Propagating native plants from seeds protects genetic diversity and is simple to do. To discuss all the benefits and the steps for the easiest way to start and grow native seeds in winter (no special equipment required) is my guest this week, Heather McCargo, the executive director of the Wild Seed Project.
Heather now lives in Maine on an old farm where she has restored meadows with native plants, and she grew up in Western Pennsylvania, outside of Pittsburgh. Her mother was a long-time organic gardener and naturalist. Heather spent her time outdoors playing in the woods, fields, wetlands and streamsides. “I’m a child of nature,” she says. She studied plant ecology in college and did several horticultural internships, getting hands-on experience.
Heather had the opportunity to apprentice under Jack Alexander, the propagator at the Arnold Arboretum of Harvard University in Boston. Jack was growing hardy woody plants from around the world and taught Heather the many methods used to encourage seeds to germinate: filing the seed coat, putting a lit match to the seed, pouring boiling water on the seed, putting the seed in a refrigerator, etc. Though all these methods have some degree of effectiveness, Jack taught Heather in her first week that the simplest, most effective method of all is to just throw the seeds outside.
Heather says her goal is not to save native seeds but to sow native seeds and make more plants. She acknowledges that there are native seeds that are difficult to start and slow to grow but says many others are easy. From a little pot with 30 to 100 native seeds, you can plant out a population of natives. It’s economical and rewarding, she says. “If you are always giving your neighbors giant zucchinis, instead you could be sharing those plants with your friends.”
Heather says she started the Wild Seed Project, a nonprofit organization, because the work of collecting, cleaning and processing wild seeds is very time consuming and not economical. It requires a team of volunteers, though she says the work is, conveniently, a lot of fun.
Native Seeds & Plants Are Just Easier to Work With
In the 1990s, Heather worked as the propagator at Garden in the Woods, a 45-acre botanical garden in Framingham, Massachusetts, operated by the Native Plant Trust. When she stepped into the job, the garden was already engaging in outdoor propagation. “It’s so much simpler and a lot of ways, and you can do it,” she says.
When Heather turned her focus to propagating native species, she endeavored to mimic natural, outdoor germination. She finds that sowing native seeds is a lot easier than raising domesticated and cultivated plants, which require compost, manure and weeding to thrive. Native plants are adapted to our native soils so they don’t need all of the extra fertility that cultivated plants do.
Native seeds, unlike vegetable seeds, don’t want to be sown in your house under lights or in a greenhouse. They don’t want to be sown outdoors in late spring either. They germinate best when they are sown outdoors in late fall.
Native plants have their soil requirements — some like dry, sandy, gravelly soil, some like hot, baking clay, and others prefer wet or medium moisture soil — but they are overall less fussy.
The beauty of native plants is they are much more resilient and vigorous, Heather says. They never require compost and manure for extra nutrients. At most, for a slow-growing native that spends a long time in a pot, Heather will apply a weak seaweed solution fertilizer. For established plants, Heather rakes up her fall leaves and puts them on the planting beds. The leaves provide all the supplemental nutrients the natives receive.
Sow Native Seeds in Pots for Greater Success
Heather says she tells fellow gardeners in New England that seed sowing is an activity for over the winter holidays, when other outdoor gardening jobs are finished. In warmer climates, the timetable may be different but the plan of action is the same. Rather than just tossing seeds out into the landscape, sow them in pots. This greatly increases the seeds’ chance of germinating and growing into adult plants.
“Everybody wants to just toss the seeds out into the landscape, but what that doesn’t take into account is the dangerous life of a seed,” Heather says. “Most seeds that a wild plant produces don’t land in a place where they germinate and become an adult plant. A typical plant can produce millions of seeds over its lifetime, and those aren’t all becoming new plants. They get eaten by birds or mice. They become part of the food chain.”
