Propagating native plants

It’s surprisingly hard to find many PNW native plants in nurseries in this region.  You  may find that the easiest and least expensive way to obtain many 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.

Growing natives from cuttings

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.  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.

Cuttings can be grown outdoors in mild weather, or on a sunny windowsill during cooler times of the year.  Without a greenhouse, probably the best times to start cuttings are late winter through mid-summer, so that once plants develop good roots there will be time to get them established outdoors before the weather turns cold.  The best time for green or “softwood” cuttings is in mid-summer, but spring should be fine for many.  Semi-hardwood cuttings are taken in late summer, and hardwood cuttings in fall; these take longest to root, and are not recommended for beginners.

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.  Plant more cuttings than your target number of plants, assuming that you will have some losses.  To facilitate rooting, you can dip the ends in rooting hormone before planting (experts disagree about how important this is, and it may be more helpful for some species than for others).  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; you can test progress by occasionally tugging very gently on the shoots. 

Growing natives from seed

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. Seeds can be stored under cool, dry conditions, and most will last several years; a few species need to be planted very soon after ripening (e.g. Trillium and possibly Delphinium). 

Many seeds, including most natives, benefit from pretreatment.  Most commonly for PNW plants, this will include at minimum several weeks of exposure to cold, termed stratification or vernalization.  Stratification is a method of storing seeds dry in the freezer or (preferably) moist in the refrigerator, often in moist peat 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.

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, 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 seeds can be planted in good quality potting soil, or a mixture of potting soil and seed starting mix.  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. 

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 rain water 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 germinate 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.

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. 

If you have the time and the space, a seed-starting setup may be particularly helpful beginning in spring, for germinating seeds and growing young seedlings.  A simple setup that will accommodate 4 standard 1 ft x 2 ft flats requires three 4-ft long fluorescent fixtures with two bulbs each; total cost can be under $100, including lights, framing materials and hardware. 

Plans can be found on the web (e.g. http://davesgarden.com/guides/articles/view/464)

More expensive, full-spectrum “grow lights” have not been found by most growers to confer noticeable advantage over standard fluorescents. If you use such a setup, it’s important to keep lights on 10-14 hours a day, and keep the bulbs as close to the tops of the tallest seedlings as possible without having the leaves touch the lights.

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.

When growing seedlings indoors, ventilation and air movement are important to discourage fungi and some insect pests.  For greenhouses, simply opening a door will prevent “cooking” your plants on a warm day, and help provide air movement.  A small clip-on fan can be helpful for the home grower.  Another advantage to air movement is that it facilitates thigmomorphogenesis, a nifty term that means that young shoots grow thicker and stronger when they are vibrated a little.  To this end, some propagators gently tickle all their seedlings daily.  No, really.  (Saying gitchy-goo is optional.)

Overall, larger seeds, harder seeds, or those enclosed in berries tend to be easiest to germinate.  On the other hand, the seeds of some species, notably some lily family seeds (e.g. Lilium, Trillium, Calochortus), have a very complex germination history that takes two years to commence, and several more years to produce a mature plant. These are not recommended for novices. Note that not ALL Liliaceae are difficult- some with stony seeds- Camas, Brodiaea, etc.- are quite easy.

Lupines (which have hard pea- or lentil-like seeds that are quite toxic) are easy to germinate even with seeds several years old, but established plants deeply resent life in a pot.  Specialized rhizobia (inoculants of beneficial root-associated bacteria, such as garden centers often sell for peas, which are in the same family) are available but not crucial.  Start seedlings in six packs or plug trays and transplant carefully to 4” pots, then to the ground as soon as practicable.

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.  Specific protocols for native plants can be found as well, notably in Propagation of Pacific Northwest Native Plants.by Rose, Chachulski and Haase (Oregon State University Press, 1998).  This book and other 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 (other than Rose et al) give instructions that are very complicated and suggest that a high level of precision is needed for germination success.  I believe that these protocols are generated exclusively in academic contexts, and have more to do with conventions of scientific research than with horticultural reality.

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.

A very useful page giving general instructions for seed collection, storage, pretreatment, and planting is: http://gardening.wsu.edu/text/nvgrowng.htm

In my small nursery at Island Horticultural Services, I offer many of the plants listed here. I sell at Poulsbo Farmers' Market, and from home by appointment.  As a landscaper and botanist, I offer professional design, installation and consulting services, which may include an emphasis on native plants.

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