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Layering is a passive form of propagation. Certain species will layer on their own. And while there are many different layering techniques, they all follow the same fundamental concept: A stem is encouraged to form its own roots while it’s still attached to the parent plant.
In simple layering, a low branch is bent down to the ground. You can place a stone on top to hold it in place. For many species that are easy to root, this is enough. For more difficult species, you can tie a twist-tie around the stem. The wire will restrict growth as the stem expands through the growing season. After the wire is tied around it, the branch will feel the stress and be encouraged to throw down its own roots. You can also wound the stem by scraping it where it’ll be in contact with soil. This wounding will encourage callus tissue to form, which will then develop into roots. Some growers dust the wound with rooting hormone to increase the chance of success.
Simple layering may be done with a weight on top of the soil, or a stake to hold the branch in question underground.
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Instead of bending down a single branch, in mound layering you’ll pile dirt or old sawdust over a whole bush. You can also turn a tree into a “bush” of saplings, or encourage a bush to grow more stems, by cutting the whole thing to the ground in the winter.
When mound layering, you should replenish the growing medium around the stems at least a couple of times throughout the season, as it’ll settle quite a bit.
Mound layering involves heavy pruning, followed by burying the center of the plant.
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This is where just the tip of a stem is buried. Certain species naturally tip-root, and these are the ones this technique is best for. You can encourage more tip-rooting than the plant would naturally do by weighing the tips down with stones. You can also allow grass to grow fairly thick around tip-layering plants. The grass will help the stems stay in place on windy days or when brushed past by people or animals.
Plants that produce runners need no encouragement to propagate vegetatively.
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You can encourage a plant to make more stems for tip layering by pinching back the tips of stems in early summer. This will cause the stem to branch out, and each branch can create another rooted plant.
Some naturally tip-rooting species include black raspberries, blackberries, gooseberries, and forsythia.
Serpentine, or compound, layering works best on vines and some very fast-growing shrubs. As a layered stem is rooted and continues to grow, the next section of growth is buried, and so on. I’ve had individual goji berry stems layered 6 to 8 times in one season.
Goji berries lend themselves well to serpentine layering.
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This is a very time-consuming technique, but it’s especially useful if you really want to have a tree on its own roots. It makes sense to grow certain trees on their own roots and not grafted for lots of reasons, but especially if you want to build stool beds with them.
Air layering works well for woody plants that would otherwise be too rigid to layer.
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To air-layer, you’ll need to bring the soil up to a branch that’s too high to bend to the ground. First, wound the stem heavily (many growers peel off an entire section of bark). Take a plastic bread bag and cut the bottom out so that you have a sleeve of plastic. Slide it over the wounded stem. Tie the bottom tightly with a twist-tie. Fill the bag completely with moist growing medium. Many growers use peat moss, coconut ﬁber, or old sawdust. Close the top with another twist-tie. Shade the bag by wrapping it in either aluminum foil or burlap, so the roots don’t get too hot as they grow. Check back every few weeks to see if roots are pushing against the sides of the bag. Once they are, clip out the stem and you’ll have a very large, rooted plant.
Stool beds are where plants are grown just to be layered. They’re cut down to the ground every year as layers are harvested. It makes for a simple, effective propagation technique.
There are two methods I use for starting a stool bed. One is to plant trees horizontally. The second is to plant a tree and cut it down in the dormant season to turn it into a bush (this is the same as mound layering, but in this case you’re building a whole bed). With either method, your goal is to have an entire bed sending up a dense stand of shoots.
When trees are planted horizontally, the trunk and branches are laid along the ground, just at or below the soil surface. All of their buds will grow skyward. As the stems grow, pile old sawdust or soil on them until just the tips are showing. I do this three or four times in summer. The stems will root into the medium you pile on. You can think of this as similar to hilling potatoes. Just keep piling medium onto the stems, leaving the tips exposed. In fall or the next spring, simply cut out the stem with some roots attached.
After you’ve harvested the rooted layers off a stool bed, feed the soil with compost or some nutrient-rich mulch. As the years go on, stool beds develop amazing soils and excellent growth. The roots of the mother trees just get bigger and more mature, while the soil is constantly fed by incessant mulching.
Most commercial apple rootstocks are grown in stool-layered beds. Millions of trees are produced this way, at a rate of around 60,000 rooted stems per acre.
You can harvest rooted stems anytime. I like to let them get quite strong before I cut and dig them out. Sometimes I leave stems to root for two or three years before separating. The resulting plants can be huge.
Some plants take only a month or so to form roots, but others require two years, and still others may never do it. It’s ﬁne if it takes a while. Layering requires almost no energy on your part once you’ve started it.
It’s preferable to harvest layers while they’re dormant plants. A pair of pruners or loppers and sometimes a shovel are all that’s needed.
All my stock plants for layering grow stronger every year and send up bigger and more numerous stems each season. I feed them generous helpings of compost and mulch. Layering is slower than using cuttings, but also much easier. Watering needs are near zero with all the mulch. I think layering is one of the most overlooked, easiest ways to propagate lots of plants. If you do it intensively, it can be quite productive and proﬁtable.
Akiva Silver owns and operates Twisted Tree Farm, a homestead, nut orchard, and nursery near the Finger Lakes region of New York. He grows around 20,000 trees per year that are raised naturally without synthetic fertilizers, pesticides, or herbicides.
This excerpt is from Akiva Silver’s book Trees of Power: Ten Essential Arboreal Allies (Chelsea Green Publishing) and is reprinted with permission from the publisher.