But when a small pinch of native seeds is sown in little pots and put outdoors, almost all of the seeds will germinate. Clay pots work best because they are porous. Recycled plastic pots will also do the job but they hold water and don’t breathe. Fiber pots that are designed to decompose are not a good choice because the plants grow slowly.
Preserving Genetic Diversity
The native plant movement was progressing slowly in Maine. Heather thinks planting native was not a big concern in the state because it has a lot of wildland. But even in natural areas, the native plants are retreating.
Heather says seed sowing was a missing link. Nurseries are so focused on cloning, which means they propagate genetically identical plants by rooting cuttings. They breed native plants and deem certain selections to be superior, but while those selections may look nicer to us, they are often not superior in providing ecosystem services to the insects, birds and other creatures that depend on them.
For example, breeders may select plants with purple and red foliage because consumers find it attractive. But, Heather points out, purple and red repel our native Lepidoptera — our butterflies and moths. And plants selected for bigger flowers or double flowers are often sexually dysfunctional, which means they provide no nectar, pollen and seed.
“The biggest problem I have with cultivars is that they’re all cloned,” Heather says. “So we’re mass-producing a really narrowed gene pool.”
Just like the movement to bring back heirloom vegetables is designed to bring back the genetic diversity of our cultivated crops, the native seed movement is designed to broaden the genetic diversity of our native plants. Seeds are the result of two or more individual plants getting cross-pollinated, so each seed is a unique individual. The genetics are the raw material that allow plants to adapt.
When you sow seeds of a straight species of a native plant, that’s where the genetic diversity is. A cultivar of a native plant is often a clone with countless genetically identical siblings created from cuttings, divisions or other methods of clonal propagation.
Starting Native Seeds
Heather starts seeds outdoors in a compost-based potting soil. She sows one species per pot, leaving an eighth-inch of space between seeds. She then covers the seeds with coarse builder’s sand. The sand layer is as thick as the seeds are large. So an acorn would be covered by an inch of sand, and a sunflower would be covered by a quarter-inch. Tiny, dust-like seeds that are traditionally sown directly on the soil surface get just a little sand, like how much salt you’d shake on food.
The coarse sand protects the seeds from bouncing out of the pot in the rain. A storm window can be placed over the pots to protect the seeds from torrential rains, but the windows need to be removed as soon as the seeds germinate. If practicing the winter sowing method with milk jugs, the jugs will protect seeds from splashing out, but you also need to be careful that the plants don’t cook in the jugs in spring when the weather warms.
Because the pots are outdoors, Heather doesn’t combat fungus gnats, damping off, mold, mildew and other challenges that indoor seed starting poses. She never worries about the seeds rotting in wet weather either. The seeds can take it. However, being outdoors means the pots need protection from squirrels and chipmunks. Place a wire mesh over the pots to keep wildlife from digging.
Place the pots in a shady spot on an even surface, such as a stone terrace on the north side of your house. An even surface is important so the seeds don’t all shift to one side of the pot. The shade is important because, come spring, the seedlings will be at risk of drying out. All it takes is one hot day. When the seedlings are more established, a sun-loving species can be moved to a sunny spot.
Over the winter, the seeds may experience freezing rain, snow and sleet. That’s great because the seeds need fluctuation in temperatures to germinate. That freeze and thaw breaks apart the seed coat. If the seeds prematurely germinate during a warm spell, the plants are not doomed. The seeds really do know what they are doing, and the seedlings will just stay tiny until spring comes.
Potting Up & Planting
When summer comes, Heather moves plants from the small pot they started in, into a larger pot. The plants can be divided, but that causes root disturbance and slows the growth. If the plants really are too crowded, divide the contents of the pot into quarters, and put each quarter into a separate, larger pot.
Water the pots regularly throughout summer so they never dry out. Check three times a week for moisture and remove any weeds too. In September or when the heat of summer is over, plant the seedlings out into the landscape.
What It Means When Some Pots Have No Germination
Some species may germinate over the winter, some will germinate that first spring and others won’t germinate until the second spring after they were sown. Slow-growing lilies, Solomon’s seal, Trillium and wild ginger all need two springs.
