Perennial asters, now classed as Symphyotrichum, are fall bloomers that feed late-season pollinators. University of Wisconsin Horticulture Extension notes species range from about 6 inches to 7 feet tall and grow in full sun or part shade. They are best planted in spring.
Aster at a glance
| Type | Flower |
|---|---|
| Season | Perennial |
| Sun | Full sun to part shade |
| Plant spacing | 24 in |
| Row spacing | 24 in |
| Per square foot | 1 |
| Seed depth | At surface |
| Days to maturity | Blooms late in the year, into fall |
| How to start | Plant in spring. |
| Water | 1 in per week |
These are the same numbers our plant spacing, square foot and harvest date calculators use. See every crop in the plant database.
When to plant aster
Plant in spring. Divide clumps every two or three years, in spring. Check your growing zone and frost dates.
How to plant aster
- Give full sun or part shade and moist, well-drained soil.
- Space plants widely for air circulation, which helps minimize powdery mildew; use the plant spacing calculator.
- Place tall types at the back of a border.
Caring for aster
Stake tall types in late summer. Cut dead stems to the ground in late winter. See the garden watering calculator for watering.
Companion plants
| Grow nearby | Goldenrod, coneflowers, ornamental grasses and sedum |
|---|---|
| Keep apart | Crowded, still-air sites |
Named New England aster cultivars include 'Alma Potschke' and 'Purple Dome'; 'Professor Kippenburg' is a New York aster. Check other pairings with the companion plant finder.
Common problems
| Problem | What you see | What to do |
|---|---|---|
| Powdery mildew | White coating on leaves in late summer | The Wisconsin source recommends wide spacing for air circulation. See the pest identifier. |
| Floppy tall plants | Stems flopping in late summer | Stake tall types in late summer. |
Not sure what you are looking at? The plant problem identifier ranks likely causes from the symptoms you see.
When and how to harvest
Asters are grown for fall color. Divide clumps every two or three years to keep them vigorous.
Plan your aster
- Plant spacing calculator: how many plants fit your bed
- Planting calendar: sowing and transplant dates for your frost dates
- Frost dates by ZIP code: your last spring and first fall frost
- Harvest date calculator: when your crop will be ready
Frequently asked questions
How far apart should I plant asters?
Space asters 24 inches apart in rows 24 inches apart. In a square foot garden, plant 1 per square foot.
How deep do I plant aster plants?
Plant asters in spring, spaced widely for air circulation in full sun or part shade.
How long do asters take to grow?
Asters bloom late in the year, into fall.
How much water do asters need?
About 1 inch of water a week, from rain and watering combined. Provide moist, well-drained soil.
When should I divide asters?
Every two or three years, in spring.
How do I reduce powdery mildew on asters?
Space plants widely for good air circulation.
When do I cut asters back?
Cut dead stems to the ground in late winter.