Free Lilacs for Life! — Part 2. How to Root Lilac Cuttings for Advanced…
By: Mark Debard
Tags: Rooting, Cutting, Lilac, Horticulture

Free Lilacs for Life! — Part 2

How to Root Lilac Cuttings for Advanced Outdoor Home Gardeners

S. vulgaris ‘Arthur William Paul’

Would you like a free and unlimited numbers of lilacs? Unlike with seeds, almost all shrubs and perennials can have identical copies made from short cuttings of the stems or branches of mother plants. Some, like lilacs (genus Syringa), are more difficult to root than others.

The best lilacs are taken from named cultivars, or “cultivated varieties.” Here’s a summary of how the advanced outdoor home gardener can root a large number of these free cuttings, with detailed information and pictures following:

1. Choose a lilac cultivar with no active patent.

2. Prepare an outdoor open or closed area with misting or fogging capability.

3. Add rooting medium of coarse sand, with or without peat, potting soil, or perlite.

4. Take 6-inch cuttings from the ends of new green softwood growth in spring.

5. Remove all but the top 4 leaves and trim the base through a leaf bud node.

6. Dip in IBA rooting hormone and plant (stick) 2–3 inches apart in the bedding area.

7. Keep in shade; mist frequently with sprinklers or fog nozzles with a timer.

8. Check for roots between 1–3 months, then transplant.

Legal Cuttings

There are no restrictions for rooting any lilac with one condition: you can’t use lilacs with active patents. This applies to some newer lilac cultivars only. Patents apply to a few generically named cultivars for a limited number of years (20 years in USA); after that, anyone can freely propagate that cultivar. Look for “USPP No. #” or “PPAF” after a name. A plant patent gives the inventor the right to prevent others from reproducing, selling, or using the plant, including sports, mutants, and hybrids whether natural (if discovered in a cultivated area) or induced. USA patents that have been applied for or granted can be found at http://patft.uspto.gov/. It is unclear if USA residents can legally root cuttings of cultivars with foreign patents; it is certainly unethical to do so without the patent-owner’s consent.

Trademarks (™) and registered trademarks (®) do not apply to a specific cultivar, but to a name used by a specific business. These are indefinitely renewable in the USA every 10 years (unlike patents). Unlike in past decades, it is now common to give new cultivars nonsense generic names and catchy, beautiful trademark names.

S. vulgaris ‘Monore’ or BLUE SKIES®, photo by Ole Heide

For these, you can take cuttings of the (non-patented) cultivar, but you can’t use the registered name, only the generic cultivar name. If the generic cultivar name has appeared in print, it can never be changed unless it is illegally named (per international agreements). For instance, S. vulgaris ‘Monore’ is the generic name of a lilac cultivar, while BLUE SKIES® is its registered trademark name. Its patent expired in 2009 so you can take cuttings of this plant and label or even sell it as ‘Monore’, but you couldn’t sell it as BLUE SKIES® since Monrovia Nursery has the exclusive right to use that trademarked name, at least until it stops paying for that trademark.

Propagation Setup

Outdoors is best for a larger number of cuttings due to space and frequent misting considerations. This can be done in seedling trays placed on flat ground that is covered with weed barrier cloth, or in raised beds with a 4–6-inch soil depth. For the hobbyist home gardener, it is suggested the raised bed be a minimum 3x4 foot size using 1x6 boards, or as big as a 4x10 foot bed using 2x6 boards. Larger hoop or greenhouses are more for the commercial nursery. It is possible to do this in the shade with no cover, or it can be done in the sun with a suspended tarp or crop cover for shade.

But lilacs, especially common ones, really like high humidity all the time and do best inside more of a fogging house. To do this, the cuttings area will need to be enclosed.

Enclosed hoop house over an elevated container bed

Fresh cuttings stuck in sand and some potting soil in misting hoop house

Use six-foot hoops across a 2–4 foot width that will then be 2–3 feet high, or longer ones if you want a higher or wider enclosure. Space the hoops 2 feet apart and secure to each other with heavy wire or cord and perhaps rope stakes on the end hoops. Cover the hoops with 4 mil clear polyethylene plastic if placed in a fully shaded area. If in the sun, use 50% transmissive polypropylene shade cloth or translucent plastic. Ventilation of the hoop house will decrease fungal growth but also decrease the fogging effect. The covers also provide protection from wind dispersion of mist. Ten-foot long by three-foot wide commercial plastic hoop houses are available for $70 (Gardener’s Supply Company).

A soilless mix is best to reduce the possibility of disease transmission since garden soil may have spores and pathogens. It does not need to actually be sterile, though some mixes are. For lilacs, good drainage and aeration are essential with a minimum of fertilizer. Do not use vermiculite as it compacts and holds too much moisture. Possible soilless recipes for lilacs include the following:

1. Coarse sand alone. It is also known as paver sand, builder’s sand, and river sand. One can also use sharp angular sand which is also called concrete or grit sand, which has even larger particles. Both types of sand are known as horticultural sand. Do not use play sand, which is finer, washed, smooth and rounded, may have salt in it, and while draining well does not allow aeration.

