J. L. HUDSON, SEEDSMAN, BOX 337, LA HONDA, CALIFORNIA 94020-0337 USA
HOW TO GERMINATE SEED
Your best source of information on the germination
of seeds is 'Seed Germination, Theory and Practice' by Norm Deno. It lists 4000 species and gives
pretreatments if any, and detailed instructions on the use of GA-3. Two supplements listing
additional species have been published. This book will absolutely increase your success with seeds! NOTE: We do not sell Deno's book - and Deno has ceased
publishing. The book is now available as a PDF Download:
Seed Germination: Theory and Practice (12 mb)
https://www.jlhudsonseeds.net/Seed%20Germination%20Theory%20and%20Practice-Deno.pdf
First Supplement to Seed Germination: Theory and Practice (5 mb)
https://www.jlhudsonseeds.net/Seed%20Germination%20Theory%20and%20Practice%20Supplement%201-Deno.pdf
Second Supplement to Seed Germination: Theory and Practice (5 mb)
https://www.jlhudsonseeds.net/Seed%20Germination%20Theory%20and%20Practice%20Supplement%202-Deno.pdf
GENERAL RULES of SEED SOWING
Seeds need water and oxygen to germinate, so are best started in a light, loose soil that will
not compact, get soggy, or crust over. Free flow of water and air are a must. Cover seed with 2 -
4 times their thickness of soil, unless they require light to germinate. Sow shallowly in cold wet
spring, more deeply in warm dry summer. Large seed can be soaked overnight and planted singly.
Barely cover small seed, and sprinkle fine seed on the surface and water by misting. Plant flat seed
edgewise and winged seed with wing uppermost or broken off. Sowing too thickly wastes seed and
weakens the crowded seedlings, but some kinds sprout best if crowded. Lightly tamp soil to insure
good contact with the seed, unless heavy. Keep soil moist, not soggy, and do not allow to dry out.
Common causes of failure are soil too heavy, wet or cold, or allowed to dry out, not giving slow
seeds long enough to come up, pests eating the seeds or seedlings, and not giving dormant seeds the
proper pretreatment. Careful attention to the instructions in the catalog and on the packet will
help insure good results. Common causes of seedling loss are damping off due to poor air circulation
and overwatering, drying out or burning due to placing in full sun or outdoor conditions too
quickly, transplanting shock (best done on a cool, moist day), and predation by insects, slugs and
snails at night.
TEMPERATURE
Most seeds germinate best at warm (70°F) temperatures. Plants from temperate regions, the
arctic, high mountains and high deserts often germinate best at cool temperatures. Plants from
winter-rain areas like California, the Mediterranean, Chile, S. Africa and parts of Australia also
like cool temperatures. Warm temperatures will often speed germination of these seeds, but lower
vigor and survival. Warm desert plants and tropicals like warmth. Temperatures used in the catalog
are: Cold (34 - 45°F), Cool (50 - 65°F), Warm (65 - 80°F) and Very Warm (80 - 100°F). When no
temperature is given, warm (70°F average) is indicated.
TIME UNTIL GERMINATION
Average range of time to germinate is usually given in weeks. A seed that takes 2 - 3 weeks will
usually come up fairly evenly; one that takes 1 - 12 weeks will tend to straggle in irregularly.
Time varies with temperature, so expect considerable variation. Don't give up too soon—many who
have given up and sown another seed in the pot end up with two types of plants in the same pot!
HARDY ANNUALS (HA)
These will stand some frost and can be sown direct to the garden as early as the ground can be
worked, March to June. Prepare the soil until a smooth, fine surface is obtained. An attractive
annual border can be had by planting in large, irregular drifts.
HALF HARDY ANNUALS (HHA)
These are killed by frost and should be sown in late spring after danger of frost. For early
bloom, start early indoors and plant out after danger of frost.
TENDER ANNUALS (TA)
These need warmth and shelter and are best started in pots or flats and planted out in favored
spots after the soil has warmed.
BIENNIALS and WINTER ANNUALS
Biennials are sown like half hardy annuals or perennials in spring or fall and planted out in
September and October. Winter annuals such as some Californian and desert plants may be grown in
summer, but are at their best sown in fall, even if grown in the greenhouse in cold winter areas.
HARDY PERENNIALS (HP)
Many of these germinate readily at warm temperatures, and can be sown direct to the garden or
early in the greenhouse or cold frame. If started early, they often bloom the first year. Others
germinate best at cool or cold temperatures and the seedlings need cool temperatures. Many have
various dormancies and need the pretreatment indicated.
