How to Grow Aster
Aster At a Glance
Difficulty
Moderate
Category
Flower
Sun Exposure
Full Sun, Partial Sun
Frost Tolerance
Frost Hardy
Cold Hardiness
Survives to -34°C
Plant Family
Asteraceae
Growing Season
Cool Season
Plant Lifecycle
Perennial
How to Start It
★ Recommended for beginners
Aster seeds need a cold spell before they sprout, so the easy way is to sow them outdoors in late fall and let winter do the work. Press the seeds onto the soil and cover them very lightly, about 0.5 cm deep, in a pot or a marked spot of the bed. They sprout in spring, usually in 7 to 14 days once the soil warms: thin them to 30 cm apart. For a spring sowing instead, mix the seeds with damp sand in a bag and keep it in the fridge for 4 weeks first.
Garden asters, including the native New England aster, light up fall with starry daisy flowers just when bees and butterflies need food most. They are long-lived and come back every year, and plants from seed usually flower fully from their second year. Old clumps get crowded and woody in the middle, so splitting them every 2 to 3 years keeps them blooming.
When To Start
First chance to plant
7 Days After Last Frost
Last chance to plant
30 Days Before First Frost
When should you plant Aster?
Your planting dates depend on your local climate. Sign up and add your location to unlock personalized dates.
Your Aster Planting Window
Start planting
May 15, 2026
Last chance
Sep 10, 2026
Your Aster Calendar
Set your location to turn these into exact dates and reminders.
Sow aster seeds outdoors now, winter will wake them
2 weeks after your first frost· every year
Plant or divide asters in spring, every 2 to 3 years
Around your last frost· every year· optional
Cut asters for the vase and enjoy the fall flowers
45 days before your first frost· every year· optional
Did you water your aster seedlings today? Keep the top of the soil damp until they are up and growing.
About 1 days after you plant it
Your aster is growing nicely! Water at the base and give it good airflow to keep the leaves healthy.
About 44 days after you plant it
Your aster is heading toward bloom. Cut a few flowers once they open and more will follow.
About 74 days after you plant it
Picking time may be here: check your aster.
About 90 days after you plant it
The Journey Ahead
Aster's Lifecycle
Seedling
Mature Plant
Seed Production
Step 2
Planting & Sprouting
Expect sprouts in 7–14 days
Growing Tips
- 1Plant asters in full sun, at least 6 hours a day, for strong stems and lots of flowers.
- 2Mix some compost into the soil at planting time, then a thin layer each spring is enough.
- 3Water deeply during dry spells, at the base and not on the leaves, since thirsty plants get powdery mildew (a white dust on the leaves).
- 4Skip extra feeding, because rich food makes tall, floppy stems.
- 5In early summer, cut the stems back by about a third so the plants grow bushier and do not flop.
- 6Space plants about 30 cm apart and thin crowded stems in spring so air flows through and keeps mildew away.
Seedling Phase
Step 3
Growth & Maturity
~90
Days to Maturity
60 cm
Mature Height
60 cm
Mature Width
Pests to Watch For
Diseases to Watch For
Mature Plant
Step 4
Harvesting
Harvest Window
30 days
When to Pick
Cut flowers at peak bloom
How to Harvest
- 1Cut stems for a vase when about half the flowers on a stem are open.
- 2Strip the lower leaves and put the stems straight into water, where they last about a week.
- 3After flowering, you can leave the stems standing over winter, since the seed heads feed birds and the hollow stems shelter helpful insects.
- 4Cut the old stems down to the ground in early spring, before new shoots appear.
- 5Every 2 to 3 years, dig up and divide the clump in spring to keep it healthy.
Step 5
Saving Seeds
How to Save Seeds
Garden asters are often named varieties that do not come true from seed, and different asters cross through bees, so seedlings may look different from the parent. Wild asters like New England aster come close to true. Let the flower heads dry on the plant until they turn fluffy like a small dandelion, then pick them on a dry day. Rub the heads between your fingers over a bowl to free the tiny seeds, and let them dry a few more days. Store them labelled in a cool, dark, dry place and sow them the next fall, while they are fresh.
Seed Production
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