Propagation of Perennials OH 28
Leonard Perry, Extension Professor
Perennial flowering plants are often favorites in the garden. Once at home in a garden, most perennials grow and spread--some rapidly, others more slowly. Plants that grow too slowly or too fast may require artificial means of propagation to keep them healthy and vigorous.
The simplest method of spreading and increasing plants is to divide clumps after several years. The digging, dividing, and replanting should be done at times that best suit the plants, not the gardener.
The general rule is that spring-flowering perennials are taken up in very late summer or early fall. Sections of clumps are reset at once and make good rooting before the onset of cold weather. With a thin straw mulch, the following come through the winter in good condition:
|Aubrietia||Bishops goutweed||Brunnera (anchusa)|
For the following summer- and fall-flowering perennials, dig in early spring before new top growth is more than two or three inches high:
|Achillea (yarrow)||Ajuga||Anemone, Japanese|
|Lobelia||Mallow||Monarda (bee balm)|
Dividing soon after flowering is advised for the following:
The mid-summer dormant period is the only time for oriental poppy.
If clumps will not pull apart easily, use a sharp knife; dense clumps may require splitting with a sharp spade. Always discard the older, central section. Be fairly generous with sections to be replanted; five or six new shoots will give good display. Always replenish soil with well-mixed compost and manure.
New plants from cuttings: Prepare a simple, flat cutting box, with wire wickets, and a tent of clear plastic. Fill the box with equal parts by volume of sterilized and moist, sharp, coarse sand and peat. Make 4-inch cuttings of tip growth as soon as plants are large enough (early in the season). Dip the bases in rooting hormone and set 1-inch deep in the sand-peat mix. Cover and place the box in filtered shade. One last sprinkling with water is advised, then secure the cover underneath the box bottom. Some plants will be ready in 3 weeks; test a few from time to time, and open the cover for several days before removal to harden off the plantlets. Try rooting these from cuttings:
|Coreopsis||Dianthus (pinks)*||Dicentra (bleeding heart)|
Plants from layers: Many creeping plants--rock-garden types--can be increased by layering, a process more useful for certain shrubs. Cover a short section of branch with moist soil and hold it down with a stone. If the soil is kept moist, the rooted branch can be cut loose by the end of summer and replanted. Aubrietias and dianthus (pinks) respond well to such treatment.
Seeds only. For many choice perennials, the only means of reproduction is by seed. They may have tap roots which do not permit division (gypsophila, baptisia, globe thistle), nor even moving after a year or two. Our favorite biennials are seed grown. Pansy is usually from seed, though if a particularly fine variety is found, it may be continued by cuttings. The finest delphiniums come only from fresh seed a few weeks from the pod; professionals use basal cuttings, rooted in a greenhouse. False indigo and lupine are best seeded where they are to grow, as they reject moving. Starting them in peat pots or cold frames makes this rule a bit more flexible. Grown from seeds are the following:
|Asclepias (butterfly plant)||Columbine||Delphinium|
|Dictamnus (gas plant)||Digitalis (foxglove)||Helenium|
|Platycodon (balloon flower)||Veronicas|
For late-summer seedings, a cold frame is a necessity. Small plantlets are better protected for the winter and from heaving out of the soil in early spring. An old storm window makes a good cover.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. Lawrence Forcier, Director, UVM Extension System, Burlington, Vermont. University of Vermont Extension System and U.S. Department of Agriculture cooperating, offer education and employment to everyone, without regard to race, color, national origin, sex, religion, age, disability, political beliefs, and marital or familial status.
Last reviewed 2003