HARDY TREES and SHRUBS
Many will germinate readily if sown in spring. Others need cold or other pretreatment, and some
are best sown in fall or winter and covered with a mulch or snow. The addition of some forest soil
or litter from below both hardwoods and conifers is often very beneficial, greatly increasing
seedling growth due to beneficial mycorrhizal inoculation.
TROPICAL and SUBTROPICAL PLANTS
These often need very warm temperatures. Bottom heat and constant moisture are often beneficial.
Some take surprisingly long times to germinate. Many people think all tropical seeds are short-lived
and perishable, but many of the longest-lived seeds are tropical, and some even need to be aged dry
for a year before they will germinate!
CACTUS SEED
Sow cactus seeds on the surface of a well-drained mix, and barely cover with
more soil, a little coarse sand, or some chick-grit. Keep moist by misting until
germination begins, then reduce humidity. Keep seedlings in part shade until
well-developed and looking like cacti. Pot up when 1/2 - 1" in size. Deno
found that 2/3 of the cactus species he studied need GA-3 to sprout, and some
need ageing for a couple of years before they will germinate.
AQUATIC PLANTS
We have had the best results with some of these by sowing in pots, pans, or petri dishes, and
submerging so that the soil is under 1/4" of water.
FERN SPORES
Spores should be scattered thinly on the surface of a light, sterile, peaty mix which has been
watered with clean sterile water about 4 hours before sowing. Cover pot with a pane of glass or
enclose in a plastic bag and place out of direct sunlight. A light green film will form on the
surface in 1 - 4 weeks or so, up to 6 months for slow species. Botrychiums may take up to 8
years, and one Equisetum takes 18 years! Small round or heart-shaped prothallia will then
form. Begin to mist lightly with distilled water weekly to enable fertilization of the egg cells,
until true fronds develop. Transplant sporelings when large enough to handle. Good ferns can usually
be had in 8 - 12 months from spores. Ferns are hybridized by sowing 2 kinds of spores together.
SOIL MIXES
Many seeds do well sown direct to ordinary garden soil, but even good soil may be poor in pots
or flats. These need a lighter, looser soil. Most commercial mixes are fine, but the addition of
some garden soil and compost will often insure adequate beneficial micro-organisms
and fungi, A
good soil mix can be made at home from 1/3 garden loam, 1/3 peat or compost, and 1/3 gritty sand.
Number 1 limestone chick-grit makes a good top dressing for many alpines or slow germinating seed to
discourage algae growth. Crushed charcoal also helps.
HARD SHELLED SEED
These have hard impermeable shells and need nicking or scratching the coat to allow water to
enter and the seed to germinate. The best results are from the least amount of nicking that will
allow water to enter and the seed to swell. Many failures are due to over-nicking and damaging the
seed.
Different seeds need varying amounts of nicking. Most do best with lightly rubbing on sandpaper or a
file until just the very outer coat is scratched. Often just scratching with a knife-point or
scriber works. Others need serious nicking, sometimes with a hacksaw until the white interior shows.
Nicking seed one by one can be tedious but is most effective. Larger lots can be rubbed between two
boards covered with sandpaper, or shaken or tumbled in a can lined with sandpaper. Then soak the
seed overnight and any that don't swell or soften should be re-nicked and soaked again until
swollen.
NICK and SOAK means nick first, then soak, and re-nick any hard (unswollen) ones.
SOAK and NICK UNSWOLLEN means the seed is usually only partly hard and many will swell without
nicking. Soak first, nick only the hard ones.
OTHER METHODS for large lots include:
Hot Water Soak: The seeds are placed in a cup and not quite boiling (200°F) water is poured on them
and allowed to cool and the seeds to swell. At least 4 - 5 times their volume of water is used. Or
the seeds are dipped in boiling water for 10 seconds to 3 minutes. Gives great
results with some species, others are damaged by the treatment.
Dry Heat: The seeds are baked dry in an oven at 140° to 220°F for 4 - 10 hours, or are microwaved
for 30 seconds to 4 minutes. Gives erratic results.
Sulfuric acid or lye soaks work with some seeds.
COLD TREATMENT (Prechill)
Many seeds need a cold moist period before they will sprout. The essentials are moisture, air,
cold and time. Dry cold (a packet in the refrigerator) won't work. Often the seed may be sown in
fall or winter and allow natural cold and snow to work.
1. Soak seed overnight until swollen or soft (up to four days for large hard nuts). Nick if needed.
2. Mix seed with about 3 times its volume of damp peat moss or vermiculite and place in a plastic
bag or pill bottle. Small amounts may be conveniently layered between damp paper towels or coffee
filters. Remember, air is essential; avoid sogginess. Label the bag with the name of the seed and
date to be removed from cold. Mark your calendar too!
