Forays in Propagating Native Bulbs and Corms from Seed

By Nancy Gilbert, Redbud Horticulture Co-Chair

Hartweg’s Iris (Iris hartwegii)

To propagate any native geophyte from seed, you first need a good source of viable seeds. Collecting native bulbs and corms from the wild is illegal, as bulb poaching poses a serious threat to our native bulb populations.

You can order native bulb and corm seed from online suppliers, but, if you want to grow a local ecotype, you’ll have to collect from local seed sources. You can collect seed on your own property. To collect on public lands, you need a permit; for private lands, you need landowner permission. You can also collect along county roadway easements in remote areas.

Wherever you collect, do so responsibly: Take no more than about two percent of a large stand of a species, and never collect in consecutive years after a poor crop.

Stratify Seeds

The purpose of stratification is to mimic nature, which means most native bulb and corm seeds need a period of either cold or warm moist conditions, or a combination. Cold stratify seeds in moist paper towels or moist vermiculite/peat moss mix inside plastic bags in the fridge.

Or do it the easy way ­— just locate your flats of seeds in a safe outdoor location and let Mother Nature stratify them. Most local seeds do fine in our local conditions if you seed them in flats in the late fall or early winter; they will go through our rain/freeze/thaw winter cycles.

Lily species are unusual in that they require a period of warm stratification followed by several months of cold stratification, so seed them in early fall.

Plant Seeds

Plant seeds in October and November. For seeding in pots and flats, use a mix of 1 part sphagnum peat moss, 1 part medium grade perlite, and 1 part vermiculite. To prevent disease, use only clean and sanitized pots and flats . I recommend standard 17-inch square, plastic propagation flats with mesh bottoms. Line the bottom with landscape fabric or cardboard to keep seed mix and roots in the flat. Fill the flat about two-thirds full; then gently tamp to firm up the mix.

Spread the seed thinly and evenly over the flat; you may mix the seed with clean, dry sand to help with this.

Cover seeds with 1/8-inch (smaller seed) to ¼-inch (larger seed such as lilies) and tamp down again. You may add a fine layer of pine needle mulch to reduce washing out. Set an upside-down mesh flat or aviary wire on top to protect from digging by rodents, etc. Then gently and thoroughly water in with a mist-type water spray. Try to locate the flats off the ground on a bench or weather-resistant table in a part-shade location.

Label seed pots and flats with species name and seeding date!

Water Flats to Mimic Traditional Rainy Season

After seeding, keep moist until rains take over. If we have dry periods in winter, mist to keep flats moist. Stop watering all dryland bulbs and corms when the weather warms, as high temperatures and moisture cause bulbs to rot from soil pathogens. A few bulbs, such as tiger lily (Lilium pardalinum), are wetland species that need moisture year around.


Three-year-old Calochortus bulbs in deep flat for growing on. Cover is a turned over 17” plastic flat to keep out most rodents.

Once small, grass-like seedlings emerge the first year, you may do a topdress (sprinkling on top) fertilizing of your bulbs. The second year, you may topdress fertilize in late fall to early winter. Never use manure-based composts to fertilize native bulbs, as this promotes soil-borne diseases.

I use a commercial organic fertilizer, such as from Dr. Earth or Espoma, or a slow-release fertilizer such as Osmocote bulb blend, which contains the organic compound IBDU. In early spring, you may include a liquid fertilization at half strength. Tomato fertilizer formulations work well for bulbs, which like that extra potassium and lower nitrogen.

Harvest and Store Bulbs

During summers, store bulb flats, pots and bins in a cool, dry location over the summer and protect them from predation by rodents. You could place them on a bench on the north side of a building, spread 90-percent shade fabric over them, or even place flats on a shelf in a cool area indoors.

Time to Plant Your Bulbs!

Dipterostemon capitatus corms with small offset cormlets. These little offset cormlets are about the same size as 2-year-old corms would be from seed.

Growing most bulbs or corms from seed to flowering size may take two to five years. Homeowners usually find it easiest to harvest them after two years in the flat, as they’ll need repotting anyway into a new and different type of pot and potting mix.

By July, your flats or pots will be very dry, and the bulbs will be dormant. Harvest between August and early October, before the rainy season starts. I usually harvest in September. To harvest, gently turn the flat or pot upside down onto a roomy, clean tabletop. (You may want to place cardboard over the flat before tipping it.) Remove the flat and landscape fabric/cardboard, and spread out the mix.

At this stage, bulbs and corms will be quite small, so wear your strong glasses and go slowly! Now the search begins for those little corms or bulbs. Once you think you have found them all, you may dispose of the seed mix; as you may have missed a few bulbs, dump that seed mix in your garden so that any escapees might grow on.

You may plant the bulbs or corms out in the landscape immediately or wait a few weeks. To hold them for a few weeks, keep them in breathable bags or containers, and place in a cool, dry location until planting. Plant any lily bulbs immediately; because they have no bulb tunic to protect them, they dry out quickly.

Plant your dryland bulbs in a garden location that receives no summer water and is similar to their wild habitat conditions. Lilies are a favorite of deer, so either plant them inside a cage or fenced area of your garden, or plant them where they can grow up through a native shrub and be less obvious.

white pendulous flower with bit of light pink at base of petals
Calochortus albus flowering in Nancy’s garden

Once established, most native corms and bulbs are carefree. They give us, and pollinators, joy for many years, while slowly spreading about the garden by seed and/or bulb offsets.

Resources Specifically About Propagating Native Bulbs

The Pacific Bulb Society (PBS)

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