August in the garden: Pay attention to water levels this month

After a busy spring of gardening, it’s easy to start running out of steam in late summer. But the garden still needs care. If weather remains dry, provide supplemental water as needed to plants that were installed over the last couple of years. August is also a good time to catch up on weeding. Look for woody plant weeds such as mulberries and box elders that grow up among shrubs. They can be hard to spot when young but become difficult to remove if they get too big.

General garden care

You can attract more birds to your garden if you plan for their basic needs. These include food (seeds, berries, flower nectar and insects), foliage cover (dense evergreens), water (a birdbath or fountain) and nesting areas with shelter and privacy (trees and shrubs located away from the house or patio). Having a variety of plants is important to birds. Aim for a diverse assortment of food sources and plan so there are plants that flower or fruit year-round. It’s possible to include a good variety of plants and still follow the principles of good garden design.

You can continue installing plants in the summer as long as you pay careful attention to watering during the hot weather. When planting from containers, make sure the plants are moist before you plant. It can be hard to re-moisten a root ball once it is put in the ground. If you hold plants in containers before planting, you will typically need water them daily.

When you plant, dig a wide planting hole — up to three times the plant’s diameter — to make it easier for new roots to move into the garden soil. When backfilling soil around the root balls, make sure you do not leave air spaces.

Most plants you buy are grown in a light potting mix that will dry out more rapidly than your garden soil will. More frequent watering is typically needed until the newly installed plants’ roots grow out into the surrounding garden soil. Cover new plants’ roots with a light layer of soil or mulch to help conserve water.

When you water evergreens planted within the last year or two, apply the water at the base of the plant so the root zone is thoroughly moistened. Densely branched evergreen trees can shed water from rain or a sprinkler like an umbrella, so soil away from the plant may be soaked while the root ball is still dry.

A layer of mulch is especially important for plants installed in late summer and fall to prevent frost heaving. Since they will not have had time to grow anchoring roots, these plants can be pushed out of place by freeze-thaw-freeze cycles in late winter and early spring. Mulch insulates the soil to prevent thawing.

Before treating any plant with an insecticide, it is important to identify the insects you see to determine whether or not the insect really is a problem. Some insects are beneficial and help control other insects naturally. Most insects are harmless to plants.

If you have identified an insect and it is a problem for plants, assess whether the amount of damage it is doing warrants a chemical control. If you decide to try an insecticide, it is important to choose the correct control and use it with the proper timing. Many insecticides will not work unless they are applied at a certain time in the target insect’s life cycle. If a variety of treatments are available, use the least toxic control possible.

Populations of yellow jackets (a yellow-bodied social wasp) build in summer. They are unwelcome visitors to picnics and are particularly attracted to sweet foods and liquids such as soda. Good sanitation — keeping foods and drinks covered — is the best way to minimize wasp problems.

As you work in the garden, watch out for places where wasps and hornets may build nests. Wasps tend to make their nests in the ground or in stone walls. Baldfaced hornets construct large paper nests in trees and large shrubs at head height and above. Paper wasps will build nests under eaves, signs and fence railings and will sting if disturbed. Wasps and hornets are beneficial insects, so control them only if they pose a safety hazard.

Trees and shrubs

Even if you have minimal bed space, espaliered plants can soften large blank spaces on walls or fences. An espalier (ess-PAHL-ee-AY) is a woody plant trained to grow in a flat plane. Traditionally, fruit trees were espaliered against south-facing garden walls. But the technique will work with many shrubs or small trees if they are suited to the site’s conditions.

To train an espalier, choose young, supple twigs and branches and bend them gently to meet the design requirements. Using raffia or flexible plastic tape, carefully tie the branches in place to a trellis or to screw eyes or a wire scaffolding securely anchored in a wall or fence. The ties should be secured loosely so they do not constrict the flow of water and nutrients through the stems. Adjust the ties during the growing season as necessary. Prune out branches that are not growing in the right direction to suit your design. Formal espaliers do need regular attention to keep them looking good.

It is best to remove wire baskets, twine and burlap when planting trees. Plastic twine left around the trunk can girdle and kill a tree as it grows. If you need the basket to keep a loose root ball together, set the tree in place and then cut away the top third of the basket before backfilling the hole.

Trees often are planted too deeply. Look for the trunk flare (where the trunk starts to widen into the roots) when determining how deep to dig the hole. Dig a hole that will place the flare at soil level or a little above; the flare should be visible after the hole is filled. Trees whose trunks look like telephone poles coming out of the ground are planted too deeply. In heavy soils, it is best to plant with the trunk flare a couple of inches high.

Any leaves, needles, twigs or branches from diseased trees and shrubs should be disposed of in the landscape waste to get them out of your yard and avoid spreading an infection. Do not add diseased or infected plant parts to your compost or brush pile.

If the new growth at the tips of your pine’s branches has turned brown, a disease called Diplodia tip blight may be the problem. It is too late to spray fungicides now, as the infection occurs in the spring. Prune out dead tips in dry weather to reduce the spread of infection. Remove all infected needles from the base of the tree and dispose of them.

Some varieties of crabapples are very susceptible to a disease called apple scab. Unless they were treated in spring, they will have lost many of their leaves by August and their remaining leaves will be affected with black and yellow spots. Spraying at this point will not help combat apple scab, but you can help afflicted trees by watering them attentively for the remainder of this year and fertilizing them in fall or next spring. Remove all infected leaves and dispose of them. Consider replacing a disease-prone trees with a cultivar that has been bred to resist apple scab.

Branches that quickly wilt and blacken and whose tips droop in a shepherd’s crook before dying could be infected with a bacterial disease called fire blight. Crabapples, hawthorns and cotoneasters are commonly afflicted with this disease. Promptly prune out the affected branches, disinfecting your pruners between each cut with Lysol disinfectant or a solution of one part bleach to nine parts water. Make the cuts well below the affected area and dispose of the infected branches.

Flower beds

Continue to groom your perennials and annuals in August by removing yellowing foliage and spent flowers. Make note of perennials that have flopped and need staking so you can remember to install supports next spring before the plants actually need it. To prevent your border from looking overgrown, you can gently prune back the more vigorous perennials. Cutting leaves off at the base can reduce the size of the plants without leaving them looking pruned.

Lawn

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

Grass grown from a mix of varieties 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 sun-and-shade mix 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 and debris to create a smooth seed bed. Then gently rake in the seed. Keep the soil moist until it sprouts; on warm days this may require watering two or three times a day. A light layer of compost spread over the soil helps keep seeds and soil moist. Bluegrass takes about two weeks to germinate. Once the grass starts to fill in, you can scale back watering from daily to less frequent deep soakings.

When establishing a lawn by seeding, you can expect weeds to come in before the grass can get fully established. Pull these weeds by hand. Do not use an herbicide on a newly seeded lawn until you have mowed it at least four times.

Check the oil and clean out the air filter on your lawn mower on a regular basis. Recently my mower started running erratically and stopping. It turned out I had let the oil run dry, which could have ruined the engine. Fortunately no permanent damage was done. A clogged air filter also will impair performance. The dust raised when mowing over dry leaves later in fall can clog up the air filter.

ŸTim Johnson is director of horticulture at Chicago Botanic Garden.