Garden Detective

Garden detective: A few secrets to multiplying lilacs

I have tried many times to transplant a portion of a lilac bush that I have had in my yard for many years. I have attempted at least three or four times over the years to remove a small sprig and transplant it, but they never take. Here is what I have attempted: In the spring, when it starts to show green leaves, I remove a small branch, wrap it in newspaper and soak in water for several days. I then plant it in Miracle-Gro soil, but to no avail, as they all end up not taking. What am I doing wrong?

Tony Tambini, South San Francisco

Lilacs are not the easiest shrubs to propagate. Kent Thompson of the Sacramento County Master Gardeners tackled your dilemma.

“I recommend a book called ‘Plant Propagation’ by the American Horticultural Society,” Thompson said. According to that informative guide, lilacs can be propagated via softwood cuttings in late spring. Here’s what it says: “Take stem cuttings from 2-inch softwood shoots. With hormone rooting compound, free-draining medium, and bottom heat, rooting takes 6 to 8 weeks.”

The book claims this method is “moderately challenging” with lilacs, Thompson added. It also says starting them from seed is easier.

But cuttings often are easier to obtain than lilac seed. And what do these horticulturist instructions mean for the average gardener?

Always start with a healthy mother plant with strong, green growth and no signs of disease or pests.

Also called “greenwood” cuttings, softwood cuttings come from that vigorous new growth. These cuttings are made from soft, succulent new growth of woody shrubs just as it begins to harden, typically in May through July for most plants. You can tell a shoot at the softwood stage because it will snap easily when bent. The youngest leaves on a softwood shoot have not yet reached their mature size.

A 2-inch softwood shoot is just like it sounds: The stem portion should be at least 2 inches long not counting attached leaves. There should be at least one node – that notch where a leaf was attached – near the bottom end of the cutting; ideally, a cutting should have two or three nodes. Make the cut with a sharp knife or pruning shears at a 45-degree angle (that creates a larger surface area for rooting). Remove all but the top two sets of leaves.

Rooting hormone is the secret to success for rooting cuttings from woody plants. Under various brand names, this hormone is available in powdered form from most nurseries and home improvement centers. Moisten lightly the bottom (cut end) of the cutting and dip that end into the powder so it covers the bottom inch (including that bottom node). Gently shake off any excess powder before putting the cutting into the potting mix.

“Free-draining medium” is the potting mix. Most high-quality potting mixes, particularly those designed for starting seeds or new plants, would qualify as “free draining medium.” Your cutting has no roots, so choose a mix with no added fertilizer. If creating your own free-draining medium, use equal parts clean coarse sand and peat moss mixed with a little perlite and vermiculite.

To keep the rooting hormone on the cutting, poke a hole in the moist potting mix with a chopstick or pencil, then insert the cutting and gently tap the mix around it. Keep the potting mix moist but not wet; don’t let it dry out while your cutting is trying to root.

“Bottom heat” refers to a seedling heat mat or other device to keep the potting mix (and root area) warmer than the surrounding temperature. That stimulates root growth as well as seed germination and can speed up the overall process.

As an alternative, indoor conditions usually are warm enough to stimulate most cuttings to root. (Cuttings such as lilacs prefer temperatures above 70 degrees to root.) Instead of bottom heat, just keep the cuttings indoors, preferably in a warm window (but not direct sunlight).

An extra step that helps in rooting such cuttings is to create a “terrarium” atmosphere, surrounding the cutting with its own mini-greenhouse. Put the cutting and its pot inside a clear plastic bag, closed at the top. Or put the cuttings inside an empty aquarium, covered with glass or clear plastic, and placed in a bright spot.

Once the cutting sets roots, it will start to form new leaves and grow. Then, you can set it outdoors in a protected spot, without its terrarium, until its ready to transplant into the ground.

This method can be used on a wide range of cuttings, not just lilacs. Try it on fuchsias, chrysanthemums and geraniums.

GARDEN QUESTIONS?

Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties. Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h&g@sacbee.com. Please put “Garden Detective” in the subject field and include your postal address.

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