I have often been asked how to germinate seed of a particular species, how to use gibberelic acid and many other related questions. I have written a short article here summing up my 20+ years of experience in sprouting seed. I hope you will find it useful. If you see room for improvement, please let me know!
Why start plants from seed? Aside from the enormous satisfaction of seeing young plants develop to maturity, many more plants can be grown from seed than from practically any other method such as taking cuttings or splitting bulbs, etc. The possible exception is tissue culture but this technique is beyond the typical hobbyist. Often, seed is the only way to obtain valuable plants. Besides, seed-grown plants are genetically different individuals and thus can set more seed, unlike clonally-propagated plants.
Germination failure often lies in the grower not knowing the exact requirements for a particular species and most seed lists don’t give a clue how to sprout their seeds. Here at ALPLAINS, we constantly run germination tests on the seed we offer and distill that knowledge into codes that accompany every seed packet. Many other people and agencies also run germination tests and publish their results in various books, pamphlets and websites, etc. which you are invited to study. Some of these are highly technical and may discourage the novice from getting started. If you are reluctant to grow plants from seed, feeling it seems too complicated or involved, then the goal of this article is to simplify seed-sprouting enough to give you the confidence to succeed.
Using only two basic techniques, called stratification and scarification, and various combinations thereof, you can sprout over 95% of the seeds listed in the ALPLAINS catalog. These techniques apply just as well for Asian, European and other seeds found on seed lists from the U.K., Czech Republic and Japan. There are plenty are challenging cases, to be sure, but just a little knowledge will allow you to sprout most kinds of seed and greatly increase the variety of plants growing in your garden.
Sowing the Seed
Before discussing the techniques, you need to select a way to sow the seeds. Most hobbyists and commercial nurserymen have their favorite sowing medium/potting system. What’s important is to sow seed indoors in a sterile medium in a protected area — sowing outdoors directly into the garden invites disappointment due to damage from insects, rot and frost. It’s true seeds sprout in their native habitat just fine but nature produces seed in vast numbers in the hopes that a few seedlings will survive to adulthood. We are more interested in obtaining the highest germination rate from our little seed packet. I use what was called Metromix 350, but is now sold under the name Fafard and consists of sphagnum peat, vermiculite and a wetting agent. This sterile material will absorb moisture even when bone dry. I mix about 4 parts of the medium with 1 part fine perlite. I used to sow in obsolete 7-1/2” X 5-1/2” styrofoam flats but now I use 4” square, plastic pots, fifteen of which press-fit into matching trays. I also use only pencil (0.7 mm) to mark the labels — the ink in those “permanent” markers fades after a year.
Do you sow the seed on top or bury it? Many seeds do require light to germinate, most others don’t care but very few actually require darkness. So I always sow on the surface except for large seed, e.g. Ipomoea, Paeonia, Sophora, Amsonia, etc. Flat seed like Asclepias, Yucca and Agave are best inserted edge-wise into the mix. Some growers apply a thin layer of very fine granite sand on top to discourage algae growth and stabilize small seedlings — I don’t bother. You can always add more mix to stabilize spindly seedlings if necessary. I keep the trays or flats in 4-foot by 4-foot wooden boxes (“warm box”) which have plastic roll-covers to keep moisture in. Heating cables provide bottom heat which suffuses through an inch-thick layer of silica sand (30 sieve.) Over each box is suspended a bank of five standard 4-foot fluorescent shop-lights. Everybody develops their own system but it’s important to be able to control the temperature and light. Of course, if you sow seed in your greenhouse, this equipment is unnecessary and you need only figure out a way to water the flats with a mist system.
Basic seed germination falls into three categories:
No pre-treatment — the absence of the requirement for either basic technique
All seeds must absorb moisture before germination can succeed. Once accomplished, seed sprouts in a relatively short period of time (days or weeks) at room temperature. Seeds in this category have neither a hard seed coat nor a requirement for cold temperatures. This corresponds to our “germination codes” (1) and (2) in the Legend.
Technique 1: Stratification
After absorbing moisture, seeds in this category require one or more shifts in temperature for certain lengths of time. Dry seed cannot be stratified! After sowing the seeds, I let the flats sit in the warm box for two or three days to allow them to imbibe moisture. Then I wrap the flats in plastic and place in a refrigerator I use solely for this purpose. Every week or so, I check the flats to see if any sprouts appear and return those to the warm box. Other species won’t germinate while cold so I return those flats to the warm box after a pre-determined length of time, whereupon sprouts appear a week or two later. Some species require “warm” stratification, that is, being held at 70 degrees for a certain length of time, then subjected to cold. Yet other species (fewer yet, thankfully) require more than one cycle of temperature shifts, often referred to as “oscillating temperatures” or “outdoor treatment.” This corresponds to our “germination codes” (3), (4) and (5) in the Legend.
