You may find that the
easiest and least expensive way to obtain many native species is to grow your
own. You don’t need to be an
expert or own a greenhouse to propagate native plants. By choosing more promising plant
material and paying attention to some simple details, most gardeners should be
able to grow many native species from seeds or cuttings.
When we propagate plants, we
are facilitating natural processes that plants do all by themselves.
Understanding a bit about the reproductive biology of plants can help to improve our success in
harnessing these processes.
There are two categories of
plant multiplication in nature, and in horticulture: vegetative and sexual reproduction.
When plants multiply
vegetatively- through stoloniferous growth in nature, or in propagation from
cuttings, layering, etc.- all of the resulting plants will be genetically
identical, though they may be completely separate physically.
When plants grow from seed,
genes get shuffled around and the offspring will be similar, but never
identical, to the parent plant(s). This is sexual reproduction.
Growing natives from seed
Many plants have hermaphrodite (in botanical floras, these may be termed “bisexual” or “perfect”) flowers- male and female parts in the same structure. Dioecious plants have separate female and male flowers on different plants (Aruncus dioicus, Goatsbeard). Some species (including several of our native Sidalceas) have a gynodioecious system: some plants have hermaphrodite flowers and some only female flowers.
Many plants have hermaphrodite (in botanical floras, these may be termed “bisexual” or “perfect”) flowers- male and female parts in the same structure. Dioecious plants have separate female and male flowers on different plants (Aruncus dioicus, Goatsbeard). Some species (including several of our native Sidalceas) have a gynodioecious system: some plants have hermaphrodite flowers and some only female flowers.
Many plants with
hermaphrodite flowers are capable of selfing: that is, the flower can
self-pollinate. Some will only self, some possess mechanisms that encourage
outcrossing (pollen morphology, arrangement of male and female parts, genetic
self-incompatibility etc.) and some do both with equal facility. Outcrossing
increases genetic variation and thus population fitness; selfing ensures
reproduction when populations are very small and isolated or pollinators are
scarce.
Seeds can usually be
collected for home garden use without impacting wild plant populations. Never decimate the seed output of a
small wild population. Most seeds
are ripe when they turn dark brown or black (sometimes red) and capsules or
pods are turning brown and papery, and/or opening up. Some seeds will be spilled almost immediately by the plant,
while others may be retained in pods longer. A few (including many in the daisy family, and others like Asclepias and some of the Mallows) will continue to ripen days or weeks after the
flowering stem has been cut from the plant.
One problem about collecting
wild seed is that plants are often hard to identify by the time the seed is
ripe. When you find plants in bloom from which you want to collect seed, ake
notes on their locations , flag them, and return when seeds are ripe- a few
weeks to a couple of months.
In general, best germination
is obtained from seeds planted the same year they are shed, but when stored under
cool, dry conditions, most will last several years (particular larger seeds, seeds
in the legume family, etc.) A few
species need to be planted very soon after ripening (e.g. Trillium and possibly Delphinium).
Many seeds, particularly in
temperate and colder regions, possess dormancy mechanisms to delay germination
until conditions are favorable. Timing, day length, temperature, light
conditions and available moisture may be factors in a seed’s readiness to
germinate. In nature, some seeds rely upon being consumed and then passed
through the GI tract of animals, and so there may be a hard seed coat or fleshy
covering that needs to be broken down before germination can occur.
Many seeds, including most
natives, benefit from pretreatment.
For some plant species with
thick, hard seed coats, additional pretreatment will include some kind of
mechanical or chemical action on the seed coat prior to planting. This can be
accomplished through presoaking in water for 24 hours, fermentation, or
“scarification”- gentle nicking with a blade or abrasion with sandpaper (e.g.
Lupine).
Some seeds with fleshy
coverings must be washed thoroughly before other pretreatment or planting, as
the covering may contain germination-retarding compounds. Other fleshy fruits must be fermented
to facilitate seed germination.
