When to Plant Milkweed Seeds (By Climate, Not Calendar)

When to plant milkweed seeds depends less on the calendar and more on your winter. That is the honest answer, and it is also the useful one. A date that works perfectly in one state can be weeks off in the next, but the conditions milkweed seed is waiting for are the same everywhere: a stretch of cold, damp weather, followed by warming soil.

So instead of handing you dates, this guide sorts it by climate. Find your kind of winter, then follow the plan. We have already written about planting milkweed in the fall; this post zooms out to cover every season and all eight milkweeds we carry.

Why timing matters so much for milkweed

Most of our milkweed descriptions point to the same need: cold stratification, which is a stretch of cold, damp conditions that breaks a seed's dormancy. Until that happens, the seed stays put, no matter how nice the weather is.

You can meet that need two ways. Sow outdoors in fall or winter and let the weather do it. Or keep seed in the refrigerator in a damp medium for a set number of weeks, then sow in spring. Most of our milkweed descriptions give you exactly those two options. The right choice depends on what your winter looks like.

When to plant milkweed seeds in cold-winter regions

If your winters bring regular hard freezes, frozen ground, and snow, you have the easiest job of anyone. Gardeners searching "when to plant milkweed seeds in Michigan" or anywhere else with a real winter can follow this plan.

Best option: late fall

Sow after a few hard frosts, once the soil is cold enough that nothing wants to sprout, and before the ground freezes solid. Sowing earlier, into warm soil, risks seeds germinating right before winter, and tender seedlings may not survive it.

Also good: winter

Missed fall? Scatter seed onto bare soil, or even light snow, through late fall and winter. Freeze and thaw cycles will settle it into the surface for you.

Backup: spring, with the fridge

If you only got your seed in spring, give it a cold, damp spell in the refrigerator for the time its description recommends, then sow outdoors once the danger of frost has passed.

When to plant milkweed seeds in mild-winter regions

If your ground rarely freezes and winter is more cool than cold, outdoor sowing may not deliver a long enough cold spell for species that need it. You have two reasonable approaches.

• Sow in fall anyway, once it cools. Wait until the weather has turned cool for the season, then sow. Results will depend on how much real cold your winter brings.
• Stratify in the fridge, then sow. For more control, refrigerate seed in a damp medium for the recommended time and sow in late winter or early spring once the weather is settled.

Some milkweeds are a more natural fit for warmer places. Green Milkweed's description lists zones 6 to 10 and says it thrives in hot climates. Narrowleaf Milkweed's description lists zones 6 to 10 and can be direct sown in fall or early spring.

Milkweed timing, species by species

Here is what each of our milkweed descriptions says about when and how to sow.

• Common Milkweed (Asclepias syriaca): requires cold stratification for best germination. Plant in fall, or cold-treat seeds for 30 days before spring planting. Sow 1/4 inch deep.
• Swamp Milkweed (Asclepias incarnata): direct sow in fall, or cold stratify for 30 days before spring planting. Seeds need light to germinate, so barely cover them.
• Whorled Milkweed (Asclepias verticillata): direct sow in fall, or cold stratify for 30 days before spring planting. Barely cover the seed.
• Showy Milkweed (Asclepias speciosa): direct sow in fall, or cold stratify for 30 days before spring planting. Keep moisture consistent until seedlings are established.
• Prairie Milkweed (Asclepias sullivantii): sow in fall for natural cold stratification, or give it 4 to 6 weeks of cold, moist stratification before a spring sow. Sow about 1/8 inch deep and keep soil moist.
• Green Milkweed (Asclepias viridis): seeds benefit from cold stratification for best germination rates.
• Narrowleaf Milkweed (Asclepias fascicularis): direct sow in fall or early spring; seeds benefit from cold stratification.
• Butterfly Milkweed (Asclepias tuberosa): its description does not include sowing instructions, but it is part of our Fall Planting collection. Expect it to establish slowly.

Notice the pattern? Fall sowing fits nearly all of them, and for most, a spring sowing goes better after a cold spell first.

A simple seasonal plan

Fall

The main event in cold-winter regions. Clear the planting area of grass and weeds, wait for a few hard frosts, then sow at the depth the species calls for and press seed into firm contact with the soil.

Winter

Still open in cold regions: scatter onto bare soil or light snow. In mild regions, this is a good time to start refrigerator stratification so seed is ready for spring.

Spring

Sow stratified seed outdoors once frost danger has passed. Keep the soil evenly moist until seedlings are up, and keep weeds pulled while they are small.

Summer

Not a sowing season for milkweed. Use it to watch your young plants, note which spots stay wet or dry, and plan where next fall's seed will go.

Pick the right milkweed for your spot

Timing gets seed in the ground, but site gets plants to thrive. Swamp Milkweed prefers consistently moist soil and tolerates seasonal flooding. Common Milkweed is adaptable to most soil types and prefers well-draining ground. Whorled Milkweed is extremely drought tolerant and thrives in sandy, rocky soils. Match the plant to the place and your timing will pay off.

And remember why you are doing this. Milkweeds are the plants monarch caterpillars depend on. For more on building habitat that helps them, read How to Save the Monarch Butterfly. When you are ready to choose seed, our Butterfly Garden collection includes all of our milkweeds.

Quick answers

When should milkweed seeds be planted?

Late fall is best in cold-winter regions, after a few hard frosts and before the ground freezes. Otherwise, cold stratify seed in the refrigerator and sow in spring after frost danger passes.

When to plant milkweed seeds in Michigan?

In cold-winter places like Michigan, sow in late fall after a few hard frosts, or scatter seed onto bare soil or light snow through winter. Spring sowing works if you refrigerate the seed first.

Can I plant milkweed seeds in spring?

Yes, but most of our milkweed descriptions call for cold stratification first, typically 30 days in the refrigerator (4 to 6 weeks for Prairie Milkweed).

Can you plant milkweed seeds in summer?

Summer is not a good sowing time for milkweed. Wait for fall in cold regions, or stratify and sow the following spring.