Technique 2: Scarification
Seed sprouts only after the seed coat is nicked so that water can enter the seed. Germination then follows either with no further treatment (usually) or requires stratification (rarely). Sandpaper (fine grit) is suitable for most cases by dragging the seed along until you see a color change (endosperm exposed.) Some seeds are encased in a water-resistant membrane. Merely a variant of scarification, these membranes can be easily removed by rubbing between the bare or leather-clad palms, revealing the often different-looking seed inside. Castilleja, Chionophila and some Penstemon species are good examples of this type. Note these are all genera in the Scrophulariaceae family. This corresponds to our codes “R” for rub or “S” for scarify in the pre-treatment codes (d) in the Legend.
Table of Genera by Category
I list here the family, genera or species in the ALPLAINS catalog by which germination category they fall into:
No pre-treatment: Agastache, Agavaceae, Aloinopsis, Antimima, Arbutus, Artemisia, Aster, Bouvardia, Buddleia, Calandrinia, Calylophus, Calyptridium, Centaurium, Cerastium, Chamaebatiaria, Chamaechaenactis, Chilopsis, Clementsia, Crassula, Delosperma, Dianthus, Dracocephalum, Dudleya, Enceliopsis, Ephedra, Erigeron, Haplopappus, Heuchera, Houstonia, Hymenoxys, Lepidium, Leucophyllum, Ligularia, Mimulus, Monarda, Monardella, Oenothera, Origanum, Penstemon hallii, P. harbourii, P. clutei, Petrophyton, Physaria, Potentilla, Ramonda, Salvia, Sedum, Silene, Talinum, Townsendia, Yucca, Zauschneria, Zinnia.
Stratification: Abronia, Acaena, Adenophora, Aethionema, Akebia, Allium, Amsonia, Androsace, Anemone, Anemonopsis, Angelica, Antennaria, Apiaceae, Aquilegia, Arabis, Arctomecon, Arenaria, Argemone, Arisaema, Asarum, Asclepias, Asyneuma, Balsamorhiza, Berberis, Calochortus, Caltha, Camassia, Campanula, Cardiocrinum, most Cactaceae, Castilleja, Cercocarpus, Chaenactis, Chimaphila, Chionophila, Claytonia, Clematis, Collomia, Corydalis, Cryptantha, Cusickiella, Cymopterus, Delphinium, Dicentra, Dodecatheon, Douglasia, Draba, Echinacea, Eriogonum, Eritrichium, Erysimum, Erythronium, Fraxinus, Fritillaria, Gentiana, Gilia, Hulsea, Ipomopsis, Iridaceae, Kelseya, Leptodactylon, Lesquerella, Lewisia, Lilium, Linum, Mertensia, Paeonia, Parrya, most Penstemon spp., Phlox, Polemonium, Primula, Pulsatilla, Salvia, Saponaria, Saxifraga, Scutellaria, Stachys, Synthyris, Trollius, Veronica, Viola.
Scarification: Amorpha, Arctostaphylos*, Astragalus, Baptisia, Caesalpinia, Callirhoe*, Caragana, Cassia, Ceanothus*, Cercis*, Dalea, Iliamna, Ipomoea, Lathyrus, Leucocrinum*, Lupinus, Sphaeralcea, Sophora, Oxytropis, Pelargonium, Trifolium. Note: an asterisk (*) following indicates the need for stratification as well.
In examining this matrix, some patterns begin to emerge: seeds that require scarification belong to hard-shelled families such as Convolvulaceae, Fabaceae, Malvaceae and Ericaceae. These seeds are often as hard as small pea-gravel. Unfortunately, habitat is not an accurate predictor of seed germination type. The seeds of many alpine species come up easily with no pre-treatment whereas many lowland species still need stratification. However, seeds of warm deserts generally sprout with no treatment, except perhaps scarification.
In view of all of this information, I have tried to codify it as simply as possible into “germination codes” for each species offered in our catalog, as explained on the Legend page of this website.
Listed here is a more complete explanation of the germination codes and how they relate to the techniques mentioned above.
