Planting
Where to Plant Asters
Asters prefer areas with cool, moist summers and cool nights in sites with full to partial sun. In warmer climates, asters do not like the hot midday sun. Soil should be moist but well-draining and loamy. Wet clay soil will lead to root rot, and dry sandy soil will lead to plant wilt. Mix 2 to 3 inches of compost into the soil before planting.
When to Plant Asters
- The best time to put young aster plants in the ground is in mid- to late spring after the danger of frost has passed. (See local frost dates.)
- Or you can plant mature, potted asters when available at garden centers (typically in the late summer or early fall).
- Asters can be grown from seed, but germination can be uneven. If desired, plant seeds in the fall or start them indoors in the winter.
How to Plant Asters
- When planting young aster plants outside in the spring, space them 1 to 3 feet apart, depending on the type and how large they’re expected to get.
- Fully grown asters, such as those available in late summer or early fall, should be planted about 3 feet apart.
- If planting seeds, sow 1 inch deep in pots or flats and refrigerate them for 4 to 6 weeks to simulate winter dormancy. This cold period will kick-start germination.
- Water well, and spread mulch around the plants to keep the soil cool and prevent weeds.
Types
Even though there are more than 600 aster species, the most common asters available in North America are the New England aster (Symphyotrichum novae-angliae) and the New York aster (S. novi-belgii). Both of these plants are native to North America and are great flowers for pollinators. We recommend planting a native species of aster over a non-native species when possible, so talk with your local Cooperative Extension or garden center about which species are best suited to your area. Look for varieties with disease resistance.
North American Asters
- Aromatic aster (Symphyotrichum oblongifolium): Multi-branched at the base, stiff upright stems, with lavender or pink flowers.
- Blue wood aster (S. cordifolium): Bushy with small, blue-to-white flowers.
- Heath aster (S. ericoides): A low-growing ground cover (similar to creeping phlox) with small, white flowers.
- New England asters (S. novae-angliae): Varieties have a range of flower colors, from magenta to deep purple. They typically grow larger than New York asters, though some varieties are smaller.
- New York asters (S. novi-belgii): There are many varieties of New York asters available. Their flowers range from bright pink to bluish-purple and can be double, semi-double, or single.
- Smooth aster (S. laeve): A tall, upright aster with small, lavender flowers.
European/Eurasian Asters
- Frikart’s aster (Aster x frikartii) ‘Mönch’: Hailing from Switzerland, this mid-sized aster has large, lilac-blue flowers.
- Rhone aster (A. sedifolius) ‘Nanus’: This aster is known for its small, star-shaped, lilac-blue flowers and compact growth.
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Comments
Hi Donna,
I suspect they died from overwatering. I suggest starting over with new plants. Water them when you plant them, and then wait until they dry out a bit before giving them a good soaking. Plants like less-frequent, deep watering. Also, pay attention to the weather and the moisture level of the soil. Some weeks you will water more, others less. Air temperature and rainfall really determine how much water your plants need from week to week.
Hi Dana,
Do not overwater. Just keep the soil moist. Use a spray bottle so that you don't disturb the seeds too much. We suggest that you cover the pots or trays with plastic. This will keep the soil moist so that you don't need to water. You should see new growth after about 10 days. When the seedlings emerge remove the plastic and mist the soil lightly. Put the plants in your sunniest window. When the seedlings have their first leaves transplant into bigger individual pots.
Yes, you can cut off the dried out dead branches. This is normal for asters. As soon as the weather warms up you should see some new growth from the bottom of the plant.
Asters grow best in full sun and in moist well-draining soil. Make sure the soil is not too wet. Please see our planting and care tips at the top of this page.
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You can either leave them in the pots outside (do not bring them in) and plant them in the early spring or go ahead and plant them now, but do it soon, as night temperatures are dropping fast! Either way, they require a cold dormancy period so they must stay outside.