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Germination


Most people are used to planting crop or horticultural seed. These have been bred to have high germination rates and to germinate quickly. Seed of native or wild plants are often not like this; if they were they would germinate at the wrong time and would not survive as seedlings. They have some kind of dormancy that must be broken by environmental cues that tell the seed that, based on prior evolutionary history and recent conditions, it should now be safe to germinate. There are also treatments, unlikely to be seen by a seed in the field, that work by apparently by-passing these normal field requirements.

Definitions of Natural Processes and Experimental Substitutes
  • Germination: Emergence of the seedling root from the seed coat
  • Seedling Growth: Development into a self-sustaining plant
  • Light Requirement: Small seed contain only enough stored energy to support just the start of seedling development, thereafter the seedling must capture its energy through photosynthesis. These seed delay germination until light intensity and light quality tell them that they are on the unshaded surface where they are likely to survive if they germinate
  • Dormancy: Lack of germination of viable seed even when all conditions (temperature, light, and moisture) are suitable for germination
  • Afterripening: Gradual loss of dormancy if the seed is not hydrated
  • Dry Aging: Dry storage at an optimum temperature for an extended time in order to afterripen the seed
  • Viability: Some seed remain alive for years in dry storage or while hydrated in the ground; some don't
  • Overwintering: Normal exposure of hydrated seed, in the ground, to a winter season. Some species may germinate, some may wait for warmer spring temperatures
  • Stratification: Experimental exposure of hydrated seed to extended cold. Assumed to mimic overwintering, but it also substitutes for other dormancy-breaking exposures such as passing through a warm summer (Winter Annuals)
  • Vernalization: Often confused with Stratification. Treatment of a plant to an artificial winter to induce precocious flowering in plants that normally flower only after surviving a season of winter (Winter Annuals, Biennials and some Perennials)
  • Double Dormancy/Complex Dormancy: Some seed (Hollies, Solomonís Seal, and others) require one or more cycles of several months of exposure as hydrated seeds to warm conditions followed by cold conditions. In short, they normally germinate only after a year or two in the ground
  • Hardening Off: For seedlings transplanted into soil, a protocol for gradually changing conditions from those required for immediate survival inside to those required to survive outdoors

  • Three Methods to Germinate Seed

    All protocols for breaking dormancy and supporting germination and seedling growth are essentially one of three Methods. Method One is to let nature do it, preferably to seed in a small pot rather than in the ground. This means having the seed in hand before the sequence of seasons that it normally requires for germination and enough outdoor space protected from sun (to keep the pots moist) and from rain (to keep the seed in their pots). Keeping the pots in trays and underwatering them greatly increases the success of this method. This is the best method for those who manage to get their seed well before winter and for those seed known to require overwintering.

    Method Two is to treat such pots of seed, sown usually in late winter or early spring, with protocols that substitute for the normal sequence of seasons that break dormancy and then to move the pots to the outdoors and handle them as in Method One. Fine if you have lots of refrigerator space for stratification of seed by refrigerating the entire pot. Not many of us are so lucky and the pots dry out quickly, even when wrapped or bagged. Some seed may germinate while in the refrigerator, so the pots have to be monitored for seedlings in need of rescue as well as soil in need of water. The method is for those who procrastinate in ordering their seed and for seed known to require little overwintering or for which overwintering requirements are unknown.

    The large advantage of Methods One and Two (dormancy-breaking treatments, germination, and seedling growth all in the same pot) is that it does not require transplanting into pots seeds that have been treated elsewhere or of small seedlings that have germinated elsewhere. No transfers are made and seedlings can grow large enough in their treatment/germination pot to easily survive transplanting to a larger pot or (shudder) into the ground.

    Method Three is for large number of seed. Treat the seed with dormancy-breaking protocols while they are in a small container and then transfer the seed to pots for germination and seedling development. We prefer putting small seed into baggies with a minimum of moist soil, storing them in the refrigerator for a month or so to break dormancy, and then distributing the soil+seed mixture onto the soil surface of pots destined for the outdoors where germination and seedling development will occur in the same pot as in Methods One and Two. Less refrigerator space, but monitoring is required as in Method Two. This is the method of desperation for those who procrastinated and then ordered way too much seed.

    Methods One, Two, and Three do not require Hardening Off of transplanted seedlings because they are not transplanted until they outgrow the pot in which they have germinated. Our experience with Hardening Off is that it takes a long time, continual attention, and only a minor fraction of seedlings of most species survive. Avoid methods that require Hardening Off if at all possible.

    Method Four (yes, I know) is for those who have to see what is happening to their seed, have to test a large number of treatment or germination conditions, or just do not have the space for pots that may never sprout seedlings. We sow seed on the surface of a semi-solid medium in a petri dish, refrigerate the dish to break dormancy and then transfer the dish to germination conditions where the seed will germinate while still in the dish. Then transplant the seedlings to pots. Getting the seedling out of the plate and into soil is often the challenge of this method. Then there is Hardening Off. Not recommended outside of a lab.

    Methods One and Two
  • Store Seed: Usually in a cool and dry place. If you wish to experiment with long-term storage of small seeds, put half of them in an envelope in a well-sealed baggie in a non-frost-free freezer.
  • Prepare Pots of Soil: Use bagged potting soil or soil-less potting mixture, without added fertilizer (most have ammonium nitrate which inhibits germination of most seed). Use normal particle size; it will be high mountains and deep valleys to small seed, but they do not mind. Do not use professional-type germination media that has a very small to small particle size; it drys out much too quickly. Saturate by underwatering and drain.
  • Sow Smaller Seed: Use a 4" x 6" plain note card, or a return-mail insert from a mag without much print on it. Fold in half lengthways and unfold. Tap the seed packet to distribute the desired number of its seeds onto the note card, reserving a fraction for possible resowing. Tap the note card to distribute seed onto the surface of the soil. Do not attempt to bury the seed.
  • Bury Larger Seed: Push them into the soil and brush soil on top of them. They should be no deeper than the thickness of the seed itself. They need not be covered. The objective is to have them in an unpacked soil with good contact of at least half their surface with the soil particles and the water that surrounds them.
  • Move the Pot to Field Conditions: Label the pot with tape and water-proof and sun-proof ink. Even the best of plastic markers somehow disappear by the time the plants are ready, or past ready, to be put in the ground. Protect from rain.
  • For Method Two, Move the Pot to a Refrigerator: First, place pot in a baggie or wrap it in foil or plastic. Look at it weekly, keep its soil moist, and remove it after a month (or earlier if seedlings appear).

  • For additional information about Methods Three and Four, see Seed Stratification and Seed Germination