Most PNW and other
cool-temperate region species require or greatly benefit from a period of cold
to break dormancy. This means at minimum several weeks of exposure to cold.
This feature of dormancy ensures that germination will occur in spring, giving
seedlings the chance to mature before the following winter.
Stratification is a method
of storing seeds dry in the freezer or (preferably) moist in the refrigerator,
often in moist peat, vermiculite or sphagnum moss, or on damp paper towels.
Published protocols for various species advise weeks or months of
stratification.
Vernalization is the easiest
approach by far: just plant out the seeds in pots or flats of soil, and leave
them outdoors over winter. In many
species, germination will commence in spring. In some species (including Lilium spp, Trillium spp, Iris tenax, Cornus
canadensis, Delphinium menziesii), two
springs must pass. This is called double dormancy. Germination occurs under the
soil, usually with no aboveground sprout until the following year. The process
may sometimes be sped up by “tricking” the seed with a second period of cold
stratification in mid-summer.
Most seeds can be planted in
good quality potting soil, or a mixture of potting soil and seed starting
mix. A soilless mix may be
preferred for some plant species that are prone to fungal diseases. The mix is
sterile and provides excellent drainage, but contains no nutrients, so that
seedlings must be pricked out and transferred to real soil as soon as true
leaves appear.
For more durable seedlings,
it’s fine to plant all seeds in a single flat filled with soil. Place seeds about two inches apart and
don’t leave them in the flat so long that they begin to
entwine their roots. They can be
scooped out individually for transplanting to 4” pots—my favorite tool for this
task is a teaspoon.
Planting seeds individually
into recycled sixpacks or into plug trays greatly facilitates transplanting,
and protects delicate roots of seedlings that resent transplanting. These include many tap-rooted plants
like Eriophyllum, Asclepias and some Malvaceae, and those with latex in their
stems, notably anything in the poppy family (e.g. Eschscholzia, California Poppy) and the Apocynaceae (Asclepias).
The two most common causes
of disappointment for novice seed planters are:
1. covering the seeds with
too much soil and
2. allowing seeds to dry out after they have begun to
imbibe moisture.
The general rule for
planting depth is that seeds should be covered with no more soil than a depth
equal to the shortest dimension of the seed—that is, for an oblong seed that is
.2 mm by 2 mm, planting depth is .2 mm.
Thin, papery seeds (as many Asteraceae and Lilium)
should have just enough soil on top of them to conceal them from view; very
small, round seeds are surface-sown. Seed that is so fine it’s hard to see or
to handle with precision can be evenly mixed with fine sand to facilitate even
sowing.
Always sow into damp soil,
and tamp down carefully. Check protocols for your particular species; some
seeds (often very small) require continued exposure to light; these are
surface-sown and pressed lightly into the medium.
Disappointments can also
arise from seed loss due to soil disturbance, rain splash, insect or bird
predation, etc. Covering outdoor
seed containers with cloches of fine-grid poultry netting or (preferably)
hardware cloth will break the fall of rainwater and discourage foraging birds.
Once germination becomes
possible in spring, the soil surface in seedling containers should be kept
evenly moist at all times. Never
allow it to dry out, even briefly, as seeds that have begun to “imbibe” (absorb
water) will die if they have not produced enough root to reach down to moisture
retained lower in the soil. Water
carefully with a fine spray or mist, to avoid seed loss through splashing or
washing seeds across the soil surface.
In warm weather, watering may need to be done several times a day.
Conversely, take care not to
over-water, as this encourages competing hitchhiker plants (moss, liverworts
and algae), can rot seeds or fledgling roots, and can contribute to fatal
diseases such as the damping-off fungus.
If you see algae on the soil surface, you’re definitely over-watering.
When germinating seeds in
containers, bottom heat may be helpful.
