Propagation by stem cuttings is the most commonly used method to propagate many woody ornamental plants. Stem cuttings of many favorite shrubs are quite easy to root. Typically, stem cuttings of tree species are more difficult to root. However, cuttings from trees such as crape myrtles, some elms, and birches can be rooted.
A greenhouse is not necessary for successful propagation by stem cuttings; however, maintaining high humidity around the cutting is critical. If rooting only a few cuttings, you can use a flower pot .Maintain high humidity by covering the pot with a bottomless milk jug or by placing the pot into a clear plastic bag. Cuttings can also be placed in plastic trays covered with clear plastic stretched over a wire frame. Trays must have holes in the bottoms for drainage. The plastic will help keep the humidity high and reduce water loss from the cuttings.
There are factors the affect this procedure:
Time of year cuttings are taken may affect rooting considerably. Expect best results from cuttings of many deciduous plants taken from late fall to early winter before enough cold weather occurs to complete the rest requirements of the leaf buds. This allows the cutting to be rooted under warm conditions without development of leaves. After rooting has started, however, the cuttings must be subjected to cold temperatures according to individual plant requirements. Some deciduous plants only can be rooted from leafy softwood or semi-hardwood cuttings taken during the growing season. Others root readily almost any time of the year.
Age of stock plant may be an important factor with hard-to-root plants. Cuttings from young seedling plants may root better than cuttings from older plants. Chances of rooting cuttings from large, old trees or shrubs may not be very good unless they are easy-to-root types.
Physical condition of the stock will affect the rooting of cuttings. Cuttings taken during the growing season from rapidly growing, succulent shoots often root poorly. Instead, take cuttings after growth has stopped and the wood has begun to harden; otherwise, many may rot. Shoots that have grown very little also root poorly. Neither type of shoot has the optimum physical condition and nutritional balance for the best rooting.
Wounding the basal end of the cutting often stimulates rooting of such evergreen plants as rhododendrons and junipers, especially if the cutting has older wood at its base. Use the tip of a sharp knife to make a 1- to 2-inch vertical cut down each side of the base of the cutting. Stripping off the lower side branches of the cutting during its preparation also can be considered slight wounding. For more severe wounding on difficult-to-root types or larger-diameter cuttings, make several vertical cuts. Or remove a thin slice of bark down one or both sides of the base of the cutting. Expose the cambium (the one or two layers of cells between the bark and the wood), but avoid cutting deeply into the wood.
Temperature must be controlled for optimum rooting. A desirable temperature encourages root formation but does not cause excessive moisture loss. Most leafy cuttings do best with air temperatures of about 60° to 65°F. Additional heat, 5 to 10 degrees higher than the air temperature and applied to the rooting medium, encourages rooting. Heating coils often are used beneath the rooting medium in the propagating bench to provide this effect.
Plant species may influence rooting. Many deciduous and evergreen plants are propagated from hardwood cuttings, but they vary considerably in ease of rooting. Honeysuckle, currant, grape, and willow root readily. Apple and pear are more difficult, while cherry and lilac are usually very difficult to root using hardwood cuttings.