How to protect trees and maintain garden borders this season

Trees planted in lawns can benefit from a mulched ring to reduce competition with grass roots and to keep mowers and weed whips from damaging trunks. If the tree is small, mulch out to the drip line of your tree. If this is not feasible, extend the mulch as far as you can. Even a 6-inch-wide mulched saucer will help protect tree trunks from serious damage. Do not mound mulch or soil around trunks because it can cause rotting at the base of the tree (and it is unattractive). I see a lot of trees with soil and mulch mounded up against the trunk.

Groom your borders to improve plant appearance and maximize flower production. Gently remove any dried or yellowed bulb foliage since the bulbs are going dormant and have already stored nutrients for next year’s flowers. Many bulbs still have green foliage, so it is best to give them more time to mature before cutting back. Most gardeners I know tend to cut the bulbs back too early. Prune off (deadhead) spent flowers on your annuals and perennials to encourage them to continue flowering. Remove yellow foliage to keep the plants neat and tidy.

If your shrubs have a lot of dead areas on the top and thin growth, look at the base of the shrub to see if there is any new growth flushing up. If the top of the shrub is dead or very thin in its leaf development and there is a good flush of new growth at the base, cut the old stems out now and restart the shrub from the base. That way, the shrub will focus its energy on the new foliage developing from the base. Shrubs benefit from this pruning now even though you will be removing some live branches.

Mowing is one way to control weeds in a large, natural prairie area that is being established in your garden. Native plants typically develop their roots, not their foliage or flowers, in their early years, which gives weeds the opportunity to gain a foothold. Mow weedy areas now at a high height to cut back the weeds and keep them from choking out native plants. In small areas, weed by hand. You can also carefully spot treat weeds with an herbicide.

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