Propagation

The expense of purchasing trees and shrubs can be avoided by propagation of existing plants. Growing your own trees might also be considered when availability of particular species are limited or difficult to obtain. Propagating plants using cuttings can also guarantee that the offspring will be identical to the parent. This may be an attractive option when a plant exhibits particularly desirable characteristics. Growing plants is for many people a satisfying and interesting challenge.

The methods used for propagating trees and shrubs:

Growing trees and shrubs from seed

Growing tree and shrub seedlings at home is similar to growing garden plants for transplanting as the seedlings are delicate and require careful attention. Growth is slow but with proper care the seedlings will attain sufficient size within a few years to enhance your property or be ready for sale.

Obtaining Seed

The first step in seedling production is to obtain good quality seed. It is essential that seed, either purchased or collected, be from locations similar in climate and latitude to the one in which the plants will eventually grow.

When collecting your own seed try to collect the seed from plants with superior traits such as disease resistance, hardiness and form. Collect the seed when it is ripe (see attached table) and label the seed with the name of the species, source of seed and date of collection.

Tree and shrub seeds have specific processing requirements depending on seed type. Coniferous cones are picked before dispersal and spread in a thin layer in a well ventilated, warm room until the scales open. The cones are then gathered together and shaken to release the seed.

Fleshy fruits such as chokecherry and saskatoon are handpicked or shaken from the tree or shrub. The seeds are extracted by mashing the fruit to a pulp and then separating the seeds from the pulp by flotation. Small quantities of fruit can be macerated in a blender. The sound seed will settle to the bottom of the blender and the water and pulp can be poured out.

Dry fruit, such as caragana or lilac, can be spread thinly on a bench in a warm, ventilated room. The fruit will split open releasing the seeds which can be separated from the debris by shaking through a mesh screen.

Seed Germination

When tree and shrub seed does not readily germinate following ripening, it is said to be dormant. Dormancy is a protective mechanism that prevents newly germinated seed from being destroyed by the cold of winter. In nature dormancy is overcome by changes in temperature and moisture or by passing through digestive systems of birds or animals. The degree and type of dormancy varies with the species.

Mature seed of elm, poplar, caragana and Scots pine exhibit little dormancy and germinate readily, whereas, ash, chokecherry, maple and White spruce have an embryo dormancy and require a cold period or stratification to ensure germination. The attached table outlines stratification requirements of common trees and shrubs grown in the prairies.

Dormancy of many species can be overcome by sowing in the fall immediately following seed collection. Fall sowing takes advantage of cold winter temperatures which satisfy stratification requirements. The seed will germinate the following spring as temperatures increase.

When it is desirable to sow seed outside in the spring or inside in pots, the seed of hard to germinate species must be stratified in a medium such as moist sand at 5.0  Celcius (C) for various length of time depending on the species. The media used for stratification should be sterilized in an oven at 80 C for a few hours to prevent buildup of mold.

The sand is then cooled and water is added at 10 per cent of the dry weight. The volume of sand should be five times that of the seed. The moist sand and seed is mixed, placed in a sealed container and stored at 5.0 C (a household refrigerator is adequate) for a specified period (see Table).

The seed should be checked frequently during the stratification period to determine if the sand is too dry, the seeds are sprouting, or mold is developing.

Preparing the Seedbed

Proper seedbed preparation is essential for successful establishment of seedlings. The seedbed should be in a well drained location with a sandy-loam soil. To facilitate drainage, beds are often raised by furrowing or erecting side boards. Conifers require shading in their first growing season which can be provided by erecting side boards and covering with snowfence.

Deciduous trees and shrubs generally do not require shading. The size of the bed will vary but generally a 1.0 metres (m) × 3.0 m bed will be adequate for approximately 1,500 seedlings.

Sowing

Conifer seed can either be broadcast or sown in rows. Rows are easier to maintain. If sowing by hand, shallow trenches 2.0 centimetres (cm) wide and 15 cm apart are made. The seed is sown at approximately 150 seeds per metre and covered to a depth two to three times the diameter of the seed with fine sand or soil.

After sowing, shading is required and the seedbed should be kept moist until germination occurs. Seedlings are usually left in the seedbed for two years before being transplanted to a larger area.

Deciduous seed can be sown in rows or broadcast. Seeds are generally sown at a rate of 90 seeds per metre and to a depth approximately three times the seed diameter. Irrigation stimulates germination and hastens growth. The seedlings usually reach sufficient size for planting in a permanent location in two years.

