Most spreaders can be easily propagated for transplanting, potting up, or passing along to friends by using at least one of three methods:
• Division: splitting plants into smaller pieces, each with its own root system. This method works with well-established (at least two-year-old) rhizomatous, stoloniferous, and clump- or mat-forming perennials. Division is also a propagation option for perennials and shrubs that produce offshoots or suckers.
• Layering: encouraging adventitious roots to form by placing healthy growing cells in contact with soil. Plants with stems that are flexible enough to be bent and pinned to the ground without snapping are ideal candidates for layering.
• Sticking root cuttings: taking pieces of plants’ roots and reburying them so they will sprout new shoots. Try this with plants capable of self-propagating the same way—by producing colonies of new shoots from their roots and rhizomes even when pieces have been severed from the parent plant.
Division
Division is the most convenient propagation method for filling gaps in new or existing garden beds. Provided with a little water (and shade if you divide during a sunny heat wave), transplants will settle in quickly and take off, only to need dividing themselves soon enough. In fact, most perennials—whether we or our friends want extra pieces or not—require dividing every two or three years to maintain optimal health and vigor. Otherwise, as new growth circles outward from weakened centers, bloom production begins to slow and plants ultimately look wretched. Division is also necessary to keep any growing garden from becoming overcrowded.
The best time to divide most plants is during the early spring (before the forsythia and daffodils have bloomed their hearts out) because any plant at the start of its growth cycle will be just as happy to start growing elsewhere. This time of year is also easier for division because we will have already cut off stalks and seedheads that could poke us in the nose as we work, and new growth won’t yet be up enough to get in the way of our feet. And we can usually count on spring’s gentle rain and moderate temperatures to help give plants the transitional care they need before summer’s heat arrives.
The exceptions to the divide-in-early-spring rule are the plants that bloom before the summer solstice, such as irises, peonies, woodland and moss phlox, and euphorbia. Divide these and other early-spring bloomers in the fall to give them the winter to settle in and perk back up for their show. (Mulch their crown to help prevent frost heaving during winter’s freezes and thaws.) And of course, rules are made to be broken. If you offer plants plenty of water (and shade if they wilt) and if you trim any lush top growth that would tax a reduced root system, you can divide and transplant anything any time you feel the need. Plants might limp along after surgery but they’ll be right as rain next season.
To help prevent transplant shock, water your garden before getting started (particularly if the soil is dry and dusty) and then wait for a few days to give plants a chance to absorb enough moisture.
Dividing rhizomatous or clump-forming perennials
Unplant by digging around the perimeter with a spade, and lever the clump out gently as you get underneath it. Try to keep the root zone intact and full of soil while loosening the crown of the plant like a tooth. Listen for the satisfying pops and cracks as it comes free. If the plant is really heavy, leave it in its hole. If you can lift it without putting your back out (always use your thigh muscles), place it on a clear patch of ground or on the lawn.
An early-spring cartful of hakonechloa divisions.
Choosing a midline of a hakonechloa, a rhizomatous perennial.
Using the leverage of the forks to force halves apart.
Two easy pieces. The one on the left is big enough to split again.
Some plants, like lamb’s ear (Stachys byzantina) and low-growing groundcovers, will easily tease apart with deft fingers, like loosening a knot from a skein of yarn. But the majority will require a little more elbow grease. The first step is to make an eyeball assessment of the diameter and find a midline. Sometimes an obvious gap is present in the center, in which case separating any portion of the remaining donut will be beneficial for the whole plant. If it hasn’t abandoned its center it can be harder to discern where to slice.
Take your best guess and insert two sturdy digging forks, back-to-back along any seam (even if it’s invisible). Push the forks into the roots—sometimes this requires the force of a jump to make the tines penetrate. Use the leverage of the two forks, forced apart, to separate clumps. If the root mass is extremely dense, sever it into pieces using a sharpened spade or a handsaw; cut any joined stems with sharp pruners. Transplant the healthiest pieces, water all of them in, and baby them as if you spent a fortune, which, in a sense, you did if you reckon your time and sweat.
