Propagating native plants II

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 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.

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.

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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