Time to get your lawn in better shape

Mid-August to mid-September is a good time to seed bare spots in your lawn. Choose a seed mix that is appropriate for the amount of sun in your yard.

Grass grown from a mix blended for shade can look different from grass from a mix blended for sun. If your yard has adjoining areas of full sun, shade and partial shade, use a single mix of grass varieties for both sun and shade to give the lawn a uniform appearance.

Prepare the site for seeding by removing weeds and loosening the soil. Low areas will need additional topsoil. Rake out large clods, stones or debris to create a smooth seed bed.

Scatter the seed and gently rake it in. Keep the soil and seed steadily moist until the seeds germinate; for bluegrass, this takes about two weeks. On warm days, you may need to water two or three times. A light layer of compost spread over the soil will help to keep seeds moist.

As the grass sprouts and begins to fill in, shift to watering less often but more deeply.

When establishing a lawn by seeding, you can expect weeds to come in before the grass can get fully established. Do not use an herbicide to control weeds until the grass is sufficiently tall and thick that you have mowed it at least four times. In the meantime, you can pull weeds by hand.

Monitor your garden for plants that need extra water in late summer. July and August have been warm and mostly dry, so some of your plants might benefit from watering.

Focus on plants that have been planted over the last three years or that are showing signs of drought stress such as wilting leaves and color changes in the foliage. It is a good idea to check the soil, though, to make sure the problem really is being caused by dry conditions. Dig down a few inches with a trowel to see whether the soil is dry.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.