Staking a claim to a mat of oregano, a perennial mint family member that spreads radially.
A tidy clump remains after removing the unwanted sections.
Dividing mat-forming perennials
Unplanting isn’t always necessary when dividing perennials that form a carpet of growth because any portion can be removed without much disruption to the rest of the plant. Eyeball or mark the part you want to keep, then slide a spade into the mat outside of your markers and dig the extras out in pieces. Fill soil in around the remaining chunk and water well. If the best-looking growth is not where you want it, dig out the entire plant and transplant the healthiest-looking sections.
Dividing suckering shrubs
If shrubs have sent up new suckers from roots, dig around to find where they are attached. Then sever their root connection to the parent plant with pruners or a sharp spade leaving 1 to 2 feet of root attached to the new division. Sometimes the root will extend from the sucker or shoot in a T, on its way to forming another. Pull all of that out if you do not want another plant to form (even separated from the original parent, that root should be capable of sending up new growth). Slice that root again 1 to 2 feet from your new plant. Suckers do not always have fully formed feeder roots of their own, so after transplanting, keep them well watered at least until they settle in and begin to grow.
To increase a sucker’s survival rate, sever the connection to the parent plant in summer or early fall, but let the sucker remain where it is while it produces its own feeder roots. Wait until the following spring to transplant the sucker.
Oakleaf hydrangea (Hydrangea quercifolia) suckers are easily separated from the parent in early spring before they leaf out.
Dividing perennial plantlets and offshoots
from stoloniferous shrubs
I am helpless to resist plantlets that have formed at the ends of stolons. If plantlets and offshoots have been in contact with soil and are already rooted, you can simply cut them from the parent and transplant, as you would a sucker. Any that have not yet formed roots only need contact with soil and time to set roots before becoming a full-fledged plant of their own. Leave the umbilical stolon attached to continue supplying nutrients while you give the plantlet or offshoot some loose soil to sit in, and keep it watered. After a week or two (or a month or two depending on the species and time of year) give the plantlet a little tug. If you meet resistance, roots have formed and you may cut the cord. Play it safe and transplant only after it has become visibly larger.
Layering
Some plants leapfrog through the garden, layering themselves in by forming adventitious roots wherever branch elbows or fingertips touch the soil. If a plant can manage such a feat, there’s no reason why gardeners shouldn’t take advantage of that energy and help them on their way. How do you know if a plant can be layered? Try it. Merely bending a branch downward sets a hormonal ball rolling inside that signals the plant to push out fresh vertical growth. If the versatile cells at the leaf nodes are placed in contact with soil, the plant will usually take the hint and grow roots there.
Plantlets dangle from a potted strawberry begonia (Saxifraga stolonifera).
Roots formed on this sweet-breath-of-spring (Lonicera fragrantissima) branch where it had been buried the previous season.
Wounding the stem to layer a Fothergilla gardenii, which otherwise spreads slowly by suckering.
Late summer into fall is the best time to propagate by layering because most plants will spend their energy on root production before they go into winter dormancy. By spring the rooted layers should be ready for transplanting. Start by digging a little hole and burying the branch tip in the soil. If a branch is really supple, bend it in arches and use a rock to pin the low points, each to include a leaf node, under the soil. Either way, a wounded stem is more likely to trigger root growth so let it crack slightly under the pressure of your pin (or, before burying the stem, nick the bark on the underside at a leaf node, where roots will form). Leave the branch attached so it can continue to draw energy from the rest of the plant until it makes its own roots. By the next spring or fall, after each bend or branch tip has made enough roots and leaves to support itself, you can sever the connection anywhere along the original branch, dig it out, and transplant it.
The wounded branch pinned under a rock to keep it in contact with the soil while roots form.
A flush cut at the top end of the root and an angled bottom cut helped me keep this root cutting correctly oriented for sticking.
When plants are dormant they store energy in their roots, which are often especially fat and full of carbohydrates in the winter. (Who isn’t?) By sticking root cuttings, we can take advantage of their urge to run around the block with that energy come spring. The best choices for this method are plants that aren’t easy to divide—such as oakleaf hydrangea, flowering raspberry, or any other large, established shrub—and anything from which you want more pieces than you would get via division. Young thick roots from healthy plants (of any age) will be most capable of sprouting. Start root cuttings during dormancy, after the plant’s leaves have fallen or died back to the ground.