The internet provides information on use of horticultural heating mats
(which greatly resemble old-fashioned water bed heaters), or coils. I have found the flat top of my
electric hot water heater to be perfect, and have also used a conventional
heating pad used for home treatment of aching muscles, etc.
Continue to protect seedling
containers with hardware cloth cloches until the young plants begin to grow
up. Keeping flats on an elevated
surface is most important in spring and summer, to help protect from insects
and pets. Slugs in particular are
most fond of young seedlings.
For most plants,
transplanting carefully to another container may be possible once at least two
true leaves (the ones that follow the first leaves, the cotyledons) have
emerged. Keep seedlings in strong,
direct light, and keep them evenly moist, with some warmth and always with
protection from freezing and from insects.
Once seedlings have two true
leaves, you can start fertilizing VERY gently. Dilute your standard mixture for containers by at least 3:1
with additional water.
Many annual
native wildflowers like Sea blush germinate in fall and overwinter as
frost-hardy small plants. In
spring, they take off and gain height before blooming, setting seed and
dying. All their energy is put
into seed production, with none left over for permanent roots. If you want these wildflowers for the
next year, you must let them mature and dry their seeds. Most will self-seed in the same place,
and if you want a patch elsewhere, collect seed heads before they shatter and
dry them in a paper bag or scatter the heads in the new location. If you save seeds, plant them in fall
to early winter so they can begin the next cycle.
Perennials generally delay germination until spring, after
their vernalization period over winter.
California poppies act somewhat like both annuals and perennials, self-seeding, germinating
in fall, overwintering more or less successfully, and blooming all the next
summer. For most perennials seeded
in fall, you can prick out small plants in late spring or summer as they get
several true leaves, and pot them up into 4” pots, moving them to larger pots
as they grow. Or you can thin them
in the flats, just so each plant has some growing room.
Perennials invest in root
structures and return year after year, sometimes dying down to the ground in
fall. Some are short-lived
perennials, like our native Red columbine, returning for a few years, then dying
out. Keep planting seeds for
replacement plants.
Serendipity, happy accidents, can bring you gifts of free
plants, especially after you get started with native plants in your
landscape. Bird droppings deliver
seeds of fruiting shrubs like currants, madrones and black-cap
raspberries. If you keep track of
volunteer plants, you may discover a prize, and can move it in the fall to your
preferred place.
Growing natives from cuttings
Cuttings, divisions, bulb scaling, layering are all examples of vegetative propagation- the resulting plants will all be genetically identical to the plant from which the pieces were taken. There are plants that typically produce large “clones” in nature, by spreading via stolons or suckers (Strawberry, Salal, Red Osier Dogwood, Nootka Rose, Willows). Though the plants may appear to be separate individuals and may in time in fact break off from connections with the mother plant, they are genetically identical and all constitute in effect a single genetic individual.
Cuttings, divisions, bulb scaling, layering are all examples of vegetative propagation- the resulting plants will all be genetically identical to the plant from which the pieces were taken. There are plants that typically produce large “clones” in nature, by spreading via stolons or suckers (Strawberry, Salal, Red Osier Dogwood, Nootka Rose, Willows). Though the plants may appear to be separate individuals and may in time in fact break off from connections with the mother plant, they are genetically identical and all constitute in effect a single genetic individual.
When you purchase plants of
a named cultivar from a nursery, particularly if it possesses an unusual trait
like variegation resulting from a somatic mutation, all such plants are likely
to have been produced vegetatively through cuttings or tissue culture.
Many plants, including many
natives, are easy to grow from cuttings.
This can be done without harming the “mother” plants; it can even be
incorporated into pruning or deadheading.
The plants you get will be genetically identical to the plants from which
the cuttings were taken. If you’re
hoping to produce several of one species, it might be advantageous to take
cuttings from different individuals (plants that came from different seeds
originally) or even different populations, so that you will have a little genetic diversity in your garden. This is particularly relevant if you
then hope to collect and propagate seeds from the resulting plants.
