University of Maryland Extension

March Tree and Shrub Tips

pussywillow catkins

(More tips from HGIC)

  • For a bright vase of color indoors, the prunings of spring flowering shrubs can be brought in and placed in water to force early blooms. Forsythia, pussy willow and some blooming ornamental fruit trees work well for this.
  • Non-flowering trees and shrubs can be pruned before new growth and when the worst of the winter weather is over. Remove branches broken by winter weather, prune out dead or diseased branches anytime and make any necessary cosmetic cuts. It is not necessary to paint pruning wounds. In fact, wound dressings will impede the natural healing process. (PDF HG 84 Pruning Ornamental Plants). You may notice excessive sap bleeding from pruning cuts on elm, maple, birch, dogwood, beech, walnut, magnolia, tulip poplar and redbud. This bleeding is harmless to the tree. If you want to avoid the “bleeding” wait until these trees have leafed out before pruning.
  • Heavy pruning of healthy twigs and branches of spring flowering shrubs (azaleas, rhododendrons, forsythia, etc) at this time will reduce the number of blooms this spring. So if this is of concern to you, wait until after flowering before doing heavy pruning. To rejuvenate older, multi-branched shrubs, remove only 1/3 of the oldest wood to prevent removing all flowering/fruiting branches at once. If, however, heavy pruning is necessary, the best time to do it is right before new growth begins.
  • March is the beginning of the planting and transplanting season for woody landscape plants. Avoid working with wet soil; wait until the soil dries out. Common planting mistakes include planting in compacted or poorly drained soil, planting too deep and buying damaged plants with poor root systems.  When properly planted the staking of new trees is usually not necessary. However, occasionally high winds and soft, saturated soils can lead to the tilting of young or newly planted trees. Simply pull these trees upright and gently tamp the soil down over the root system.
  • Roses can be pruned starting in mid-March to maintain their shape and size. Roses always have some winter kill; to determine whether or not a branch is alive, simply scrape the bark with a sharp knife and look for green tissue.
  • Refrain from any hard pruning of vines like clematis until you can determine which vines are alive and which have been winter damaged. Waiting until mid to late April will help you better determine what needs to be removed.
  • Remove and destroy bagworm bags from affected trees (primarily needled evergreens). The bags contain hundreds of eggs that will hatch out and feed in the spring. Discard or destroy the bags- don’t just leave them on the ground. (PDF HG 32 Bagworms)
  • Hemlock wooly adelgids are aphid-like sucking pests that appear as white, waxy masses on the needles of hemlock trees. Heavy infestations can debilitate trees, particularly when they are stressed. Spray trees with ultra-fine horticultural oil when the crawlers are out in late May or early June. Infested trees can be treated with imidacloprid as a drench around the base of the tree – follow all label directions and precautions. Do not fertilize Hemlocks. Research has shown that increased nitrogen may actually increase adelgid populations on hemlock. (PDF HG 2 Hemlock Woolly Adelgid)
  • The tiny reddish-brown eggs of spruce spider mites can be seen with a hand lens on the twigs and needles of spruce at this time. If you notice signs of this pest, apply an ultra-fine horticultural oil spray which will smother and kill the eggs. (PDF HG 13 Spider Mites)
  • Inspect trees for gypsy moth egg masses. They are tan colored, felt-like and 1-2 inches long, and may be found on tree bark, firewood or any outdoor, wooden structure.
  • Inspect trees for the egg masses of the Eastern tent caterpillar. They resemble black Styrofoam and are usually found on the ends of cherry and crabapple tree branches. Both types of egg masses should be removed and destroyed. The eggs of Eastern tent caterpillar will hatch out when cherry tree leaves unfold. They create white silken web nests in the branch crotches of these trees. If your trees are heavily infested, you can control them with a spray application of the microbial insecticide, B.t. later this spring when they have all hatched out but still small. (PDF HG 21 Eastern and Forest Tent Caterpillar
  • If you had a problem last year with scale insects on woody landscape plants spray them with a dormant oil prior this month to bud swell. Spray on a dry day when temperatures are above 40 degrees F. and are expected to remain above freezing for at least 24 hours. March is the last time you can apply oil at the dormant rate because the dormant rate can burn green tissue, so if you notice bud or leaf growth, spray horticultural oils at the summer, 2%, rate. Dormant oil is an environmentally safe product to use and is very effective in controlling scale insects.
  • Prune out black knot cankers on flowering cherry and plum trees and cedar apple rust galls on cedar trees. 
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