With all of the hectic days of planning and planting behind us, June is a great month to focus on pruning and propagating shrubs. Correct timing and technique are critical to ensure the health of your plants.
Hedges of Japanese holly, yew, and privet can be shaped and trimmed of their first flush of spring growth. As with all evergreens, such pruning must be done before mid-July to give the plants plenty of time to put out new growth and mature before heavy frosts occur. Evergreens can be pruned at almost any time other than late July, August, and September. For hollies, wait until December and bring the cuttings inside to enjoy during the holidays.
Flowering shrubs such as old lilacs can be pruned to encourage blooms next year. Lilacs should be cleared of all dead and diseased branches and if the plant is crowded in the center, old stems should be cut at the soil line to let light and air into the plant. Azaleas, mountain laurel, rhododendrons, and andromeda should be trimmed within two weeks—but no more than one month—from the end of this season’s blooms, before the flower buds are set for next year.
June is also a great month to propagate deciduous shrubs like spirea, lilac, forsythia, and viburnum. Take four- to six-inch cuttings early in the day, before the plant is stressed from the heat of the mid-day sun. Place the cuttings immediately into water, then proceed to strip off the lower leaves and dip the cut end into rooting hormone. Choose a well-drained planting medium such as vermiculite and peat moss, or perlite and peat moss, and use in planting containers that are at least two inches deep with draining holes.
The key to successful propagation is to maintain an even level of humidity while the cuttings take root. Create a tropical environment by covering the containers with plastic (but do not let the plastic touch the cutting). Within six to eight weeks, the cuttings should be sufficiently rooted and can be acclimated to ambient temperatures and repotted into larger containers.