Choose plants with fairly
close internodes (vertical distances between true leaves, not leaflets, along the
stem). Cuttings are easiest from
perennials or shrubs with firm, solid stems, not hollow or latex-filled.
Cuttings will work best when
taken from the plant while it is actively growing but not flowering. If the
plant is in bloom, remove flowers from cuttings.
Cuttings in general are best
taken from younger plants, or from the younger portion of a large plant. Avoid
taking cuttings from plants that look unhealthy.
Auxins are
one of several classes of naturally-occurring hormones in all plants. To facilitate
rooting, you can dip the ends in rooting hormone (a synthetic form of the auxin
IAA) before planting. Experts
disagree about how important this is, and it may be more helpful for some
species than for others. Synthetic
hormones, available as liquid, gel or powder, have a shelf life of 18-24
months, so it is recommended that you buy no more than you can use, and date
the container. Use gloves when handling the chemicals, and take care to store
securely.
Another way
of applying auxin to cuttings is the use of willow water, made by simply
cooking willows, which are naturally high in auxin.
Wounding
the stem of a cutting can facilitate uptake of water and hormone, and may be
useful for more difficult to root spp.
Cut a section of the outer covering of the stem, or hand-strip lower
leaves. The wound also encourages formation of callus; in some cases, it makes
root emergence easier by removing thick woody tissue.
Callus is
an area of new cell division, with undifferentiated cells; roots may form more
easily here.
A good cutting should have
at least two bare nodes at the lower end (where roots can emerge) and one or
two leafy nodes at the upper end.
Several such cuttings may be possible along one shoot of a plant. Use a sharp knife to make clean cuts;
scissors cut by mashing, and are not recommended.
Roots will emerge from nodes
where leaves have been removed, when the nodes are submerged in water or soil.
This works because plants have meristematic tissue (undifferentiated cells,
similar to stem cells in humans) at nodes and tips.
Cuttings can be grown
outdoors in mild weather, or on a windowsill during cooler times of the
year. Indirect sunlight is best.
When you take cuttings will determine the care and
treatment of the plant material. It gets easier as the growing season moves
toward fall.
Softwood cuttings are taken in early spring during active growth (many
shrubs), and should bend but not
snap. These should ideally receive bottom heat (70 degrees) and a steadily
moist environment with good air circulation. Their tender tips are subject to
wilting if they dry out.
The best time for green or "semi-hardwood" cuttings (many shrubs and perennials) is in mid-summer, but
spring should be fine for many. As with softwood, the stem should be bendable
but not snap. Since the tissues are more mature, they do not need babying like
the softwood cuttings taken earlier. You can reduce evaporation rates by
cutting some leaves in half. Plant green cuttings in regular potting soil and
keep moist and fairly warm. Best light levels are moderate; direct sunlight is usually too strong. Most plants should root in a few weeks
(4-6 for most, less for willows).
Hardwood cuttings are taken in fall just after leaf fall, or
right before bud break in the early spring; treat with rooting hormone unless
you know the species to root easily (willows, dogwoods, shrubs that spread with
rhizomes) and plunge into medium (soil or sawdust etc.) in a container or
garden bed where they will not be disturbed until the next spring or fall.
Choose thick, healthy shoots from current season’s growth, 8-12” long, and
submerge most of the shoot in medium (soil, sawdust). The convention for
trimming cuttings is to cut square across the bottom, just below a node, and
use an angled cut at the top just above a bud. With extra-slow plants or where winters are harsh, cuttings
can be kept in a frost free garage or a cold frame.
A few very easy plants,
often with wiry, semi-woody stems, can be rooted in water. Most will be more successful in moist
soil, vermiculite, or soilless potting mix in small pots or deep
six-packs. For long cuttings, use
a deep pot to maximize the rooting zone.
Plant more cuttings than your target number of plants, assuming that you
will have some losses.