2. 1:1 coarse sand and perlite.

3. 1:1 coarse sand and peat.

4. 1:1 perlite and peat.

5. A mix of peat, aged pine bark, slow release fertilizer, and lime. The lime neutralizes the mild acidity of peat and pine bark (lilacs don’t like acid soil or rooting medium). The advantage of this formula is that rooted cuttings can be left in place for a year.

Heating and Light:

Heat is not necessary but speeds the process. A hoop house in plastic can have a heat buildup to 90–100°F or even higher in the sun, requiring ventilation. Or a waterproof heat mat can be used in early spring in an open ground setup to keep the potting mix temperature between 70–80°F.

Bright indirect light with no direct sunlight is required to sustain photosynthesis and avoid overheating and water loss, though dappled sunlight may be acceptable.

Late lilac green softwood stem

Cutting Type and Timing

The mother plant from which cuttings will be taken should be large enough that removing cuttings will not stunt, harm, or kill it. Cuttings can root at any stage of a stem’s life, but are easiest in lilacs at the softwood stage: not too hard and thick (which are woody and don’t bend), not too soft and thin (which bend but don’t snap), but just soft and thick enough to bend and snap. In most areas, this will be mid-April to mid-June, depending on the type of lilac. Another measure of ideal softwood cuttings is when leaves on the stem still have a gradation of leaf size where the oldest leaves are mature and new ones are still small.

Fresh lilac cuttings

Cutting Selection

Cuttings should be taken from the current season’s new growth, preferably from high up on a younger plant on a lateral shoot. Cuttings from young plants and high stems root in higher percentages, as they have more regenerative hormones in place. Older, lower, main stem shoots have less regenerative hormones, though the tips of main shoots are acceptable. Cuttings are best taken in early spring after buds form and up until 2 weeks after flowering. Take cuttings from new stems with neither buds nor flowers, so energy is not sapped by flower production.

Clean the cutting tool (usually a pruner, though a knife or scissors would work) in rubbing alcohol or 1/10 bleach solution to prevent transmitting disease. Cuttings should be collected in the morning when the plant is fully hydrated, has the least stress and can be planted the same day. Never crush or squeeze the stem.

Protect the fresh cutting from drying and from the sun, wrapping it in a damp paper towel and placing in a plastic bag. Keep the cuttings cool and shaded until stuck, using a cooler if needed.

Take 2–4 cuttings of each cultivar, expecting to lose some. Since the common lilac is the hardest to root, take at least 4 cuttings for each cultivar; the late lilac is the easiest so take at least 2 cuttings for each cultivar of these. Expect 10–25% of common lilacs and 50–75% of late lilacs to root. Littleleaf and tree lilacs will be in-between.

Cuttings of littleleaf lilac with lower leaves removed and tips trimmed

Cutting Preparation

Cutting length should be 4–6 inches but can succeed with anything from 3 to 12 inches.

Long shoots can be divided into several cuttings. Leaves should be stripped from the lower half of the cutting to reduce water loss and conserve space; the lowest stripped leaf bud is where the roots will form.

Some leaf surface should be left to continue photosynthesis since no food will be moving from the as-yet nonexistent roots. However, too much leaf surface saps energy from the rooting effort and loses excessive moisture through transpiration loss. Leave between two leaves cut horizontally in half, to two pairs of intact leaves. Another reason to cut some leaves in half is that leaves could be particularly oversized for the small cutting (especially in the late lilacs) and lead to bending or rubbing against adjacent leaves of other cuttings, increasing the risk of disease. If all the leaves drop before rooting occurs, the cutting will not succeed as it will have no food from photosynthesis, in which case it will need to be discarded.

All of this suggests that four leaves cut in half are better than two leaves left whole. Cut the base of the stem just below or through the leaf bud, either horizontally or diagonally. Wounding or crushing the stem is not necessary and may be harmful.

Rooting Hormone Treatment

Plants have natural hormones that promote rooting, called auxins. A synthetic auxin, indole-3-butyric acid or IBA, can do the same thing. It is available in multiple concentrations. For lilacs, which are hard to root, a moderately strong concentration between 0.3–0.8% (or 3000–8000 parts per million) powder in a talc base (which causes it to stick), or a similar liquid, is the preferred method of stimulating rooting. Higher concentrations or excessively large amounts of IBA can be detrimental to cutting health and should not be used. Lower concentrations will decrease the number of cuttings that successfully root.

Cutting base dipped in IBA rooting hormone ready to stick in dibbled hole

Pour the powder or liquid from its original container into a separate clean container to avoid contamination of the original container. Dip the bottom 1 inch of the cutting in the liquid, or wet it and dip in the powder, shaking off any excess. It is also possible to apply IBA as a foliar application spray. Wounding the base of the stem to promote the uptake of IBA and hasten rooting may be harmful due to disruption of the phloem and xylem (the food and water channels in the stem which form the vascular bundle).

