Question: First of all, let me thank you for your recent article in the Kenosha News concerning lawn care. I have a lawn which is struggling under intense shade. It has recently responded rather significantly to over seeding using tall fescue grass seed. My problem is this: after overseeding, I have refrained from using weed killer because I felt it might harm the new sprouts. As a result of this, I am developing a significant number of weeds. Could you please give me some guidance in terms of how long I must wait after overseeding before I can spray for weeds? I would welcome any advice you can give me. J.L.
Answer: An herbicide can be applied to weeds in a newly seeded lawn after the third mowing. The best weed control is achieved with spot treatment directly on the weed when it is actively growing.
Now that I’ve answered your question, I feel I should share some information about attempting to grow a lawn under “intense shade”. As you have no doubt experienced, it is very difficult, if not impossible, to grow an acceptable lawn in shade. The deeper the shade, the less likely any type of turfgrass will grow. Fine fescues are the best choice for moderate shade with medium to dry soils because they look and feel like a bluegrass lawn. Tall fescue will grow in similar conditions but usually isn’t recommended because of its coarser texture and clumping growth pattern.
Regardless the type of grass, lawn care is a different in shade because the grass doesn’t grow as fast. Photosynthetic rate is reduced because of the shady conditions so we want to maintain maximum leaf surface. Recommended mowing height is 3 to 4 inches, which is about a half inch taller than a lawn in sun. Because the lawn grows slower, it needs half the fertilizer of a lawn in sun. Use a fertilizer composed of 35 to 50 percent slow release nitrogen and adjust your spreader to half the recommended setting.
Most lawns in heavy shade need annual overseeding in late August to early September. Because most weeds germinate in spring, fall seeding will have less weed competition for the grass seedlings.
Another alternative is give up on grass and plant shade ground covers. Although groundcovers won’t take as much foot traffic as turf grass, many can be walked on.
Barb Larson is horticulture educator for Kenosha County University of Wisconsin Extension. Barb has a Master’s of Science in horticulture from the University of Wisconsin-Madison. If you have a plant or gardening question, email Larson at firstname.lastname@example.org or call her at 262-857-1942.