AMES, Iowa – Creating new plants from old ones, and forcing spring flowering trees and shrubs to bloom indoors is simple, according to horticulturists with Iowa State University Extension and Outreach. They share techniques suited for propagating grape vines and willow trees and forcing forsythia and pussywillow to bloom indoors. To have additional questions answered, contact the Iowa State University Hortline at firstname.lastname@example.org or 515-294-3108.
While grapevines can be propagated by several methods, they are most commonly propagated by hardwood cuttings. Hardwood cuttings are made from the dormant canes of the preceding year’s growth. Cutting material should be collected in late winter.
Home gardeners pruning their grapevines in late February or March can make cuttings from the pruned material. Grape cuttings should be approximately pencil-size in thickness and 12 inches long. When making the cuttings, the bottom cut should be just below the lowest bud, while the upper cut should be 1 to 2 inches above the top bud.
After making the cuttings, loosely tie them in a bundle. Place the cuttings in a plastic bag with some lightly moistened peat moss, then store in a cool location, such as a refrigerator or garage. As soon as the soil is workable in spring, remove the grape cuttings from cold storage. Set the cuttings in the ground vertically with only the top bud just above the soil surface.
Willows (Salix species) are easily propagated by hardwood cuttings. Collect cutting material on a mild day (temperatures should be above freezing) in late winter. Prune off branches that are about one-half inch in diameter. Bring the branches indoors and cut the branches into 12- to 18-inch sections. Bundle the 12- to 18-inch-long cuttings together with string or twine. Place the bundled cuttings in a plastic bag that contains some lightly moistened peat moss. Place the plastic bag in the refrigerator.
As soon as the ground is workable in spring, remove the cuttings from the refrigerator and stick the cuttings into the ground. Place the bottom 6 to 8 inches of the cuttings in the soil. Willow cuttings root easily. The cuttings should begin to root and leaf out within a few weeks. An alternate rooting method is to place the cuttings in a container of water indoors. Regularly change the water. When the cuttings have developed good root systems, remove them from the water and pot them up or plant directly outdoors.
Forcing can be done as soon as the buds start to swell in late winter. Forsythia and pussywillow can be forced as early as late February. It’s best to wait until March for more difficult-to-force ornamentals, such as crabapples, magnolias and redbuds.
Select branches containing round, plump buds. (Narrow, pointed buds are usually leaf buds. Flower buds are generally larger and have a more rounded shape.) Make clean, slanting cuts 1 to 2 feet from the tips of branches with a sharp hand shears. Selectively remove branches that won’t harm the appearance or shape of the plant. If pruning fruit trees in late winter, gather some of the pruned material for forcing indoors. If possible, collect branches when temperatures are above 32 degrees Fahrenheit. If the plant material is frozen when collected, submerge the branches in a tub or pail of water for a few hours.
Later, set the branches in a tall container of water and place in a dimly lit, cool (60 to 65 degree Fahrenheit) location. Spray or mist the branches two or three times a day to prevent the buds from drying out. Also change the water in the container daily during the forcing period. Daily changes of water should inhibit the growth of bacteria and fungi which could interfere with the absorption of water by the branches. When the flower buds begin to open, move the branches into a bright room. Keep the flowering branches out of direct sunlight and in a cool location to prolong the bloom period.
The time period required to force branches into bloom depends upon the plant species and collection date. Forsythia and pussywillow generally take only one to three weeks to force. Apple and crabapple branches may take two to four weeks. The forcing period for magnolias is three to five weeks. The closer it is to the plant’s normal outdoor flowering period, the less time it takes to force the cut branches indoors.