A couple of years ago I removed an English Walnut tree from my backyard. My lawn is much improved however I have reoccurring bare patches in the same areas even after I have reseeded each spring. I am assuming it is Juglone still contaminating my soil. Is there anything I can do short of sod and soil removal, then reseeding a new lawn?
Thank you for contacting Toronto Master Gardeners.
Both the English Walnut (Juglans regia) and the Black Walnut (Juglans nigra) grow in southern Ontario. The roots of both trees release juglone. However, the English Walnut does not typically release sufficient quantities of juglone to cause toxic reactions in other plants. If you are certain that your tree was an English Walnut, the problem may not be juglone in the soil. If there is a possibility that your tree was a Black Walnut then juglone may well be present in the decomposing roots of the tree that you removed and still persist in the soil. The bare patches may be the result of many factors, but there are several things that you can try to improve your chances of success with spring seeding.
OMAFRA lists several plants that are resistant to juglone including turfgrasses. Some of these include Kentucky bluegrass and fescue. Additionally, white clover is juglone resistant and can be mixed in with your grass seed when reseeding in the spring.
See: http://www.omafra.gov.on.ca/english/crops/facts/info_walnut_toxicity.htm
Since you have had some success in improving your lawn already, I would be reluctant to remove the existing grass. As a starting point, improving the soil would be an easier and preferable option whether or not juglone is present in the soil. Excellent soil drainage will assist in reducing the toxicity of juglone, if present and will provide a better medium for your grass seed regardless. Amending the soil with plenty of compost or other organic matter will aid in drainage so that over time, any juglone will leach away. Additionally, planting more than one kind of seed possibly with the addition of white clover may improve the chances of fixing your bare patches. It is also important to keep the soil evenly moist until water grass seedlings are well established.
Good luck with your lawn!