Gardening with Gary

Gardening Advice from an Expert

Butterfly Bushes

Q. When should butterfly bushes be cut back?

A. Butterfly bushes (Buddleia davidii) are large (even the dwarf ones, reach 8-15 feet) hardy shrubs are highly ornamental and extremely carefree. No landscape should be without at least one. Buddleias are vigorous growers that remain evergreen in winters with minimum temperatures of 20 degrees. Where winters are more severe they can be deciduous, merely dropping leaves, or herbaceous, freezing completely back to the ground. Phenomenal growth is achieved in one season even if they do freeze all the way to the ground.

These large shrubs often give gardeners fits about pruning. It is important to remember is that these are tough plants. There is almost nothing wrong you can do. You can prune anytime. If you prune hard during the growing season, the worst that can happen is you will cut off your flowers for a while. But, they grow fast and you have them again soon. The normal life cycle of this bush is to go dormant in zones 5 and 6. At this point, the canes above ground are dead. They can then be pruned to the ground. This is usually sometime after frost. If you are in a marginal zone 5 area, it is a good idea to apply a 3-6" layer of mulch covering the crown. In zones 7 and up, the bush will remain evergreen and can be pruned to the ground or in any configuration that suits your garden.

Here is an excellent site on pruning of all ornamental shrubs, complete with diagrams. [Pruning Ornamental Shrubs by Christopher J. Starbuck Department of Horticulture, University of Missouri-Columbia]

http://muextension.missouri.edu/xplor/agguides/hort/g06870.htm

The article goes on to supply more information which I share with you: As with most plants we grow, good drainage is important for Butterfly Bushes but rich soil is not necessary. A 2 3/4 inch potted plant placed in the ground in early spring will grow to 3-3' in one year, and as much as 8-10' the following year. This fast growth makes these shrubs perfect for naturalizing vast areas or covering hillsides. They also make quick beautiful covers for fences or buildings, providing quick shade for hot summer spots in the landscape.

They can be grown in large 1/2 wine barrels and trained into long blooming standards or small patio shrubs. In fact, their fast growth makes them a perfect choice for spring potting. Using a 5 gallon pot should be adequate for a season of enjoyment. With fertilization and pruning, they continue to bloom in the pot throughout the summer. By the next spring, they will need to be repotted or planted in the ground.

While Buddleias do require some summer watering, it is not an excessive amount. Once established, as infrequently as once a month can be sufficient. A great advantage is that the scorching sun does not adversely affect their growth nor does it burn their leaves. Even more importantly, the broiling sun does not fade the colors of the flowers. And, after all, the flowers are the main attraction. Millions of tiny flowers are formed along a bottle brush like spike.

Q. Can I propagate a Butterfly bush by cuttings in water?

A. Since you asked, is it possible, then I answer yes. Is it the most desirable method, no. I find the results are best when using a rooting mix and cover the tray or pot with plastic. Here is what I have for you:

Buddleia - Butterfly Bush, Summer Lilac

The best method of propagation, if a greenhouse is available, is to make cuttings in September and October and grow them through the winter in the greenhouse, in which case they will be large blooming plants by Springtime. Outdoors, Buddleias are readily propagated from young spring shoots rooted in sterilized sand or propagating mix, both with perlite. It is a bit difficult to get the young plants through the first winter in severe climates.

One method is to take the cuttings in mid-August, using soft wood cutting 4" long. Apply 8000 PPM IBA rooting hormone and stick in a sterilized soil or soilless rotting mix [with at least 50% perlite for drainage], cover with clear plastic punched with air holes and mist only as needed. It takes about 70 days to root well.

An alternative method is making 4-inch cuttings from the hardwood in the early spring when you trim the bush back and shoots have just sprouted. Keep a few emerging leaves at the top of each piece, strip the rest off the piece, make an X slit on the bottom of each piece with a knife (the roots come out from there), stick in a baby jar of plain water, and most importantly...put the cuttings in jars under grow/shop lights (not a windowsill). Place the light about 3" from the top leaves. Keep lights on at least 14 hrs daily. Change water every three days. In about 3-4 weeks, you'll have rooted cuttings. Pot them in a good fertile, well-drained soil mix, keep moist and under the lights for another 2 weeks.