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Establishing High Yield Plantations
In most cases, high yield plantations will be established on cleared land. In western Washington and Oregon, consider agricultural lands not currently suited for cultivated crops. Usually, such lands are in grass for hay or pasture. Quality cropland also can be used, since methods are available to eliminate the stumps and return the field to agriculture. Special considerations required to establish plantations on grasslands are discussed below. For more details please refer to "High Yield Hybrid Poplar Plantations in the Pacific Northwest."
Genetic Diversity - Use of a single clone in plantations increases risk from insects and disease. Therefore, in extensive plantings (over 40 acres), plant several clones, either in pure blocks or in mixed clone stands.
Suitable soils - Hybrid poplars attain the best growth on deep, fertile, alluvial soils that have adequate moisture. One reason for their high productivity is their ability to fully use such soils. Light textured soils, such as sandy loams abd silt loams, are generally best, but heavier textured soils can produce excellent growth if the soil is relatively loose and friable.
Where can hybrid poplar be grown? - Use caution in planting hybrids developed for the Pacific Northwest in regions of the world that have unsuitable climates and significantly different latitudes. Even in similar climates, susceptibility to local diseases can limit hybrid growth.
Cold Injury - Most serious cold injury has resulted from sudden cold in fall. Low temperatures occurring later, when the trees are fully dormant, is of little concern. Spring frosts can injure newly emerging leaves and succulent stems. Such damage occurs both east and west of the Cascades in Washington, but rarely kills trees. The other type of cold injury noted with older specimens of certain clones is frost cracking of the trunk.
Choosing the spacing - If trees will be harvested as biomass fuel, small sized trees as young as one year can be used. Expect resrouting for subsequent harvests (provided harvesting is done in the dormant season). Under such conditions, use close spacing - 2 x 4 feet or 4 x 4 feet. Spacing for longer cycle cuttings can range up to 20 x 20 feet, depending on the size of the tree desired.
Land Preparation - Proper land preparation is vital for ensuring high productivity plantations. The major objectives in land preparation include:
1. controlling competing vegetation
2. loosening the soil by plowing, ripping, subsoiling, and
3. improving drainage by using either surface ditches or subsurface tile.
Cost share assistance - Establishment of hybrid poplar plantations may be eligible for USDA cost-sharing funds if harvest rotations exceed 10 years. Local offices of the USDA Agricultural Stabilization and Conservation Service (ASCS) or your state forestry agency, Washington State Department of Natural Resources, Oregon Department of Forestry, or Idaho Department of Lands can advise you regarding the eligibility of hybrid poplar in your area.
Time of planting - The best time for planting west of the Cascades is January to April. Establish plantations east of the Cascades from March 1 to April 15. Early planting improves tree establishment and aids chemical weed control.
Obtaining planting material - Hybrid poplar cuttings are available in the United States from many sources. However, it is important to use only clones proven to be adapted to the area where they will be planted. Cuttings of the UW/WSU hybrids are available from several sources.
Age of cuttings - Cuttings are made from dormant 1 year of shoots, although plants can establish successfully from older shoots and branches. Growers harvest 1 year-old shoots from plants (stools) grown and maintained for production of cutting material. Most commonly, cuttings are 12 inches long, but can range from 6 to 24 inches. The minimum diameter for stem cuttings is about 3/8 inch.
Storing cuttings - If you cannot plant dormant cuttings shortly after they have been prepared, protect them from drying by enclosing them in plastic bags and refrigerating at temperatures ranging from 10 - 28 F. Temporary planting (heeling in) in soil or potting mix for later transplanting is not recemmended, since roots will form quickly and are are easily broken when the cutting is transplanted.
Soaking cuttings - Encourage root formation on late planted (after mid-March) cuttings by submerging the lower fourth of the cuttings in cold water for 2 to 4 days prior to planting.
Planting the cuttings - Plant cuttings vertically and right side up. Soft, wet soild conditions during winter (January-March) in the wetter areas of the Pacific Northwest generally require hand planting. Plant cuttings deeply in cultivated ground leaving 1 inch or less above ground. Firm up soil around the cutting to ensure good contact.
Resprouting after harvest - when using shorter harvest cycles (up to 4 to 5 years), multiple harvests are possible before replanting is needed. Dormant season harvest ensures maximum sprout vigor. Problems associated with resprouting in plantations occur when harvest cycles exceed 4 to 5 years. These include:
1. sprouting is less reliable
2. sprout attachments are weaker, making the trees less resistant to wind; and
3. stumps and, consequently sprouts are more likely to become infected with wood decaying organisms.