Dr. Andy David, Associate Professor Forest Genetics
Whether you are collecting seeds to propagate from a favorite tree or collecting seeds from a seed orchard for future reforestation we all need to know the basics behind seed collection. Today we will cover four keys to successful seed collection: identification of fruit or cones, time of collection, ripeness of seed, and storage conditions.
First: Before you can collect seed you have to know what to look for. Does the species produce seed in a fruit, like acorns in oaks or samaras in maples and ash, or is the seed produced in cones like pines, spruce and fir. As simple as it sounds knowing what to look for helps immensely when it comes to forecasting seed crops or collecting seed.
Second: Knowing the proper time of year to begin collecting seed is also important. Most tree and shrub species ripen seed in the fall but some, such as serviceberry, red maple and silver maple, ripen seed in spring or early summer. All the conifers ripen seed in the fall but pines require two growing seasons before their cones can be collected. That means that there can be two cone sizes on pines, a small, green, immature first year cone (3/4 to 1 inch in length) and a larger cone that will contain ripe seed. When collecting pine cones make certain you collect the larger cones!
Third: Gauging ripeness of the cone or fruit is also important because if seeds are collected too early seed viability suffers. Conversely, if seed collecting begins too late then yield decreases as the seed is shed or consumed by animals. Physical cues to ripeness vary by species but generally involve a color change from green to tan or light brown. For example, in eastern white pine immature cones are green and as they mature begin to turn a light brown along the cone scale edges. When finally ripe the entire cone is a light brown. Samaras of both green and black ash are green throughout the spring and summer but begin turning yellow-green in August and then light tan and brown as the seed matures. Slicing individual seeds in half is an additional way to check ripeness. Seeds are ripe when there is a pronounced brown or black lining on the outside of the seed and the inside is white and moist but firm. Once the fruit or cones have been collected they should be inspected for insect damage. Distorted cone shapes, holes and excessive pitch are evidence of cone borers while small holes or pin head sized black spots are indicators of boring insects or fungi on fruits. For oaks or other species that produce hard mast crops the sink/float test can be used to judge seed soundness. Place newly collected acorns or nuts (with the tops on or off) into a pail of water. Those that sink are sound while those that float have been aborted or suffered insect damage.
Fourth: After the cones or fruit have been collected they have to be stored correctly to maintain seed viability. Newly collected cones or fruit should be stored in paper bags or burlap sacs until they can be processed for long-term storage. They should be kept cool and dry with plenty of aeration and never stored in plastic bags which promote mold and mildew.
Although it may be out of print if you can find it there is a very handy pocket sized book entitled Guidelines for Tree Seed Crop Forecasting and Collecting published by the Ontario Ministry of Natural Resources. For a more exhaustive treatment of seed extraction and long-term seed storage the Woody Plant Seed Manual, last updated in 2008 and available online at http://www.nsl.fs.fed.us/nsl_wpsm.html, is a wealth of information about general seed collection and storage techniques with additional species specific information on 236 genera from Abies to Zuckia.