3. Store in the refrigerator (34 - 40°F) for the time specified in the catalog. Four to 12 weeks is
usual.
4. Remove the seed and sow. Seed is best kept cool (50°F or so) for a week after sowing, and
gradually brought up to warm temperatures. Warming too quickly can be fatal for some seeds.
'Cold germinators' only sprout at cold temperatures, and are most conveniently treated by layering
in damp towels and pricked off as they germinate.
If using outdoor treatment, hold pots at above freezing for a few weeks before putting outside.
Snow cover is often highly beneficial.
Dormancy is highly variable. Sometimes a seed collected in the warm lowlands will germinate readily,
but the same species collected at a high elevation will need cold. Dormancy even varies between
individual plants at the same site, and varies with weather before harvest and conditions of storage
after harvest.
GIBBERELLIC ACID-3 (GA-3)
GA-3 is a naturally occurring plant growth regulator. Presoaking seeds in GA-3 will often cause
rapid germination of many highly dormant seeds that would otherwise require cold,
ageing, light, or
other prolonged treatments. Many different types of dormancy are overcome. You may buy our 'GA-3
Primed' seed which are ready to plant, or the GA-3 powder, or one of our kits. GA-3 is safe, easy to
use, economical, and rapidly becoming a standard tool for germinating seeds. For more information,
see our 'Gibberellic Acid-3
Information Sheet', which gives full details of its use, or get Deno's
books.
SMOKE and FIRE TREATMENT
Smoke treatment often helps germination of plants from fire-prone environments, particularly
Mediterranean-climate plants such as many species from California, Chile, Australia, South Africa,
and the Mediterranean region. For a list of genera that have responded to smoke treatment, click
here: Smoke Genera.
Prepare a dilute smoke solution by adding one part commercial smoke flavoring to nine parts
water. Either soak the seeds in this solution overnight (or until they swell), or water the pot
or flat once with this solution. Smoke flavoring is found in the spice and flavoring or
barbecue section of the grocery store . It comes in small brown bottles of liquid, called
"liquid smoke" or "hickory seasoning". Look for the "all natural" type
that lists only water and natural smoke concentrate as ingredients. "Wright's" is the
brand we find out here in California.
Smoke treatment is still experimental, and you may have to try different dilutions. Let us know your
results!
FIRE TREATMENT: Sow in a flat or pot and cover with several inches of pine
needles or heavy straw. Burn this and leave the ash and charcoal in place, and
water the flat as usual.
OTHER TREATMENTS
DRY STORAGE or AGEING: Many seeds will not germinate when freshly harvested, but are dormant
until after a period of dry storage ranging from 1 - 12 months or up to 5 years. The time varies
with temperature, humidity and oxygen. We try to supply aged seed whenever necessary. Often this
type of dormancy can be broken with GA-3.
WARM MOIST TREATMENT: Many seeds need 1 - 4 months of warm moist treatment, followed by cold
treatment to sprout. In some, the root sprouts during the warm period, but the shoot does not sprout
until after a cold period (epicotyl dormancy). Called 'two-step' germinators by Deno. Some of these
have unformed embryos which must first develop at warm temperatures. Some seeds are '70 - 40'
germinators, which need warm moist, then cold moist, and germinate at cold temperatures. Some
tropicals which are slow to germinate (many palms and aralias) need prolonged warmth to first
develop their embryos. Many seeds are 'multicycle' germinators, needing several cycles of cold and
warm periods.
SOAKING, WASHING or LEACHING: Many seeds contain germination inhibitors which in nature prevent the
seed from germinating except during the wet season (tropicals) or only after sufficient rain has
fallen (desert plants). Soaking the seed in shallow water and changing every day for several days
will leach out inhibitors. Heavy daily watering of pots may work. Some have oily coats and need
detergent or peroxide soaks.
LIGHT or DARKNESS: Some seeds need light to germinate; others need darkness, and light prevents
sprouting. If light is required, sow on the surface; if darkness is needed, cover seed well.
OSCILLATING TEMPERATURES: Some seeds need the daily change from warm to cold that occurs in spring
and fall, and they germinate best sown in pots and exposed to outdoor conditions.
OTHER TREATMENTS: Soaking seed in potassium nitrate (KNO3), hydrogen peroxide, citric acid, sodium
hypochlorite (bleach), smoke solution, charred wood leachate, or enzyme solutions have all been used
to trigger germination of seeds. See our Gibberellic Acid-3 Information Sheet for brief tips on experimenting with these
treatments.
