Issue: May 14, 2005
Can I grow lilacs from pieces of stem that I cut off after the lilacs finish blooming?Answer:
I usually discourage people wanting to propagate (increase) lilacs by cuttings, but there is a chance to succeed when you do it at the time you propose. However, you should realize that growing lilacs from cuttings is very difficult.
The new, very tender growths may be removed from the plant soon after growth begins. My resource says that there is a very narrow window of opportunity for taking the cuttings from the plant. This time is when the new growths have reached a length of 4 to 6 inches. If you wait much longer, the chances of success (already limited) become much reduced.
These very tender cuttings should not be allowed to dry before or during the rooting process. Treat the cutting with rooting hormones (indolebutyric acid is recommended at a rate of about 0.8 percent in talc) by dipping the freshly cut end of the cutting into water and then into the talc containing the hormone. Immediately place that cutting into a prepared hole. (Prepare the hole before inserting the cutting so that the talc is not rubbed off.) Firm the moist potting soil around the base of the cutting after it is inserted. Repeat this process with many cuttings so that there is a chance that one or a few will succeed in forming roots. It may take 6 to 8 weeks for roots to form.
During the period of rooting, the cuttings must not be allowed to dry. Since they do not have roots to absorb water, high humidity must be maintained around the cuttings. This may be achieved by several methods. Advanced gardeners and commercial plant propagators will place the cuttings in a mist propagation bed in which a fine mist is frequently sprayed over the plants to maintain humidity. A cold frame, shaded to provide bright, filtered light, may also be used. Care must be taken to maintain humidity during the time that the cold frame is vented to prevent overheating.
Light is important, but too much light can cause excess drying. Row cover material or cheese cloth placed over the cold frame glazing will help reduce heating while still allowing sufficient light for the leaves to photosynthesize. The foods produced by photosynthesis are necessary for the formation of roots.
Gardeners familiar with plant propagation by means of cutting often use "hardwood cuttings" that have completed growth at the end of the growing season. This method is not recommended for lilacs. In many instances, lilacs are grafted. Grafting is much more successful than propagation by cuttings.
Another method of propagation that is useful for lilacs that are not grafted is to dig suckers from around the base of the plant and replant them. These suckers are sprouts that developed from the roots and have formed their own roots. This is perhaps the easiest way for most homeowners to propagate lilacs.
Send gardening questions to Southwest Yard and Garden, Attn: Dr. Marisa Thompson at firstname.lastname@example.org or at https://www.facebook.com/DesertBloomsNM/. Please include your county Extension Agent (aces.nmsu.edu/county) and your county of residence with your question!
For more gardening information, visit the NMSU Extension Horticulture page at desertblooms.nmsu.edu.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505-865-7340, ext. 113.