Sticking the Cuttings

Cuttings (coated with IBA) should be planted (stuck) in the rooting medium as soon as possible. Use a dibble (like a pencil or clean stick) slightly larger than the cutting’s diameter to make a hole so the rooting powder is not knocked off on cutting insertion.

Insert the cutting 1.5–2 inches deep, or 1/3 to ½ the length, with 1–2 stripped leaf nodes below the surface, while maintaining its proper vertical orientation. Tamp down the rooting medium to hold the cuttings firmly in place and then water and mist them. Space the cuttings about 2–3 inches apart, so their leaves don’t touch anything.

Misting and Watering

Since they have no roots, cuttings get their water (and food) from the remaining leaves. The leaves get water from the surrounding air or leaf surface, hence the need for frequent misting and high humidity until rooted. Keep the soil moist but not soggy.

AC solenoid water valve with calcium filter and pipe to hose converter

Automated misting will be necessary outdoors or for larger numbers. An inexpensive setup can be easily built by the home gardener. You will need either PVC pipe or garden hoses and in-line particle ($8–14) and calcium filters ($14–25) to reduce impurities that clog the sprinklers or misting nozzles. A permanent magnetic hard water conditioner could be used in place of a calcium filter ($80).

110/24VAC converter/propagation timer

You will also need a 110AC/24VAC converter/timer with propagation settings for seconds and minutes ($100, can also use for seed propagation), along with a 24VAC normally-closed 2-way ¾” solenoid water valve ($23) with a male ¾” pipe thread to male garden hose converter. Similar battery-operated, DC equipment is available for locations distant from an AC power source. A reliable source is Dripworks that sells Galcon timers and valves.

Open raised container bed with new and old cuttings, shade cloth, and 2-foot tall misting sprinklers

Closeup of misting nozzle on sprinkler

Finally, this can be hooked up to either fine-nozzle, 6 to 18-inch-tall misting sprinklers (also called micro irrigation adjustable sprinklers, 50 small ones for $10) in an open setup, or to a pre-made ¼ inch misting line with nozzles cooling system ($20–35) suspended over the cuttings in a hoop house or a shade cloth setup. You will need 2 parallel mist lines if the cuttings area is more than 3–4 feet wide.

A minimum of 30 psi water pressure is needed; most homes have a minimum 60 psi, but it can be measured with an inexpensive hose outlet pressure gauge ($15). This outdoor setup must be drained in winter.

Sprinkle, mist, or fog from 6 seconds every 30 seconds for an open area, to 15 seconds every 10 minutes for a more enclosed one. Very fine misting or fogging nozzles could even be used continuously in an enclosed hoop house for common lilacs which like water in the air but not on their leaves for a true fogging, high humidity effect.

2-month-old cutting with new roots

Rooting Time and Checking for Roots

Fresh cuttings may look wilted the first week but should perk up after that. Common lilacs take twice as long to root as late lilacs. Expect common lilacs to root over 2–3 months, and late lilacs to root over 4–6 weeks. At those times, pull gently on the cutting’s stem; if rooted, you will have complete resistance and it can then be dug out.

Remove any molded or fallen leaves, dead cuttings, or cuttings with no leaves. Cuttings with no leaves will not root. After successful rooting, remove the humidity cover or transplant the cutting.

Post-Rooting Care

After rooting, stop misting and water the rooting medium only when the soil dries out. There are two good ways to proceed. The first option is to leave the cuttings in the rooting bed through winter, perhaps covering with straw. Then in spring they can be “lined out” in the garden, 10 inches apart with 30 inches between rows, or transplanted.

Rooted cuttings in pots shortly after transplanting to quart pots

The second option is to transplant immediately or later in the early fall. If done immediately, put into small 3–4-inch diameter quart pots. Fill the pots with ½ potting soil and ½ coarse sand or 75% potting soil and 25% perlite (by volume) and insert the roots 2–3 inches deep. A long-acting fertilizer can be added. Then place the pots in open or dappled shade until new leaves form (a great sign), roots come out the drainage holes, or cooler temperatures arrive in the early fall.

12-week-old late lilac cutting transplanted to one-gallon, 6-inch container

At that time, transplant the rooted cuttings left in the original rooting medium or the ones that had been transplanted into the quart pots to one-gallon containers and place in the sun. Late lilacs can usually be transplanted and put in the sun sooner.

After leaves are lost in late fall, place the container in a protected area for winter, such as against a building or inside an unheated or heated space. Container lilacs will survive winter outdoors with temperatures to 0°F with no problem.

After the first season of growth, prune your new lilacs back in spring to 2–4 inches above ground to induce branching. They can then be planted with good protection from animals, or held another year or two, planting before they reach 3–4 feet in height. Don’t forget that they take 3–5 years to flower.

Enjoy your free lilacs!