March in the garden: March is the month for gardeners to get excited

Even though the winter has been an easy one, there is still a lot of work to be done in the garden before spring. Focus on finishing dormant pruning and spring cleanup before the plants’ growth gets too far along. Fortunately, March is a month when the enthusiasm and optimism of gardeners is high, so getting out in the garden is generally a priority.

Shrubs and trees

Most evergreens will not respond well to being aggressively cut back. A good rule of thumb is to avoid cutting beyond green foliage. Yews, though, will respond to more drastic pruning that cuts back into old wood. But be patient, as it may take two to three years for the plant to fully fill back in. Consider how long you are willing to wait for the shrub to look good again; you might reduce the plant more gradually over a few years until you reach your goal. For best results, complete any pruning before the new growth begins in early spring.

March is a good month to control insects such as magnolia scale with an application of dormant oil. Dormant oils can be very effective with minimal impact on the environment when used properly. Before using any controls, however, verify that you have a problem insect. Avoid applying treatments just to make sure there will not be insects present.

When you apply dormant oil, the temperature should be at least 40 degrees with no chance of freezing or rain within the following 24 hours. Avoid spraying on windy days to prevent any drift of the spray. As with any product, be sure to read the label to make sure the plants you are treating will not be damaged by dormant oil.

Monitor broad-leaved evergreens such as boxwood, rhododendron and holly and needled evergreens such as yew and arborvitae for winter burn. Winter burn is the term for dried-out leaves on plants that do not lose their leaves over the winter. The leaves turn yellow and then brown in response to specific weather conditions. Salt spray from vehicle traffic can also damage foliage. Symptoms of winter burn typically appear in late winter and accelerate in early spring.

Various conditions combine to cause leaves to dry out. Mild winter temperatures and warm winter sun prompt leaves to process water, which cannot be replaced if the ground is either frozen or very dry. Winter winds also contribute to the problem. Winter burn is common after extremely cold and extremely mild winters, and in both cases it is exacerbated by lack of snow or rain in combination with strong winds and abundant sun.

It is usually best to wait until new growth appears before pruning out damaged areas if you are not sure whether or not the sections are completely dead. I have seen boxwood with an overall brownish cast in very early spring that completely greened up later in the season. In general it is a good idea to plant broad-leaved evergreens where they will have some protection from winter sun and wind.

When pruning large limbs from trees, it is a good idea to make an undercut first. This is a cut from the bottom up, about one-third of the way through the limb, 4 inches or so away from the main trunk. Its purpose is to make sure that when the branch falls, it does not split or tear and damage the trunk. To remove the limb, cut from the top an inch or so outside the undercut. The weight of the branch will snap it off at the undercut. To remove the stub that remains, do not cut it flush to the trunk but just outside the branch collar at the base of the branch. Look for the point where the branch is enlarged close to the main trunk of the tree. Use a sharp saw to make a clean wound. It is generally not recommended to paint the wound.

General garden care

Cut back perennials and clean up garden debris this month. It is best to cut back perennials before they start growing to minimize any possible damage to the new growth. It can be hard to see new growth on ornamental grasses, so be sure to cut them back before consistent warm weather sets in late in the month. If the weather continues to be warm and the grasses are growing, then cut them at a few inches above the ground to avoid harming the new shoots. Be careful of any bulbs that may have started growing.

Gently press back any perennials that have heaved out of the ground over winter. There is a greater chance of frost heaving in March. The freeze-thaw cycle in spring can push recently installed plants out of the ground if they were not mulched the previous year. I prefer to stay out of the garden when soil conditions are wet to minimize soil compaction.

Don’t forget to clean bird feeders periodically, as moldy seed can make birds ill. Remove old seed and debris and then scrub the feeder with a solution of one ounce of bleach per gallon of water. Rinse well and allow the feeder to completely dry before adding new seed.

It is a good idea to shake out hanging feeders when refilling them to dislodge any compacted seed. Between more intensive cleanings, dump out wet clumps of old seed and sweep hulls off platform feeders. f possible, provide a source of water for the birds. A heated birdbath is great for periods of freezing weather. Purchase one with an automatic shut-off valve or heat cycling on-off switch, which will prevent damage to the birdbath if it goes dry. Connect the heater to a grounded, three-pronged outlet.

Avoid birdbath heaters that have an uncovered heating element as this, could burn the birds’ feet if they land on it. Placing a flat piece of shale over the heating element (even a covered one) will provide a warm rock for birds to perch on to rest or drink and will prevent any accidental injury.

Houseplants

Prune houseplants as needed and start fertilizing them as they begin new growth. Rotate your houseplants so that each side receives an even amount of light, for more uniform growth and a balanced shape. As the sun strengthens, some plants, such as African violets, may need to be moved away from a south-facing window to avoid leaf scorch.

Make a focused effort to remove any spent flowers, dead leaves or branches, and any yellowing leaves. Remove the dust from the leaves with a kitchen sprayer or by gently wiping them off with a moist cloth. This is a good time to repot plants if needed.

A white or yellowish crust near the drain holes of the pot or at the base of the pot indicates a potentially damaging buildup of salts from either fertilizer or a hard water source. Damage symptoms include brown leaf tips and margins. A thorough flushing with water is needed to get rid of the salts, so flush out the soil with the plant outside or in a sink.

If you have kept a coleus as a houseplant, you can still start cuttings for transplanting to the garden. Use a sharp, clean knife or a pair of pruners to cut the stem just below a leaf node. Remove the lowest leaves, dip the cut end into a rooting hormone and insert it into some fresh, sterile potting soil. The cuttings will also readily root by placing them in a glass of water. Transplant to a pot with growing medium once a small mass of roots has developed. The plants will be ready to use in the garden by the middle of May when the danger of frost is past. Gradually acclimate the coleus plants to the outside environment by increasing the time the plants are left outside over a period of a week or so. Be sure to avoid direct sun at first so the leaves do not burn.

ŸTim Johnson is director of horticulture at Chicago Botanic Garden.