When and How to Plant Native Plants in Chicagoland

Native Plants in Chicagoland · Part 3 of 7

We've covered why native plants matter and what not to plant. Now the practical part: when to plant, whether to start from seed or plants, how to clear a spot without chemicals, and how to get a new planting through its first year.

The short version: native plants are easy to grow, but they work on a different calendar than annuals and lawn. Fall and winter, not spring, are some of the best times to get started.

Know your zone (and why it matters less than you'd think)

The USDA updated its plant hardiness zone map in 2023. Most of Chicago is now in zone 6a, with a warmer 6b strip along the lakefront and colder 5b pockets in the outer suburbs.

For native plants, the zone is mostly a non-issue. Plants native to northeastern Illinois have survived far colder winters than anything on the current map. The zone matters more when someone tries to sell you a plant from farther south "because Chicago is warmer now." Those can still get caught by a bad January.

The native planting calendar

A few woody plants, including redbud, flowering dogwood and magnolia, are often recommended for spring planting instead of fall.

Why fall is underrated

Spring feels like planting season, but plants put in during spring go straight into a Chicago summer with shallow roots. Plants put in during early fall get weeks of warm soil and cool air to grow roots without the stress of heat, then a full spring to settle in before their first summer.

Trees and shrubs get an even longer runway. Their roots keep growing after the leaves drop, right up until the ground freezes, which in our area can be as late as January or February. Late fall is also when nurseries discount the stock they don't want to carry over winter.

Seeds, plugs or potted plants?

For most Chicago yards, plugs are the sweet spot. They're cheap enough to plant densely, small enough to establish quickly, and you know exactly what you're getting. Planting them close together, roughly a foot apart for most perennials, helps them fill in fast and crowd out weeds.

Starting from seed: let winter do the work

Many native seeds won't sprout until they've been through a cold, damp winter. It's a survival trick: it keeps them from germinating in a warm October and getting killed by frost. Gardeners call this cold stratification, and the simplest way to provide it is to sow outdoors in late fall or winter and let the weather handle it.

Dormant seeding

Scatter seed directly on prepared, bare soil any time from late October through March, after a hard frost. Press it in lightly by walking over it; don't bury it deep. Sowing right before or onto a light snow works well, since melting snow helps work the seed into the soil. Expect germination in spring, with some species waiting until the following year.

Winter sowing in milk jugs

If you'd rather grow your own plugs, winter sowing turns recycled containers into mini greenhouses:

1. Cut a clean gallon milk or water jug most of the way around, a few inches from the bottom, leaving a hinge.
2. Poke drainage holes in the bottom and fill with a few inches of moist potting mix.
3. Sow seeds on top, label the jug, tape it closed and leave the cap off.
4. Set it outside in a spot that gets sun and snow. A porch, deck or back steps work fine.
5. In spring, open the jugs on warm days, then transplant seedlings once they have a few sets of true leaves.

December through February is the usual window. Good beginner species include wild bergamot, black-eyed Susan, purple coneflower, anise hyssop, columbine and common milkweed. Native seed suppliers usually print germination instructions on each packet; follow those when they differ from the general method.

Preparing the site

Site prep matters more than anything else you do, especially for seed. Native seedlings are slow and small at first, and they can't compete with established lawn or weeds. You have several options:

• Sheet mulching (best for most yards): mow the lawn short, cover it with overlapping plain cardboard (tape and labels removed), soak it, and top it with several inches of shredded leaves or wood mulch. You can plant plugs right through it by cutting an X in the cardboard. Done in fall, it's ready for spring planting.
• Smothering with a tarp: pin a dark tarp over the area for several weeks in warm weather to kill the grass underneath. Faster than cardboard, but it looks like a construction site while it works.
• Cutting the sod: for small areas, slice off the turf with a flat spade or a rented sod cutter. Quick results, but hard work, and you have to do something with the sod.
• Skip the tiller: tilling brings buried weed seeds to the surface, where they sprout faster than your natives. If you're seeding, disturb the soil as little as possible.

Before you dig anything, especially a hole for a tree or shrub, contact 811 to have underground utilities marked. It's free, and it's required in Illinois before excavating.

Working with Chicago clay

Much of the Chicago area sits on heavy clay, and city lots often have a layer of construction fill on top. The good news is that many prairie and savanna plants evolved in exactly this kind of soil.

• Pick plants for the soil you have. Plenty of natives like clay: New England aster, prairie dropseed, swamp milkweed, blue flag iris, golden alexanders, switchgrass and most goldenrods.
• Skip heavy amending. Most natives don't need rich soil, and too much compost or fertilizer makes many prairie plants grow tall and flop over. Never add sand to clay; it can set up like concrete.
• Don't work wet clay. Digging or walking on soggy clay compacts it. Wait until a handful crumbles instead of forming a ball.
• Let roots do the work. Over a few seasons, native roots open up compacted soil better than any amendment.

Planting day

• Water plants in their pots an hour or so before planting.
• Loosen circling roots gently with your fingers before setting plants in the ground.
• Plant at the same depth the plant was growing in its pot. For trees, keep the root flare (where the trunk widens at the base) at or slightly above ground level, and dig the hole two to three times as wide as the root ball but no deeper.
• Water deeply right after planting.
• Mulch lightly: an inch or two of shredded leaves or wood mulch, kept off the plant crowns and tree trunks. Skip mulch in areas you've seeded.
• Skip the fertilizer. Natives don't need it, and new plants especially shouldn't be pushed into growth.

The first year: sleep, creep, leap

As we mentioned in Part 1, native perennials famously "sleep" the first year, "creep" the second and "leap" the third. Most of the growth in year one is underground. A planting that looks sparse in its first summer is usually right on schedule.

• Watering: water deeply about once a week during dry spells in the first season, more in a heat wave. Fall plantings and new trees should be watered until the ground freezes. Most natives can be weaned off by year two; trees can take longer.
• Weeding: this is the real work of year one. Weed regularly so your natives aren't shaded out.
• Learn your seedlings: if you seeded, many young natives look like weeds at first. When in doubt, leave it until you can identify it.
• Mow seeded areas high: in a seeded meadow, mowing to about 6 to 8 inches a few times during the first summer knocks back fast-growing annual weeds without hurting the slower native seedlings below.

By the third season, a well-planted native bed mostly takes care of itself: the plants shade out weeds, survive dry spells without help, and fill in the gaps.

Sources

• Illinois State Climatologist, New USDA Plant Hardiness Zones Map
• WTTW, USDA's New Plant Hardiness Map Puts Chicago in Warmer Company
• University of Illinois Extension, Plant native perennials in the fall for healthy spring growth
• University of Illinois Extension, Planting trees in fall brings benefits spring doesn't afford
• Prairie Moon Nursery, Planting Instructions for Hand Sowing Your Native Seed Mix
• University of Illinois Extension, How to try winter sowing