Here is a typical listing:
Penstemon utahensis (Scrophulariaceae) (36x15, Z4, P, RGL, 3:8w) …......………….. 40 seeds / $4.00
The germination codes are the last two groups of codes (d) and (e) above. The codes in (d) refer to any pre-treatment of the seed before sowing such as light requirements, scarification or gibberelic acid. The codes in (e) refer to the requirements after the seeds have soaked up water.
Codes (1) and (2): No cold stratification necessary. Seed requires no pre-treatment. Code (2) simply refers to the tendency of some species to germinate in “flushes.” In nature, if all seeds germinated when conditions suddenly became favorable, and then a hard freeze occurred, the entire population could be wiped out. Thus, seed populations often exhibit the phenomenon of “staggered” germination, where only a portion of the seed bank sprouts when conditions permit. Unsprouted seeds may lie fallow for a few months or another year until conditions are once again favorable and a portion of the remaining seeds sprout, and so on. It’s nature’s way of hedging its bets. Seeds of cacti and desert shrubs frequently exhibit this behavior. Inconvenient for us as gardeners but we can speed up the process usually by pricking out all of the sprouts from the first flush, grow them on in another pot and then allow the original flat to dry out naturally. After a week or two, re-wetting the medium often brings up another flush of seedlings. This process can be repeated until the overall yield is satisfactory.
Codes (3) and (4): Cold stratification required or is helpful. After spending time in the cold for a certain number of weeks as indicated (for example, 8 weeks for Penstemon utahensis), sprouts should appear after exposure to warmth or may appear while still cold. Code (4) refers to the more difficult or time-consuming (recalcitrant) seeds, where several cycles of cold, then warmth, etc., may be needed to sprout them. This process, as mentioned earlier, is often termed “outdoor treatment.”
If you are just beginning your adventure into the wonderful world of seed germination, I suggest you start with seed requiring no pre-treatment (Code (1)) to gain confidence and to increase your skill in growing on the resulting seedlings into mature plants. Naturally, as your interest grows, you may want to learn about other techniques in seed germination to handle more challenging cases. Probably the most useful of the minor techniques is:
Gibberelic Acid (GA3): much has been written about this growth hormone. Most seed does NOT require treatment with this chemical and only results in dead seed or weak, spindly seedlings which quickly rot. The seed of some cacti, rosulate and sagebrush violets, Glaucidium, Aquilegia jonesii and other calciphiles do indeed benefit from GA3 treatment, but if you working on these cases, then you have reached a level of sophistication which should yield success.
Since I have often been asked how to use GA3, I will outline my procedure here. First, the seeds to be treated must absorb a solution of GA3. I never pre-mix GA3 with water because it does not keep long. Solid (powdered) GA3 keeps indefinitely and I mix it with water on the spot when needed. I use small, glass, 2-cc (cubic centimeter) vials (about an inch tall) with tight-fitting lids. I get these by the hundred, including the powdered GA3, from my local chemical supply house. I made a rack to hold the vials from a piece of particle board shelf by drilling a matrix of 1/2”-deep holes on 2-inch centers. Masking tape between the rows allows for easy labeling. Every vial gets its own batch of seed to be treated and I then add an amount of GA3 that fits on the tip of a small chemist’s spatula (equal to about several grains of salt). Using a dropper, I add warm water to about half-fill the vials and let them all stand overnight in a warm place. By the next day, the water will have absorbed the GA3 and the seeds will have absorbed the solution. It can stand for another day but after that, rot usually begins. Each vial then needs to be flushed out into a beaker and sown. Swirling the beaker while dumping the seed/solution mix onto the sowing medium takes some practice to equally distribute the seeds but is the fastest way to complete the chore. The seeds can be drained and dried briefly but must be sown and watered immediately. The flats are then ready for further treatment (stratification.) Using GA3, close to 100% germination results on Viola beckwithii, V. trinervata and other sagebrush violets.
Dry storage of some seed types (especially Cacti) actually increases germination yield and decreases the necessity for GA3 because germination inhibitors are destroyed as the seed ages. For instance, after 2 years of dry storage, Maihuenia poepiggii seed sprouts in a few days without the need for GA3.
1) Norm Deno, Seed Germination Theory and Practice, 139 Lenor Drive, State College, PA 16801
No longer available directly from Norm Deno.
2) Dara E. Emery, Seed Propagation of Native California Plants, Santa Barbara Botanic Garden
3) Alpines ‘86 Publications Committee, Rocky Mountain Alpines, Timber Press, Portland, OR 97204
4) Peter Loewer, Seeds, The Definitive Guide to Growing, History & Lore, Macmillan, NY 10019
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