem to be somewhat cyclical, so I am guessing that over the next few years we will see populations build back up. The best time to kill grubs is in the juvenile stage, which is to say mid-to late July. There is also an organic alternative for grub control.
Milky spore is a bacteria that the grubs ingest as they are chewing on the roots of your lawn. The bacteria then kills the grubs. Milky spore comes in two forms– a concentrated powder that you apply with a tube that looks like a giant Parmesan cheese shaker , and a granular form that is not as concentrated but is more easily applied with a drop spreader. It is not an immediate cure as it takes several years for the spore count to reach a critical mass.
Fungi
The most common lawn fungi are powdery mildew, red thread, pink patch and rusts. The University of Illinois does not recommend fungicides on home lawns. Instead use the good horticultural practices that we have talked about. Most fungal diseases occur in shady areas where the grass is not as healthy. Plant appropriate shade tolerant grasses in shady areas, or better yet, replace the lawn with shade tolerant ground covers or a shade perennial bed. Water early in the morning and water deeply and infrequently. Make sure the lawn is healthy through a good fertilizer program. Healthy turf is better able to withstand turf diseases.
