Four options exist for starting perennial plants. They are:
- direct seeding,
- indoor production of transplants from seed,
- purchasing and transplanting, and
- obtaining starts from existing plants.
Though the majority of perennials are vegetatively propagated to preserve trueness-to-type, some perennial plants may be grown from seed. Planting seed is the simplest and cheapest propagation method. The advantages of direct seeding are offset by the tendency for plants to be slow and erratic with respect to emergence and early growth. These are usually a problem only in the first year, during which they may delay flowering and shorten the color display of the bloom period.
Plant seed in shallow trenches and cover lightly. Plant extra seed and thin after emergence, if necessary. Refer to the seed package to determine seeding rate. Maintain good moisture at the soil surface by misting lightly until the plants emerge. Once plants are established, deeper irrigation should be applied only after the top 1-2 in. of the soil surface dries out.
Indoor Seeding and Transplanting
Growing your own transplants has the best features of both direct seeding and purchase of transplants. However, it has the same limitations of availability as direct seeding. The key to success is providing appropriate conditions for germination and early growth of the new seedlings. Soil, temperature, light, and moisture are the most important elements. The soil medium must be free of disease organisms that may cause death of germinating plants. The best soil medium is a commercial potting soil. Containers may range from recycled plastic pots, paper cups, or commercial seed plug trays. Wash and disinfect all containers before using. Temperatures should be warm enough to allow germination (e.g. 60-75 F during the day and slightly cooler at night).
Unless a greenhouse is available, artificial lighting will be required. Even a south facing window does not supply young plants with enough light to keep them from getting ‘leggy’ and weak. Some seedlings may need as much as 18 hours of light each day to remain healthy. Fancy equipment and expensive “grow lights” are not necessary. A standard fluorescent shop light, easily found at home improvement and hardware stores, fitted with one “warm,” and one “cool” tube works very well. Suspend the light fixture 12-18 inches from the plants and raise as growth occurs. It is also important to keep water availability balanced between too wet and too dry. This requires frequent, light irrigations.
Before transplanting, seedlings should be hardened off. This refers to the procedure of adapting the plants to outdoor conditions to reduce transplant shock. This can be done by placing the plants outdoors in full sun for increasing amounts of time each day for the last week or ten days before planting. Hardening the plants will improve survival and increase the early growth rate. The process of transplanting self-produced plants is identical to that described below for purchased plants.
Buying established plants is the most common method of obtaining perennial plants. It is also the most expensive, but transplants will result in quicker establishment and a longer flowering period during the first year.
When choosing transplants, it is best to buy from a nursery or garden store with personnel knowledgeable about local growing conditions. This will assure availability of adapted species and varieties. Do not look for the largest plants, or necessarily, those that are in bloom. You want the perennial to spend it’s bloom period in your garden, not in the nursery! Seek plants with good dark green color, healthy root systems, and no sign of disease or pest problems. Try to find plants that have been hardened off, in order to aid the transition to the yard.
For most perennial plants, timing of transplanting should correspond with a date one week later than the last frost in your region. Even though some perennial seedlings will withstand relatively hard frosts, there is little advantage to early planting given the longevity of these plants. To estimate the last frost date in your area, look at the Idaho chart compiled by Ed Hume Seeds.
It is best to transplant on a cool, cloudy day with little wind. This will allow acclimation under conditions of limited water loss. After removing a plant from its container, tease roots away from the surface of the root ball. Don’t plant the seedlings too deep. Bury the root ball in a hole sufficiently deep only to bring the soil slightly above the pot soil level. Space the plants according to the instruction on the seed packet or nursery pot label. For the first 7-10 days, water the plants frequently and lightly. For the first few days, the root ball holds all of the roots and is the only source of water. The root ball will need to be wetted as often as it would in the pot until the roots can become established in the surrounding soil.
Depending on the species, vegetative propagation of perennials is probably the most common method commercial growers use for starting new plants. Homeowners can take advantage of propagation techniques to obtain starts of flowers already in place in their own yard and other places. This requires permission from the owner and a little extra work, but may require no purchase.
A few precautions are needed before trying to propagate a perennial plant. First, it is important to inspect the source plant to make sure it is healthy and free of visible disease. Then it is important to obtain adequate knowledge of the best methods and procedures for propagation of the species of interest, including the proper time of year. Here is a description of the most commonly used propagation methods:
Division – Many perennial plants develop a large multiple crown as they age. These can be cut into two or more pieces to create new plants. This can be done by digging up the plant, dividing into pieces, then replanting each one, or by using a sharp spade to cut a portion from a plant left in place, then replanting the removed segment. This latter method minimizes disturbance of the original plant. Perennials commonly divided include Shasta daisies, phlox, daylilies, iris and chrysanthemums.
Stem Cuttings – Some perennials easily grow roots on stems cut from growing plants, allowing the production of new plants. This method is commonly used by nurseries in lieu of planting seed. Stem cutting is usually done indoors and involves removing a stem tip or middle piece of a healthy, green shoot and poking it into sterile, moist growing medium. The new cutting should be kept out of direct sun and covered with clear plastic (plastic cups work well if only a few cuttings are being rooted) to prevent moisture loss. It usually takes 2-3 weeks for cuttings to develop new roots and several more weeks to be ready to transplant. Many soft-stemmed perennials can be successfully stem cut.
Root Cuttings – Perennials with thick, fleshy roots can be propagated by removing a portion of root and replanting in a new location. It is done by simply digging up a portion of root, cutting it into segments, and replanting each piece. Usually, the larger the root cutting the faster a new plant grows and blooms. Root cuttings, as a rule, should be taken when plants are dormant. Perennials that usually respond well to root cutting include peony, baby’s breath, and bleeding heart.
Layering – Some perennials that vine or have long, flexible stems can be layered, This involves bending a stem to lay along the ground, then covering a middle portion with moist soil (use a pot if the plant will be moved a long distance), leaving the tip uncovered. The covered part of the stem will grow roots, after which the stem can be severed from the original, thus creating a new plant. The rooting process may be helped by scratching or gouging the stem on or below the portion that will be covered. Perennial vines can usually be successfully layered.
In his web site, Dr. Leonard Perry, University of Vermont, provides information on the best method for propagating individual perennial species.