Before propagating blueberries, evaluate land use in relation to time, land investment, equipment, labor, and structures needed. Identifying a source true-to-name and disease-free is essential for successful propagation. Do not propagate from plants adjacent to bushes showing disease symptoms.
A vast majority of blueberry propagation is done by relatively few commercial growers because of investment and cost. Most new growers can get into production sooner if they buy rooted cuttings rather than producing their own plants.
Highbush blueberries can be propagated by both hardwood and softwood cuttings. Most propagation is done with hardwood cuttings, as they are easier to handle and are less perishable than softwood cuttings. However, softwood cuttings allow more rapid multiplication of plants.
Cuttings are whips or shoots that are cut into several pieces, each 4 to 6 inches long. There are 3 types of cuttings: leaf buds only, 1 to 2 fruit buds in addition to at least 2 good leaf buds, and a cutting taken from the middle of the previous year’s growth with one or more fruit buds removed. Research shows a higher percentage of rooting is obtained from leaf bud cuttings than from fruit bud cuttings with fruit buds removed.
Selecting whip/cutting wood
Proper selection of shoots is important for rooting. Take dormant, well hardened, unbranched, one-year-old whips/shoots from “mother” plants. Whips should be one-fourth inch or less (pencil width) in diameter but not spindly. Do not use shoots formed late in the season, as they are poorly hardened; such shoots often have an off-white to brown pithy interior. Look for healthy leaf buds on the whip. Avoid wood that might be diseased with Botrytis twig blight, bacterial blight, or Godronia cane canker.
Cuttings made from wood greater than one-fourth inch in diameter don’t root as well, but may still produce desirable plants. Do not use thin wood unless cutting wood is scarce.
Prepare whips by removing the fruit buds and cutting the whips into lengths. Cuttings cut less than 4 inches long have a smaller stored food supply, so greater care is needed to get them to root.
Whips may be cut mechanically using a band or bench saw, or by hand using a sharp knife or pruning shears. Cutting by hand allows the basal cut to be nearer a vegetative bud; this is especially important for hard-to-root cultivars (table 1). The cuts must be clean, taking care not to damage or bruise the bark. To stimulate rooting, slice a one-half to one inch long layer of bark from both sides of the base of the cutting. Protect the cuttings from drying out.
Table 1. Rooting characteristics of hardwood cuttings of Pacific Northwest cultivars
Collect cuttings in early spring before bud break. Timing in Washington, Oregon, and Idaho is February/March for small-scale farms. For large-scale farms, start taking cuttings in late January. A minimum of 850 to 1,000 chilling hours is needed for shoot growth and flowering to occur (see Winter Acclimation and Cold Hardiness) . It is best to take cuttings in late March and place them immediately in propagation flats. However, often propagators must start early and store the cuttings.
Stored cuttings should be cleaned, placed in plastic bags with sphagnum moss, and stored at 34 to 40 F. Maintain a humidity of 80 to 90 percent. Temperatures below 30 F may damage the wood. Cuttings can be stored for 2 to 3 months. Ensure good ventilation when using boxes or trays. Fill boxes or trays with sphagnum moss to increase humidity and prevent cuttings from drying out. The shorter the length of storage, the better. Storage of cuttings can be difficult and should be done only if necessary.
Propagation beds should be located in full sun with a suitable well-drained medium. Place beds either on the ground or raised above the ground. Construct propagation frames from good quality, new, treated wood. The frame bottom should have crosspieces for supporting heavy-gauged wire. Place hardware cloth over the wire. Beds are usually 4 feet wide, 8 inches deep, and of various lengths. A well constructed propagation bed will help reduce insect, disease, mouse, and gopher problems.
Rooting frames should contain a heating source. Place frames in glass or plastic greenhouses. Recommended bottom heat is between 68 to 73 F. Often heating coils are used to maintain a more constant media temperature. Heat sources include propagation heating mats, hot water tubing, and lead, rubber, or poly-covered cable.
Good quality thermostats maintain a constant heat. See the manufacturer of these products for current recommendations and application methods. Avoid wide temperature fluctuations and drafts in the propagation bed and greenhouse structure to promote rapid and even rooting.
Rooting media include sphagnum moss, American, German, or Canadian peat, sawdust, sand, cinders, perlite, and vermiculite. Peat alone as a medium creates problems when trying to separate the roots before transplanting. Root media need to have a pH of 4.5 to 5.5. Fresh sawdust is not recommended.
Several medium mixes work well.
- Mix 1. 50% sphagnum peat moss and 50% coarse-washed concrete sand;
- Mix 2. 50% peat and 50% vermiculite or perlite;
- Mix 3. 30% perlite, 30% sand, and 30% vermiculite (or perlite).
Mix these media thoroughly before placing on the screens in propagating beds. Bluecrop requires a higher proportion of sand. Water the rooting medium thoroughly. Add extra medium as the new medium settles. Maintain a depth of 8 inches.