Sticking root cuttings from shrubs
Expose some of the shrub’s roots before the ground freezes, or during a midwinter thaw, and select a few that are at least pencil-thick and fleshy rather than woody. (Don’t be greedy: never remove more than a third from a plant’s root system.) Because roots are hormonally oriented to produce new shoots from whichever severed end had been closest to the plant, maintain the roots’ polarity by making your first cuts straight across at right angles to the root so you’ll always know which end is up. Chop the root into smaller pieces (3 to 6 inches long) for easy planting and cut the bottom end on an angle to help remind you which end goes down. Make a fresh straight cut at the top of the next section, then an angled cut, and so forth down the root.
Replant the parent, water it in well, and apply a blanket of mulch to keep it from heaving out during winter’s cold snaps. Then “stick” the cuttings in a well-drained part of the garden by inserting the root sections vertically into the soil, pointy end down; the cuttings should be 1 or 2 inches below the soil level so that the flat top of the root is covered. If your soil is frozen, you can also root cuttings in containers placed on a cold porch or inside a cold frame. Either way, water the cuttings after sticking and continue to monitor them so they don’t dry out or sit in a puddle of water—rot is the most likely reason why root cuttings sometimes fail.
Sticking Tiger Eyes staghorn sumac root cuttings in potting soil.
Perrenial plumbago (Ceratostigma plumbaginoides) cuttings prepared for burial under ½ inch of soil. This cluster of roots produced a good-sized clump of sprouts; I transplanted the whole potful to the garden in early summer.
A plumbago successfully sprouted using the plastic bag method.
Depending on the species, new shoots may appear months later in spring. Other plants will form a full root system first and only send up shoots when they’re good and ready. Give your cuttings plenty of time to grow before moving them—or stick them where you wanted them in the first place. Make sure to label and date your cuttings to keep from planting something else in the same location.
Sticking root cuttings from perennials
Perennials, especially those with shallow root systems, are generally more forgiving about polarity, so it is less important to keep track of which end is up. Select roots that feel fat and healthy and cut them into 2- to 4-inch sections. Space them out horizontally in a container nearly full of dampened potting soil, cover them with another ½ inch, and water well. Place them on a chilly porch, in a cold frame, or by the window in a bright room. Cuttings taken over the winter or in early spring and kept cool should start sprouting as temperatures rise in spring. After most or all of them have sprouted shoots, pot them into individual pots to grow stronger before planting them outside.
TOOLS FOR PROPAGATING SPREADERS
• Spades are flatter than a shovel with rectangular or narrow blades that are easy to insert vertically in crowded beds. They usually have a D-shaped handle at hip height.
• Digging forks have four flattened sturdy tines (unlike pitchforks which have three to six thin pointy tines) and are squared off with a D-shaped handle like a spade. Buy two forks or borrow an extra one for dividing.
• Pruners (secateurs) and loppers are bypass-bladed tools for severing root connections precisely. They are also used to trim top growth and any stems that might get in the way.
• Hand saws are used to prune tree and shrub limbs above ground and to cut through dense mats of roots. Stony soil abuses saw blades so buy two, one for each task.
• Hori-horis (Japanese digging knives) and trowels are ideal for levering out small pieces of shallow-rooted plants. The hori-hori’s serrated edge is especially useful for sawing through fibrous roots.
A sturdy trowel and hori-hori (shown center, front) along with sharp pruners, loppers, and a saw (like the ones in the trug) are worth the investment to buy new, but look for secondhand spades and digging forks.
Another option is to partially fill a plastic grocery bag with dampened potting soil and root cuttings. Hang the bag in a bright place indoors, protected from freezing, check often for new growth and to remoisten the soil if necessary. Transfer cuttings to pots as soon as shoots appear.
A generously spreading hakonechloa and a potted bugle (Ajuga reptans ‘Burgundy Glow’) mingle in this shady border.