To check for progress, turn
the pot upside down carefully in your hand, the cutting between two fingers,
keeping the rooting medium in the shape of the pot, slide it out and check to
see if white, hairy roots have spread through the medium sufficiently to be
showing on the outside of the soil ball. If this has not occurred, carefully
replace the soil and cutting into the pot and wait another couple of weeks.
Some plants, like Castilleja (Indian Paintbrush) require complex relationships to other plants and
to microbes in the root zone; these are likely to be difficult to grow in
captivity.
However, there are some
stubborn horticultural myths about difficulty, as well. Trillium takes a very long time (8 years, under ideal
conditions) to mature from seed to bloom.
However, contrary to legend, it is fairly easy to transplant, and easy
to maintain in a pot or garden setting for many years. There is a horticultural legend that
Madrones are difficult or impossible to grow in cultivation. It simply isn’t true. Ease of germination can be deduced from
their habit of profligate self-seeding.
Disappointments with pot culture are likely due entirely to the same
thing that sometimes kills mature madrones in over-tended landscapes: water.
Once rooted, established young plants need very, very little of it.
Detailed protocols for
general propagation can be found in many books and on the internet. Some resources coming from academia can
be very useful for information about native species, time to germination, etc.
but a caveat is in order. Many of
these resources give instructions that are very complicated and suggest that a
high level of precision is needed for germination success.
Experienced growers will
tell you that with simple pretreatments where needed, fall sowing, and
reasonable attention to horticultural basics like watering etc. as outlined
above, many native plants are very easy to grow without need for a greenhouse,
specialized equipment, precise timetables, thermometers, fancy lights, etc.
Easy natives to grow
from cuttings:
Penstemon spp.
Lonicera spp.,
(Honeysuckle, Twinberry)
Ribes
sanguineum, (Red-flowering
Currant), other Ribes spp
Symphoricarpos
albus, (Snowberry)
Rubus
spectabilis, (Salmonberry)
Thuja plicata,
(Western Redcedar)
Physocarpus
capitatus, (Ninebark)
Oemlaria
cerasiformis, (Indian Plum)
Sambucus
racemosa, (Red Elderberry)
Philadelphus
lewisii, (Mock Orange)
Cornus sericea, (Redosier Dogwood)
Salix spp., (Willow)
Easy natives to grow
from seed
Graminoids: Grasses,
rushes and sedges: Festuca, Carex, etc.
Iris spp. (not Iris
tenax, which takes 2 years or
longer to germinate!)
Berberis (or: Mahonia, syn.) spp. (Oregon Grape)
Lonicera spp.
(Honeysuckle)
Asteraceae, including
Eriophyllum, Balsamorhiza, Aster, etc.
Collomia
grandiflora
Aquilegia spp. (Columbine)
Asclepias
speciosa, other spp. (Milkweed)
Sambucus spp., (Elderberry)
Lupinus spp*
Arbutus
menziesii (Madrone)
Camassia spp
Malvaceae, including Sidalcea spp. (Mallow)
Oenothera spp.
(Evening Primrose)
Clarkia amoena, other spp. (Godetia)
Epilobium
angustifolium (Fireweed)
Lewisia spp. (Bitterroot)
Lomatium spp.
Ribes spp. (Currant)
Sorbus spp., (Mountain Ash)
Acer spp., (Maple)
Seed Germination
Basics
1. Pretreatment
A. Scarification or soaking
B. Vernalization or
stratification
2. Planting
A. Not too deep!
B. Potting soil or
seed-starting mix
3. Protection from
birds and bugs
4. Frequent, gentle
watering
5. Strong, direct
light
Cutting basics
1.
Plant
choice: solid, green stems are easiest
2.
Best
time: spring to mid-summer
3.
Ideally:
2 nodes for rooting, 2-3 small leaves, no flowers
4.
Rooting
hormone
5.
Well-drained,
consistently moist media
6.
Indirect
light, warmth