Growing trees and shrubs from seed
Stratification Sowing Date for+
SpeciesSeed CollectionSpring SowingNon-Stratified Seed
* Species listed as "difficult" require long stratification at various temperatures or acid soaking.
+ Stratification temperature 5º C.
Coniferous
Colorado spruce Mid-September Not required May
White spruce September 90 days September
Scots pine September Not required May
Siberian larch Early to mid-September 90 days September
Deciduous
American elm Early to mid-June Not required June
Amur maple Mid-September Difficult* September
Asian rose Late September 120 days September
Buffaloberry Late September 90 days September
Bur oak Early September Not required September
Caragana August Not required May
Chokecherry Late August, early Sept. 90 days September
Cotoneaster September Difficult When seed is ripe
Cranberry Mid-September Difficult August
Dogwood July to September 60 days October
Green ash Late September 90 days September
Honeysuckle Late July 30 days October
Hawthorn September Difficult August
Manitoba maple Mid-September 90 days September
Mayday Late July 90 days September
Nanking cherry Late July to early Aug. 90 days September
Nannyberry Late September Difficult August
Native plum August to early Sept. Difficult September
Paper birch September 60 days October
Pincherry Late July to early Aug. Difficult August
Red elder Late July 90 days September
Russian olive Early October 30 days October
Saskatoon July 120 days September
Sea buckthorn Early September 30 days October
Siberian crabapple Late September 30 days September
Siberian elm Early to mid-June Not required June
Snowberry Late Sept. to early Oct. Difficult August
Villosa lilac Late September 30 days October
Wolfwillow Late September

Propagation by Softwood Cuttings

Many species of trees and shrubs can be propagated from softwood cuttings taken in June or July or as soon as there is sufficient new growth (about 13 cm). The new shoot is cut off about 2.5 cm below the new wood and placed in a container of water until it is ready for planting.

The cutting can be rooted indoors or outdoors. Prepare a flat or tray about 13 cm deep and small enough to handle easily. Fill the flat with fine screened sand or vermiculate. Level the media to 1.25 cm below the edge of the container, then water to saturate the entire flat.

Take the shoots from the water, remove the leaves from the lower 7.5 cm and cut off the old wood. The cut is made diagonally so that there is a tip of old wood attached to the new wood. The cutting is planted at a slight angle and as deep as possible so that the leaves are even with the sand surface. Pack the sand firmly and water. Keep the sand moist, but not wet, until rooting occurs, usually in about three to four weeks.

A rooting hormone is beneficial for some species. The base of the cutting is dipped into the powder and the excess is removed by gently tapping the cutting. The cutting is then planted.

The leaves must be kept fresh until rooting occurs. This is achieved by constructing a tent of polyethylene over each flat supported on stakes about 30 cm long. The edges can be stapled to the side of the flat. Place the flat in a shady area. The optimum conditions for rooting are about 70 per cent relative humidity at 21° Celsius (C) temperature.

When the plants have rooted, they are lifted out of the sand and planted into good garden soil either in pots or directly into the garden. Some shade is beneficial and continued watering is essential. In the fall the plants should be covered with leaves, straw or any material which will prevent freezing.

In the spring the plants are uncovered. They can then be planted to a permanent location or grown for another year to get a larger plant.

Plants which are rooted in a sand soil mixture can be left in the flat until the following spring. When rooting is complete, the polyethylene cover can be removed. The plants should be protected over winter as described above.

Growing Poplar and Willow from Hardwood Cuttings

Collection

Poplar and willow cuttings should be collected from healthy trees while they are dormant in the late winter or early spring before the buds break. Cuttings should be taken from the ends of the branches (previous summers' growth) and could be anywhere from 7.5 cm to 1.0 metre long depending on the tree it was collected from and the conditions for growth that year.

Cuttings should be made approximately 15 cm to 25 cm long and should include at least four or five buds. If the cuttings are taken in early winter, they must be stored in sealed plastic bags and placed in a snowbank on the north side of a building until they are planted in the spring. Another method is to store them in a cooler, at below freezing temperatures.

The best method is to leave them on the tree until a week or so before they break bud; place them in a sealed plastic bag and keep them in the refrigerator at 5.0 °C until the ground thaws and the cuttings can be planted.

Pre-planting Preparation

The area for planting should be very loose and worked deep so that the cuttings can be pushed into the soil vertically to their full depth. A well-worked garden plot is best. The cuttings seem to take root much quicker if they are soaked in water for three days prior to planting to the soil.

Do not leave them in water for more than three days or small roots will form on the cuttings which will be ripped off when the cutting is pushed into the soil.

When soaking the cuttings, be sure the cuttings are fully immersed in the water and are not floating on top. The best way to do this is to wrap a bundle of them with an elastic band and put a weight on top of the bundle.

Planting

The cuttings can now be planted into the garden plot. They should be pushed in straight up and down by hand so that the whole cutting is below ground and the top is just flush with the soil level.

Be sure to plant the cuttings with the buds facing upward. Plant the cuttings about 30 cm apart so that they can be dug up and moved to a permanent location at a later date. They can be planted to their permanent location right away, but it is usually easier to look after them for the first year in a garden plot where they can be watered and kept free of weeds.

Once the cuttings have been pushed into the soil, pack the soil firmly around the cuttings and water them immediately. They will need water whenever the soil gets dry, but do not overwater them. A water-logged soil has no aeration and the cuttings could die.

Note: Do not plant cuttings into trifluralin treated soil.

Transplanting

The cuttings will form a great deal of roots in one year under ideal conditions and so if they have been planted temporarily in a garden plot, they must be moved after one growing season or it will be difficult to move without damaging a lot of the roots.

Plan to transplant the rooted cuttings to their new location in the early spring before the seedling starts to grow.

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