Before inserting the cuttings into the medium, label them well as to cultivar and mother block. Place the cuttings vertically (right side up with vegetative buds pointing upward) into the medium, leaving 1 or 2 buds above the medium (60 percent covered). If bottom heat is used, insert one-third to one-half of the cutting into the medium. The butts of the cuttings should not touch the bottoms of the frames. Set the cuttings in a 2- by 2-inch, or 2- by 3-inch spacing. For larger root development, a 3- by 3-inch spacing is recommended. Press the medium around the base of the cuttings. Failure to do so will cause the cuttings to dry out.
In the Pacific Northwest, cuttings are usually stuck, or inserted, from January 15 to March 10.
Water the cuttings thoroughly about once a week to keep the medium moist but not water-logged. Water more frequently when the leaves have developed. Full sun is best for growing quality plants.
During April and May, vegetative buds will produce leaves. By June, the roots begin to form. Fifty to 98 percent of the cuttings should root. The period of May 1 to June 15 is critical for root and foliage development.
After roots and foliage have developed, increase ventilation and apply fertilizer. Often fertilizer is applied weekly in a soluble form (i.e. 15-30-4, 13-36-13) or slow-release form. Nitrogen (N) is needed to maintain active growth. Nitrogen can be supplied as ammon-ium sulfate (1 oz/gallon water), am-monium phosphate, urea, or in other formulations.
When diseased cuttings or leaves are found, carefully remove and destroy them and increase ventilation, and/or apply appropriate fungicides (type depending on disease present).
Rooted cuttings remain in the medium to overwinter in the propagation frames. Remove rooted cuttings the following spring. Either line-out rooted cuttings in pots or place them in the ground, spaced 8 by 18 inches or 8 by 10 inches.
Softwood, or summer, cuttings are used to speed propagation of blueberry plants. Concord, Herbert, Ivanhoe, Stanley, and Bluecrop (which are difficult to propagate by hardwood cuttings) root more easily by softwood cuttings. However, softwood cuttings require a mist system and well ventilated propagating structures. Thus, blueberries are more difficult to propagate by softwood than hardwood cuttings.
Take softwood cuttings in June while the mother block plant is growing actively. Shoots of the first seasonal flush of growth make the best wood for cuttings. Take cuttings before fruit buds start to form.
Cuttings should be 5 to 9 inches long, with 2 or 3 leaves. Place cuttings 2 inches deep into rooting medium made up of equal parts of perlite and peat moss, or another acceptable mix.
Mist irrigation and shade are required to prevent foliage from drying out and dying. After roots and foliage appear, good air circulation will help prevent the spread of diseases. Periodic sprays of fungicides will serve as prophylactic measures to prevent Botrytis, root rot, bacterial canker, and other diseases. Check with your local county Extension agent to select and schedule use of proper fungicides to reduce likelihood of developing fungicide resistance.
Softwood cuttings should root in 4 to 7 weeks and can then be transplanted into peat or plastic pots. Plants can be forced in a greenhouse during the winter months for additional growth. A complete soluble fertilizer will help ensure good foliage and root growth. Do not allow evening temperatures to fall below 60 F.
Rooting hormones may increase the percentage of rooting of cuttings, but have not been proven effective.
A few laboratories have begun to propagate blueberries by tissue culture. This procedure allows for very rapid proliferation of certain cultivars, but also requires an expensive, specialized laboratory. The growing tips of plants are removed under sterile conditions and placed in a special growth medium in growth chambers. The resulting plantlets are carefully rooted under high humidity in a greenhouse and are generally sold in transplant trays.
Other Propagation Methods
The following methods of propagating are mainly used for research or propagation of only a few plants:
In this system, severely prune the mother plant, cutting back canes and young whips to 6 to 12 inches above the ground. Fertilize and then build a wood or tar paper frame around the plant and fill this with a rooting medium. After 3 years, remove the frame. One-sided root systems are produced near the base of the stems. After cutting below the roots, the plants are ready for transplanting. This method is rarely used.
Seeds can be used for propagation but are mainly used in breeding programs as plants do not breed true to type. The seeds need to be exposed to light to germinate, which takes 3 to 8 weeks. Seeds are sown on the surface of sphagnum peat or a 1:1 mix of sphagnum and sand. The medium must be kept moist.
Budding involves grafting a single bud onto another plant. Bud when the bark slips easily in the spring. Rubber grafting bands are good wrapping material to fasten the buds to the branch. Other types of grafts used are the cleft, whip, side, and T-bud.
Budding and grafting are not commonly used because blueberry plants are rejuvenated by suckers below the graft or bud unions. Within 4 to 6 years, these unions will be pruned out.
This fact sheet is adapted from Oregon State University Extension Publication PNW215, Highbush Blueberry Production. The authors of Highbush Blueberry Production are – Oregon State University: Bernadine Strik, Glenn Fisher, John Hart, Russ Ingham, Diane Kaufman, Ross Penhallegon, Jay Pscheidt and Ray William; Washington State University: Charles Brun, M. Ahmedullah, Art Antonelli, Leonard Askham, Peter Bristow, Dyvon Havens, Bill Scheer, and Carl Shanks; University of Idaho: Dan Barney. PNW215, Highbush Blueberry Production can be purchased from the Department of Extension & Experiment Station Communications, Oregon State University. How to Order