Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
11/6/00
Yard and Garden Column for the Week Beginning Nov. 10
Contacts:
Paul Wray, Forestry Extension, (515) 294-1168, phw@iastate.edu
Elaine Edwards, Extension Communication Systems, (515)
294-5168, eedwards@iastate.edu
Planting Tree Seeds
By Paul Wray
Extension Forester
Iowa State University Extension
Each fall as our forest and urban trees unload their seeds and fruits, one question is asked. "Can trees be grown from seeds?" The short answer is yes but the long answer is a little more involved.
Here are some considerations when planting trees from seed. Collect seed when it is mature. A good indicator of maturity is when the seed is naturally falling from the trees. Most trees mature in the fall. A few trees (elms, silver maple, red maple, cotton and willows) produce seed in the spring or early summer.
Most tree seed is not mature and will not immediately germinate when it falls from the tree. This characteristic helps protect the species. If the seed germinated after falling in the fall, the tree seedlings would not be hardened off sufficiently to withstand an Iowa winter. To finish maturing, tree seed must be exposed to a period of moist cold. This stratification process may be accomplished most readily by fall planting. With some species, storage of the seed in a moist media such as sand or peat moss in the refrigerator will complete the maturation process and get the seed ready for spring planting. The white oaks (white, bur, swamp white, chinkapin and post) must be planted soon after collection in the fall because they germinate and send out the root system in the fall. Spring and summer maturing seeds are ready to germinate immediately after falling and should be planted as soon as collected.
Many tree seeds are quite perishable and only viable for a short period of time. Excessive drying is detrimental to many seeds. For example, buckeyes or horsechestnuts may have a viable life of only a couple of days after falling before they will not germinate. Oaks remain viable for up to two weeks, walnuts remain viable for a month and Kentucky coffee tree may remain viable for ten years or more.
A few species are so protected by their seed coats that they require special treatment before planting to get them to germinate. For a small number of seeds, this seed coat dormancy may be broken by mechanical means such as filing through the seed coat. Commercial nurseries often treat the seeds with acid or boiling water to break down the seed coat. Some species exhibiting seed coat dormancy are Kentucky coffee tree, persimmon, basswood and locusts.
For most seeds, fall planting is preferred to break internal dormancy with moist cold, so plant the seed in the fall for favorable growing conditions the following spring. A seedbed takes little space and can produce a large number of seedlings. Good seedbeds consist of well-drained soils -- a light sandy loam soil is best -- and located on a site mostly exposed to sunlight. The depth of planting is determined by size of seed; use a planting depth of two times the diameter of the seed. Cover the seedbed with fine mulch and water as needed. If predators (squirrels, mice, ground squirrels and chipmunks) are a potential problem, consider protecting the seedbed with a covering of hardware cloth to minimize seed loss.
In the spring, water the seedbed at intervals to prevent excessive drying. As the seeds germinate, adjust the watering to minimize damage from water-associated diseases such as the damping off fungus. A fungicide application may be necessary for small-seeded species such as pines and spruces. Grow the seedlings for one or two years and move the seedlings early in the spring to the desired location for the tree.
Rural forestry has started to look at direct seeding in fields as an option to traditional seeding planting. Tree seed (mostly oaks, walnut, ash, cherry and maple) is collected in the fall and either row planted or broadcast planted on field sites. One of the major advantages of seed planting may be increased density of the planting, resulting in less weed control and potentially better formed trees as the forest develops.
A simple recipe for broadcast planting is to till the soil and broadcast apply 10 to 15 bushels of walnuts and 3 to 4 bushels of acorns per acre. Disk the site to incorporate the oak and walnut. Follow this application with a broadcast application of a bushel of ash or maple seed followed with a light harrowing and packing. Depending on the sites and potential for weeds, herbicides may be applied after planting or soon after the trees emerge in the spring. Sites, which have at least 15,000 trees per acre, will often develop a closed canopy of trees after two growing seasons. Initial demonstration trials have shown that direct forest seedings result in trees with faster initial growth and better form than seedling planted sites. One possible disadvantage is that thinning may be required earlier in these direct-seeded forests.
Additional information is available from Forestry Extension Notes F-363, "Direct Seeding" and F-304 "Growing Seedlings from Seed" available from Forestry Extension, 253 Bessey Hall, ISU, Ames, Iowa 50011 or from Forestry Extension's Web site at http://www.ag.iastate.edu/departments/forestry/ext/planting.html.
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