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Cut those roots the proper way to share your envied plants

Published 12:11am Sunday, August 7, 2011

When gardeners get together and someone compliments a plant, it’s not unusual for the admirer to be offered a “piece” to take home and root. Sharing plants is one of the pleasures of gardening. Getting that piece — or cutting — to survive and grow into a new plant is the challenge.

A cutting is a piece of a plant that is cut off and placed into conditions where it regenerates the missing parts and grows into a new, independent plant. For most plants, the best type of cutting to use is the stem cutting, although some plants are also propagated by leaf cuttings (such as African violet) or root cuttings (such as acanthus). When a stem cutting is taken, it generally has leaves and a stem, and it must regenerate new roots.

Stem cuttings taken from some plants root rapidly and easily, while others are more of a challenge. Success depends on taking the cuttings properly at the right time of the year and providing them with the right conditions for rooting. The cutting must survive until the new roots form.

A common mistake made by gardeners is taking cuttings that are too large. Cuttings should generally be no more than 3-6 inches long. Cuttings that length can be taken from the ends of branches (called tip cuttings), or longer shoots can be cut off and sectioned into shorter cuttings.

The cut at the lower end of the cutting should always be made just below the point on a stem where a leaf or pair of leaves is attached. Take cuttings in the cool, early-morning hours when plant tissue is full of water, and immediately put them in water or wrap them in a moist cloth. Keep the cuttings cool, and plant them as soon as possible.

When preparing to plant the cutting, make sure it isn’t too long and trim it if necessary. Remove the leaves on the lower half of the stem. If the remaining leaves are large, such as is the case with hydrangeas, they may be trimmed to reduce their size by about half — but don’t remove all of the leaves.

Products containing root-promoting hormones are available at local nurseries and should be applied to the cuttings following label directions before planting them. These products are effective in making cuttings root faster and more reliably.

The material, or medium, you plant the cuttings into is very important. A good rooting medium must be loose enough to provide the base of the cuttings with plenty of air, yet retain enough water to keep the cuttings from drying out. It should also be free from disease-causing fungi that could cause the cuttings to rot.

A classic rooting mix is made from one part sharp builders sand and one part peat moss or shredded sphagnum moss. I often use a half-and-half mixture of vermiculite and perlite because these materials are readily available, sterile and relatively inexpensive. Other combinations would work well — even a light potting mix.

Fill a container with moistened rooting medium. Make a hole in the rooting medium, insert the cutting by one half its length into the medium, then firm the medium around the cutting. Several cuttings can be planted fairly close together in a container at this stage. When all the cuttings are planted, they should be watered in.

Cuttings root more reliably in high humidity. To achieve this, place containers in old aquariums covered with glass, or cover pots with wide-mouth glass jars, plastic soft drink bottles with their bottoms cut off, plastic bags or other materials that are clear (cuttings need light). If you use something like plastic bags, keep the plastic off of the cuttings with small sticks (pencils or chopsticks work well).

Place the cuttings in total shade outside or a bright window indoors that does not receive direct sun. Water them often enough to keep the rooting medium moist but not soggy (covered containers may not need to be watered because the covering conserves moisture).

The time required for rooting is variable, depending on the type of plant. Three to six weeks is typical. Check the cuttings periodically by gently pulling on them. When you feel resistance, rooting is under way. Check the root length by gently removing a cutting from the medium about a week or so after you feel resistance. Rooted cuttings are ready to plant into individual pots when the roots are about an inch long.

Plant rooted cuttings into small, individual pots of potting soil. Keep the newly rooted cuttings in the shade for about a week, and then gradually move them into the type of light the plant prefers. You may fertilize it occasionally with a soluble fertilizer.

Many shrubs can be propagated by cuttings taken now. Woody plants require patience when grown from cuttings. It may be two years or more before the plants are large enough to plant in the landscape.

Herbaceous (non-woody plants), such as begonias, impatiens, coleus, many hardy perennials and many houseplants, root easily and quickly from stem cuttings taken anytime they are in active growth.

Be prepared for some failures when rooting cuttings, but consider giving it a try. The satisfaction of propagating your own plants is hard to beat.

Dan Gill is a LSU AgCenter horticulturist.