PLASTIC BAG METHOD
Best for very slow to germinate seeds, very tiny dust-like seeds that can't be allowed to dry
out, and very slow-growing seedlings. Small clean pots are filled with damp, sterile, soilless mix.
Milled sphagnum or a light dusting with powdered charcoal discourage fungi and algae. Seeds are
sown and the whole pot is sealed in a plastic bag and placed out of direct sunlight. This creates a
mini greenhouse and the soil will not dry out and the seeds are protected from mice, etc. Pots can
be left for years with no care other than regular checking for seedlings. As soon as seedlings
appear, begin hardening off. Bagged pots may be kept under fluorescent lights without overheating.
Don't forget to label!
HARDINESS ZONES
The rating of plants according to the hardiness zones in which they will grow has improved
greatly over the last twenty years. They are fine for common, widely grown plants, but for most
plants, our knowledge of their ecological limits is incomplete. Too often, the assignment of zones
is merely educated guesswork. Many plants will do well far outside their usual ecological range, or
seeds collected at the species northernmost limit will be much hardier than usual. Also, a heavy
mulch, or planting by a south-facing wall, or other simple tricks can greatly extend a species range
in cultivation. So don't rely too much on the zone numbers, or let them prevent you from
experimenting!
THE LIMITS OF THE AVERAGE ANNUAL MINIMUM TEMPERATURES FOR EACH ZONE
Zone 1: Below -50°F
Zone 2: -50° to -40°F
Zone 3: -40° to -30°F
Zone 4: -30° to -20°F
Zone 5: -20° to -10°F
Zone 6: -10° to 0°F
Zone 7: 0° to 10°F
Zone 8: 10° to 20°F
Zone 9: 20° to 30°F
Zone 10: 30° to 40°F
SEED LONGEVITY
Many people have the mistaken idea that seed must be very fresh to grow, and the occasional
failure of a packet is blamed on 'old seed'. Properly stored, seed of most species is viable many
more years than most people would expect, some giving high germination for decades. Though some
species are short-lived, many others are dormant when freshly harvested, and actually need an
ageing period of weeks, months, or even years before reaching full germination. Therefore I am including
information on the longevity of various seeds. As my long-time customers know, I have trouble
obtaining enough of many scarce seeds to keep them in stock for a single season, much less have
carryover from one year to the next! And all of my seeds are stored in glass jars in a low humidity
atmosphere, ideal for preserving viability. Should you find you need to store some seed till next
season, keep the packets in a well closed glass jar in a cool dry place.
Seed half-life is frequently given in the catalog. This is the average number of years it
takes for seed of that species to drop to half of maximum germination, when stored under ordinary
conditions.
"In several cases, maximum germinability was not attained until after some years of
storage."—D. A. Priestly, in describing a longevity study of 36 species of common seeds.
It was found that 14 of the 36 species retained half their viability for ten years or more of
open storage.—J.L.H., 11/87.
ABOUT DIFFICULT SEEDS
Over millions of years, wild plants have evolved germination strategies which ensure their
survival, but which may not be convenient for the home gardener who wants a quick and even stand of
plants from a packet of seed. Many seeds sprout irregularly, so that if the first flush of seedlings
is killed by adverse weather, insect predation, etc., more will come along to take their place. In
adaptation to various environments, some seeds need periods of cold, warmth, darkness or light,
fire, etc. Some have seedcoats of varying hardness or impermeability, and others contain chemical
germination inhibitors which must be leached from the seed before it can sprout. Some species
disperse themselves over wide areas by being eaten by animals, the seed sprouting far from the
mother plant, the seedcoat softened by digestive juices. Many seeds have internal clocks, and give
much higher germination at certain times of the year, regardless of the treatment given. All seeds
wait for the correct time and conditions before sprouting, and the gardener must mimic those
conditions to ensure successful germination.
We are continually testing seed for germination, and conduct research into improving methods of
handling difficult species. For slow seeds, which take months or years, making a standard test
impractical, we may use 2,3,5-triphenyltetrazolium chloride to test for hydrogenase enzyme activity,
which quickly indicates whether there is a living embryo in the seed. It can take years of research
to determine the best ways to germinate a specific species. Oryzopsis seed has been studied
for over 50 years, yet we still do not fully understand its requirements. Even then, seed collected
from one population may germinate readily, yet the same species gathered in a cold-winter area may
need cold treatment.
We offer many seeds which are easy, and sprout quickly and evenly. But with some you must be
prepared to experiment, be patient, and use your initiative and intuition. Remember that with some
rare species, you are venturing into unknown territory. Most corporate seed companies will not carry
difficult seeds, only selling, easy, mass-produced varieties. We like to offer a more challenging
alternative.—J.L.H. 11/89.