Tips for keeping a healthy garden

By Tim Johnson
Chicago Botanic Garden
Updated 6/16/2013 3:59 PM
  • ash tree woodpecker damage

    ash tree woodpecker damage

  • staff weeding

    staff weeding

Trees planted in lawns can benefit from a mulched ring to reduce competition with grass roots and keep mowers and string trimmers from damaging trunks. If the tree is small, mulch out to the drip line, as far as the branches and leaves extend. If this is not feasible, extend the mulch as far as you can. Even a 6-inch-wide mulched ring can help protect tree trunks from serious damage.

Do not mound mulch or soil around the tree trunk. It is not only unattractive but can cause rot at the base of the tree.

Groom your borders to improve plant appearance and maximize flower production. Gently remove dried or yellowed bulb foliage, since the bulbs have already stored nutrients for next year's flowers and are going dormant. Prune off spent flowers on your annuals and perennials to encourage them to continue flowering, a practice known as "deadheading." Remove yellow foliage to keep the plants neat and tidy.

My definition of a weed is a plant that is out of place. A good time to weed is when the soil is moist -- the roots come out more easily. It's very important to get weeds out before they go to seed. A small hand weeder or trowel is helpful.

Look for tree seedlings such as buckthorn, mulberry and box elder that tend to establish themselves in hedges and in the base of shrubs. They are easy to spot if you look closely because their leaves are different from the rest of the hedge.

In areas where it is not practical to dig out the roots of these weed trees, cut off the top growth and treat the stump with glyphosate promptly to kill the root system. Be careful not to allow any glyphosate spray or drips to touch the desirable hedge plants, because the chemical will kill any plant it touches. Read and follow the label directions.

Damage caused by emerald ash borer is becoming very visible in the Chicago area, with many dead and dying ash trees in home gardens and woodlands and along roadsides. This insect is expected to kill any ash trees in time unless they are treated with pesticides.

If you have ash trees you would like to save, contact a certified arborist to determine whether it is too late to start insecticide treatments. The insecticides will not be effective if the tree is already heavily infested. The treatments will need to be done every one to two years depending on the product you use.

Otherwise, replace your ash tree with a different type of shade tree. I chose to remove the ash trees in my home garden and replace them with other tree species.

The wood of dead ash trees will dry out quickly and cause the trees to become hazards, so it is best have any dead trees removed promptly.

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

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