The world’s population is rising at an exponential rate (7.6 billion and counting), and because all of those people need someplace to live, the amount of wild land is shrinking even as I type this sentence.

That in a nutshell, or seed pod (pun definitely intended), is why gardeners should include more native plants in their domesticated gardens, Heather McCargo of the Portland-based Wild Seed Project said in a recent talk at the Thomas Memorial Library in Cape Elizabeth.

“Plants are the base, the beginning, of the food web,” she said. “When something is removed from nature, the ecosystem changes. Fifty years ago there was twice as much nature as there is now.”

The ecosystem includes birds, animals and insects as well as the plants that evolved along with them. The native wildlife needs the native plants for food and shelter, and the plants need the wildlife for pollination and, in many cases, in order to spread their seeds.

Not just any native plant will do. As an example, McCargo discussed echinacea, or purple coneflower, a prairie native that does well in Maine gardens. Butterflies love it, a fact I can attest to: In our garden, when the coneflowers bloom in mid- to late-summer, they are usually covered with butterflies.

But many of the echinaceas sold in nurseries are hybrids, often with double flowers that, because the stamens are replaced by petals, are sterile and lack the nectar and pollen that feed insects. These plants offer no benefit to wildlife.

New England asters

Or consider New England asters, a wonderful, late-blooming plant that is essential to supporting bees and other pollinators at a time of year when few other plants are in bloom. When I was cutting some recently to bring inside, I had to search hard to find stems that weren’t coated with bees.

Asters can grow 5 feet tall, but many people grow shorter hybrids such as “Purple Dome,” which aren’t as helpful for the environment. If you’re a gardener who prefers the shorter asters, McCargo suggested cutting back the wild versions earlier in the season rather than growing the hybrids.

Since the plants people should grow to help the ecosystem are freely available in the wild, you might think that the simplest way to get them would be to go out into the woods or meadows, dig up a few and plop them into your garden. Don’t! McCargo said that just removes healthy plants growing in the wild.

“It’s not really good to transplant them,” she said. “Propagation from seed is the only way to increase the population.”

In addition, growing from seed produces more genetic diversification, which has a couple of advantages. First, it gives you plants with varied looks. More importantly, diversity makes it much more likely that some of the plants will survive tough times, such as droughts, floods and warmer temperatures as a result of climate change.

The most important step to seed collecting and saving is to let the seeds develop completely, McCargo said. Gardeners and state crews mowing on the side of roads often cut the wildflowers down shortly after they blossom, before the seeds have had time to develop. When mowing a meadow or cutting back a garden, do it as late as possible.

Some wildflower seeds can be stored dry; others will not sprout if they dry out. For the ones that must stay moist – including viburnums, native dogwoods and trilliums – she suggests waiting until they get fully ripe, putting them in a plastic bag, squishing them and letting them ferment. Once that process is complete, plant them immediately.

Cardinal flower

Seeds that can dry out are more plentiful, including all the milkweeds, cranesbill, blue flag iris, asters, goldenrod, cardinal flower and rudbeckia.

But saving seed is not that important for home gardeners, at least not right away.

“Seed collecting is the second step,” McCargo said. “They should sow the seed first.” She recommends buying seed, sowing it and developing lots of wildflowers. After you have a lot of native wildflowers on your property, then you can get into the more complicated process of collecting seed.

Swamp milkweed attracts butterflies.

Most wildflower seeds need a winter of cold weather before they will sprout. Even those that don’t will do better if they have a cold period, McCargo said, so late fall, usually after Thanksgiving, is the ideal time to plant. She often does her planting on New Year’s Day.

And although many people think they can get wildflowers simply by scattering the seed, they’re mistaken. Collecting seed is a lot of work, and scattering them is inefficient and wasteful – planted that way, just a tiny percentage of the precious seeds will ever grow.

While creating a raised nursery bed outside will work to grow the seeds, McCargo prefers a different method. She plants in square 4- to 6-inch pots, which she fills with a good compost-based potting soil that has all the natural organisms that help the plant grow.

She spreads the seeds thickly on top of the soil. (Keep in mind that different species will sprout at different times.) She covers the seeds with sand, which allows enough light through to let the seeds germinate and at the same time prevents weed seeds from sneaking in. The sand should be about the same depth as the seed’s diameter.

She takes the pots to a protected area outdoors, covers them with rabbit wire – a metal mesh with holes a quarter- to a half-inch square – and leaves them until spring.

In spring, you can take a shovel and plant the entire pot in your garden, McCargo said, but you may have better success if you transplant the wildflowers into larger pots, let them continue to grow in the pots over the summer and only in the fall plant them in the garden.

When it all succeeds, your backyard can replace at least a little bit of the wilderness we are so rapidly losing.

Tom Atwell is a freelance writer gardening in Cape Elizabeth. He can be contacted at 767-2297 or at: tomatwell@me.com.