Finish Transplanting Before Winter Ends

90220thumbAutumn is for planting; and for good reasons. It is the beginning of dormancy for almost all plants, including evergreens. It precedes cool and rainy weather that inhibits desiccation until new roots are able to disperse sufficiently to sustain new plants. Some plants need to be in the garden in time for winter chill in order to initiate bloom. However, not everything should get planted in autumn.

Winter is the best season for some plants. Many summer blooming bulbs get planted in winter because they are likely to start growing prematurely and get damaged by frost if planted in autumn with spring bulbs. Some perennials that are slightly sensitive to frost may get planted after average frost season so that they can bulk up enough to be more resilient to frost by the following winter.

Besides new plants that are purchased from nurseries to be planted in the garden, there are plants that are already established in the garden that might need to get dug, divided, and then planted back into the garden, or shared with friends and neighbors. Some might need to be transplanted because they are crowded or in the way of something. These present a different set of variables.

Once divided and transplanted, grasses, New Zealand flax, lily-of-the-Nile, African iris and other stoloniferous perennials (that spread by creeping stems known as stolons) are more susceptible to rot than nursery grown plants, because so many of their roots get severed. Even if aggressively pruned while getting divided and transplanted, shrubby plants, like lilac and forsythia, are more susceptible to desiccation than nursery grown plants, simply because they lack sufficient roots.

If divided or transplanted through winter rather than autumn, plants get a few weeks of cool and rainy weather to settle and disperse their roots, but do not have enough time to rot or desiccate before the weather gets warm enough for them to resume growth and recover resiliency. Perennials that get cut back in the process spend less time looking shabby before new growth develops.


Propagation Of Perennials By Division

80718thumbAutumn is for more than planting. It is when most of the aggressive pruning gets stared. It might be the best time to work with compost and conditioning the soil. Bulbs get planted. Gutters get cleaned. Leaves get raked. Perennials get groomed. We might think of it as a time of slowing down after such a busy summer, but in many gardens, autumn is just as busy with seasonal chores.

Autumn is when many of the spring, and some of the early summer, blooming perennials get divided. That means that they get dug up, split into smaller parts, and then replanted. Because there will be more smaller plants after the process than there were bigger plants before the process, some should get planted over a larger area, in other parts of the landscape, or shared with friends.

Not all perennials need to be divided annually, and some may never need to be divided at all. Perennials that bloom in autumn or winter, such as Japanese anemone and bergenia, get divided in spring, since they will have plenty of time to recover from the process to bloom on schedule. Black-eyed Susan does not likely care if it gets crowded, but can get divided simply for propagation.

Lily-of-the-Nile should be divided if it gets too crowded to bloom well. Division allows more room for the individual shoots to grow and bloom as they should. However, because it takes a while for newly divided shoots to recover, they should only be divided every few years or so, and only if they happen to be getting crowded. African iris gets divided if overgrown plants are looking shabby.

It is not always necessary to dig entire plants. If dividing New Zealand flax just for propagation, it is easier to pry the desired number of side shoots from a mature clump, without digging the main part of the clump. Agave pups might be (very carefully) pried off of larger rosettes just to keep the main rosettes neat. Black-eyed Susan and other deciduous perennials get divided while bare.

Division Is Equal To Multiplication

70809thumbMathematically, division is the opposite of multiplication. Horticulturally, they are the same. Digging and splitting overgrown perennials to propagate them is known as ‘division’ because it divides many rooted stems or rhizomes of one plant into many new plants. Division is a form of propagation; and propagation is commonly known as multiplication. So, we divide plants to multiply them.

Autumn is generally the best time for panting. It is after most of the warmest and driest weather, and just before the cool and rainy weather that keeps newly planted plants from getting too dry. It seems obvious that autumn would also be the best time for division. However, a few perennials that are dormant or mostly dormant by the middle of summer can be divided now for an early start.

Bearded iris may not look dormant with their leaves still green, but they are about as dormant now as they will get. If divided now and allowed to slowly disperse roots through the remainder of summer, they can prioritize the production of new foliage when they come out of dormancy in autumn, like they would do naturally. Like many perennials in mild climates, they grow through winter.

Once dug, the plump rhizomes need to be separated from the old shriveled rhizomes that they grew from. For most, the best segments of rhizome are between the leafy tips and the stalks of the flowers that bloomed earlier this year, although it may not be easy to see where floral stalks were attached. The older sections of rhizome behind the flower stems are probably shriveled already.

The freshly divided segments of rhizome should then be groomed of deteriorating old leaves. Remaining green leaves can be cut in half to remove drying tips. Rhizomes then get replanted just below the surface, with the perpendicular fans of foliage standing upright. The main difficulty with dividing iris now is that they will need to be watered until the rain starts late in autumn. Bergenia, lily-of-the-Nile and a variety of perennials with big rhizomes get divided in a similar manner.


80509Wow, this is quite old school. Is it making a comeback? That would be nice. Avens, which is also known as Chilean avens, Geum quellyon, is an old fashioned perennial relative of the strawberry. Instead of producing fruit, it provides handsome yellow, red or coppery orange flowers that look something like small single, semi-double or double anemones, but can bloom through most of May.

Although perennial, avens do not last forever without some degree of help. After the first season, most of the slightly ruffled and hairy foliage dies down during the colder part of winter. New foliage and bloom develop in spring. After the second or third year, and every few years afterward, mature plants should be divided before or after bloom. Pups are more vigorous than the parent plants.

Happy avens gets as high and wide as a foot and a half. Much of the height is in the branched floral stems, which might need to be staked if they get too heavy with bloom, or are in a breezy spot. Most of the mounding foliage is basal. A bit of shade is tolerable and actually preferred to hot situations. Soil should be rich and well drained. Avens plays well with others in mixed perennial beds.

Perennials Can Divide And Conquer

10810Along with all the bare root fruit trees, roses and cane berries, nurseries also stock bare root perennials like strawberries, asparagus, horseradish and rhubarb. They are so easy to plant while dormant. They recover from transplant through spring, and by summer, should be growing as if they had always been there. Although, if they had always been there, they might be crowded by now.

Yes, many but not all perennials eventually get crowded. Strawberries spread by runners, so are easily plucked and transplanted to avoid overcrowding, as well as to propagate more productive plants. Asparagus are variable, so may not get crowded for decades. Horseradish and rhubarb may not mind getting crowded, but could be more productive if individual plants have their space.

For example, crowded horseradish plants produce many small roots. If dug, split apart, and replanted with more space between individual plants, the individual roots get much larger. Separating the roots, which is known as ‘division’, also produces many more new plants. Mature rhubarb plants may not mind being crowded, but are often divided simply to propagate new productive plants.

Division of these sorts of perennials is typically done while they are dormant through winter. If that sounds familiar, it because it is the same reason why these sorts of perennials are available as bare root stock. They get processed while they are unaware of what is happening, and wake up in their new and better situations. Many defoliate while dormant. However, most are evergreen.

Ornamental perennials like lily-of-the-Nile, African iris, New Zealand flax, society garlic, torch lily, lily turf and acorus grass are all good candidates for division if and when they become overgrown. So are most aloes, some terrestrial yuccas, several ferns and some of the more resilient clumping grasses. Agave pups can be dangerous, but really should not be allowed to get too crowded.

Division might be as simple as taking a few pups or sideshoots from a large clumping plant, or as involved as digging an entire large plant to divide each individual shoot. More often, large plants get dug and split into a few smaller clumps of many shoots. New plants should be groomed of deteriorating foliage. The long leaves of New Zealand flax should be cut in half to avoid desiccation.