If you sowed rather late, it could be that the seeds did not experience enough of a winter cold period. Another common problem is pots that dry out mid-germination. It could also be that the seeds were sown too deeply and did not get adequate light to germinate. You can give pots another year to see if the seeds will finally germinate. In fact, Heather has dumped out unsuccessful pots only to have the seeds germinate years later where she dumped them.
Wild seeds don’t like to put all their eggs in one basket. Some may germinate in the first year while other seeds of the same species will take longer. For example, only a third of the seeds of wild Geranium (Geranium maculatum) typically germinate in the first year. Heather pots up the seedlings and in the second year the remainder of the seeds germinate.
Pot Sowing Vs. Other Native Seed Starting Methods
There are other tried and true methods for starting native seeds outdoors. One is winter sowing and another is to broadcast sow seeds or use plugs to create a meadow, which was the subject of last week’s podcast.
Heather prefers starting seeds in pots because less seed is required. Pounds and pounds of seed are needed for broadcast sowing, and many of the seeds will be eaten by wildlife or fail to germinate for other reasons. Because the Wild Seed Project puts in the work to hand collect, clean and package seed, they want as many of the seeds as possible to become plants.
Though gardeners can start seeds in plug trays, Heather says that work is best left to the professionals because plug trays tend to dry out quickly if they are not frequently monitored and watered.
How to Tell When a Seed Is Ripe for Harvest
When harvesting native seeds, it’s important to correctly identify the species. It helps to survey plants while they are in bloom. That’s when it is easiest to get an accurate plant ID. And before taking any seeds from a plant, make sure that it is not a rare plant that is protected.
Aster seed heads get fluffy when the seeds are ripe. When you brush your hands on the seed heads, the seeds should come right off. If the seeds don’t come off, they need more ripening time. Drop the seeds right into a paper bag and give them a month in the bag to dry out before sowing them.
Milkweed pods change from green to tannish-gray and then start to split when the seeds are ripe. As the pods are starting to split, you can squeeze them, which will help them open along the seam. The seeds inside should be brown with long, silky appendages. You should separate the seeds from those silky appendages and allow the seeds to air dry.
Bee balm pods turn dry and grayish-tan. When you tip the pods over in your hand you’ll see tiny brown seeds come out. Again, let the seeds dry for a month in a paper bag.
Beardtongue (Penstemon) pods change from green to tan and waxy. When the pods go from waxy to woody and split a little at the top, they’re ready. In the wild, the pods shake all winter and disperse seeds.
Spring wildflowers and shrubs with fleshy fruit have much trickier germination needs and are not for beginners, Heather says.
I hope that after listening to my conversation with Heather McCargo you feel confident about growing native seeds. If you haven’t listened yet, you can do so now by clicking the Play button on the green bar near the top of this post.
Do you collect native seeds to propagate? Let us know in the comments below.
Links & Resources
Some product links in this guide are affiliate links. See full disclosure below.
joegardener Online Gardening Academy™: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.
joegardener Online Gardening Academy Master Pests, Diseases & Weeds: Learn the proactive steps to take to manage pests, diseases and weeds for a more successful garden with a lot less frustration. Just $47 for lifetime access!
joegardener Online Gardening Academy Perfect Soil Recipe Master Class: Learn how to create the perfect soil environment for thriving plants.
“Native Trees for Northeast Landscapes: A Wild Seed Project Guide” by Heather McCargo and Anna Fialkoff
“Native Plants for Roadside Restoration” by Heather McCargo
Arnold Arboretum of Harvard University
Disclosure: Some product links in this guide are affiliate links, which means we get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us, and compensation is not an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, Milorganite, Soil3, Exmark, Greenhouse Megastore, High Mowing Organic Seeds, Territorial Seed Company, Wild Alaskan Seafood Box and TerraThrive. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.