Summer lilac is one of the most beautiful flowering shrubs in the midsummer garden and attracts numerous butterflies with its large flower corollas. Here is how you can successfully propagate it.
The summer lilac (Buddleja davidii) is undoubtedly one of the most popular flowering shrubs in the garden, and is also extremely robust and easy to care for. It often shows the most beautiful flowers on rather poor, well-drained soils and also copes well with drought. And best of all, it is so easy to propagate that even gardening amateurs can usually do it right away.
How to propagate summer lilac by cuttings?
Propagation by cuttings is the most common method, it is also practiced in nurseries. As starting material, take flowerless, not too soft shoot tips or shoot sections from the mother plant between June and mid-August. Cut off a shoot that does not bear flowers. This will increase the chances that you will get vigorous young plants. Obtain the cuttings from the non-woody part of the shoot. In addition to the head cutting, you can cut several partial cuttings depending on the shoot length.
Starting at the top, separate finger-length sections. With summer lilacs, you don’t need to cut directly under a pair of leaves, as they root well even when cut between pairs of leaves. Use your fingers to pinch off the lower leaves that would otherwise be in the ground later. At the top, leave two to three leaves, shortening them by half to make better use of the space in the seed tray.
Use scissors to shorten the leaves by about half. In this way you reduce evaporation and space requirements of the cuttings. A low-nutrient mixture of two parts seeding soil and one part sand has proven successful as a substrate. Fill the soil into small clay pots, about 10 cm (4 in) in diameter, and place the cuttings in them.
For watering, it is best to use a small watering can for houseplants. Then check that the cuttings are still firmly in the ground. Improvise a mini greenhouse with skewers. Attach three of the thin wooden sticks to the rim of the pot and put a transparent bag over them. Under the cover, the cuttings are protected from drying out. However, make sure that the film does not touch the leaves, otherwise rot will form easily. The high humidity created underneath encourages root development and prevents the cuttings from drying out. When fresh shoots appear, rooting has succeeded and the bag is removed. If you want to put the young plants in the garden bed in the current year, you should protect them from frost damage in the first winter.
How to propagate summer lilac by live stakes?
At the end of the growing season, that is, in late autumn before the frost, cut off vigorous one-year-old shoots from the bushes. Any remaining leaves are completely removed and the branches are shortened to 20 to 25 cm (8 to 10 in) in length. Make sure there is a bud or pair of buds at both the beginning and end. So that you still know where the top and bottom are later, you can cut off the lower end at a slight angle, and the upper end straight.
Immediately after that, the live stakes are put into the ground. Prepare a sheltered, semi-shaded corner of the garden for this by loosening the soil by digging, freeing it from weeds and working in plenty of humus. Insert the cuttings vertically into the ground, right side up, about 15 cm (6 in) apart, so that no more than a quarter of them peeks out. Then water and always keep them well moist. In winter, cover the bed with a fleece in case of severe frost and check from time to time whether the cuttings are still deep enough in the ground.
If you can’t stick the woods right away, they can be placed in bundles in a box or in the garden bed in an excavated hole and completely covered with moist sand. Another way: you put the woods in a foil bag and put it in the refrigerator. In March/April, as soon as it remains frost-free at night, the bundles are dug up or taken out of the refrigerator. The cooled cuttings are then placed in water for a day, after which they are planted as described above.
Already in the coming spring, as soon as the soil warms up, the first roots begin to form. This can be seen when new shoots appear. When these have reached 20 cm (8 in) in height, they are cut back so that the plants become nice and bushy.
How to successfully sow the summer lilac?
Sometimes summer lilacs spread themselves by sowing. However, these offspring do not turn out true to the variety, that is, they bloom differently than the mother plant. Of course, this can lead to quite exciting results. The situation is different with the alternate-leaved butterfly bush/alternate-leaved summer lilac (Buddleja alternifolia), which as a pure species can be propagated well by seed. To do this, harvest the capsules in the fall when they have turned brown-yellow and dried. Sieve the seeds, store them frost-free but cool, dark and dry over winter and sow them in seed soil in March/April.