How to Grow Large vs Small Aster Flowers (Care Tips)

I’ve killed more asters than I care to admit. Honestly, it took me two full seasons to figure out why my small asters looked weak and my large ones refused to bloom. After trial and error, I finally cracked the code. Here’s the straight answer: large asters thrive with consistent deep watering and full sun, while small asters need well-drained soil and partial shade to avoid root rot. I learned this the hard way—by watching my plants turn yellow and collapse. Let me walk you through exactly what I did over two weeks, including the mistakes that nearly killed them.

The Three Deadly Mistakes Newbies Make (I Made All of Them)

Before we get into the nitty-gritty, I have to warn you about three errors that destroy asters. I personally messed up each one, and it cost me plants.

1. Overwatering: The Silent Killer

I once watered my asters every day for a week. I thought I was being helpful. Instead, I drowned them. Within days, leaves turned mushy and stems collapsed. Then I learned the hard truth: 90% of indoor plants die from overwatering. For asters, this is especially true for small varieties with shallow roots. I now stick my finger an inch into the soil. If it’s wet, I wait. Simple as that.

2. Wrong Light Placement

My first batch of large asters went on a shady balcony. They stretched tall, looking leggy and sad. They barely flowered. Then I moved them to full sun—six hours direct light. Within a week, buds formed. Meanwhile, my small asters burned under that same sun. I had to shift them to partial shade. Light isn’t one-size-fits-all for asters.

3. Using the Wrong Pot

I once planted small asters in a huge ceramic pot. The soil stayed wet for days, and roots rotted. Big mistake. Large asters need deep pots for their root systems, but small asters prefer shallow, wide containers with drainage holes. I switched to terracotta for small asters—it dries out faster. Game changer.

My Two-Week Obsession: Growing Large vs Small Asters Step by Step

I decided to run a little experiment. I planted three large aster cuttings and three small aster seedlings. I tracked everything for 14 days. Here’s what happened.

Week 1: Day 1 to Day 7

Day 1: I prepped two separate areas. Large asters got a spot with full sun from 7 AM to 1 PM. Small asters went under a light shade cloth that filtered afternoon heat. Soil mix? I used a gritty, fast-draining blend for small ones—one part potting soil, one part perlite, one part sand. For large asters, I added a bit of compost for nutrients.

Day 3: I watered the large asters deeply—until water ran out the bottom of their 12-inch pots. Small asters got a light sprinkle on day 3, just enough to dampen the top inch. I noticed large aster leaves perked up, while small ones still looked slightly droopy. I panicked and watered more. Bad call. By day 5, the small asters’ lower leaves turned yellow. I had overwatered again. I stopped watering entirely for two days and let the soil dry.

Day 7: Large asters grew about two inches taller. Small asters stayed compact but showed new leaf buds. I trimmed one wilted leaf off a small aster. It recovered fast. Lesson: small asters hate wet feet.

Week 2: Day 8 to Day 14

Day 8: I checked soil moisture. Large aster pots were dry two inches down—time to water again. Small aster pots were still damp at one inch. I skipped their watering. Instead, I misted the leaves lightly in the morning. That seemed to help humidity without drowning roots.

Day 10: I noticed small asters had tiny buds. Large asters were still leafy. I pinched off the top growth of the large asters—a trick I learned from a RHS guide. This encourages bushier growth and more flowers later. For small asters, I didn’t pinch. They naturally stay compact.

Day 12: Large asters looked robust with thick stems. Small asters had three open blooms each—tiny, delicate purple petals. I confess, I got excited. But then I saw a few aphids on the large asters. I sprayed them with a mix of water and a drop of dish soap. It worked within 24 hours. Aphids hate soap.

Day 14: Final results. Large asters stood 18 inches tall with dark green leaves. No flowers yet—they’re late bloomers. Small asters reached 8 inches, covered in flowers. Both looked healthy. But here’s the kicker: the large asters needed watering every 4 days, while small asters only needed it every 7 days. Overwatering would have killed them again.

Why You Need to Choose Your Aster Variety Carefully

I’ve learned that not all asters behave the same. The key difference comes down to root structure and growth habit.

Large asters (like Aster novae-angliae) have deep, aggressive roots. They need space to spread. I’ve seen them double in size within a month if given enough room. They also require more nutrients—I add a slow-release fertilizer every spring. Many experts from the AHS recommend this for robust blooms.

Small asters (like Aster alpinus) are alpine plants. They evolved in rocky, dry soil. Their roots stay shallow. If you put them in a deep pot with rich soil, they rot. I lost two pots before I understood this. Now I use shallow containers and water sparingly.

The Soil Equation: It’s Not Complicated

I used to think “well-drained soil” was just a fancy term. Then I watched my small asters suffocate in heavy garden soil. Here’s what I do now:

• For large asters: Mix 2 parts garden soil, 1 part compost, 1 part coarse sand. This holds moisture but drains fast.
• For small asters: Mix 1 part potting soil, 1 part perlite, 2 parts sand. This dries out within 24 hours after watering.

I tested this by watering both pots and checking moisture after two days. Large pot stayed damp. Small pot was dry. Perfect.

My Personal Struggles: I Killed 3 Plants Before I Got It Right

I want to be real with you. I’m not a pro. I’m just someone who kept making mistakes.

My first year, I planted a mix of large and small asters in the same bed. The large ones overshadowed the small ones, blocking light. Within weeks, the small ones got leggy and died. I felt awful.

Then I tried growing small asters indoors near a south-facing window. The glass magnified heat, and leaves burned crispy. I moved them to an east window—gentler morning sun. That worked.

The worst mistake? I once repotted a large aster into a pot that was too small. Roots circled inside, and the plant stunted. I had to cut the pot off and divide the root ball. Messy and stressful. Now I always choose a pot that’s at least 2 inches wider than the root ball for large asters. For small, 1 inch wider is plenty.

Watering Schedule: What I Actually Do

I keep a simple journal on my phone. Here’s my exact schedule after 2 weeks of observation:

Large asters:

• Water deeply every 4-5 days during growing season.
• Check soil at 2 inches deep. If dry, water until it drains.
• Reduce to every 7-10 days in fall.

Small asters:

• Water lightly every 7 days.
• Never let water sit in the saucer.
• If leaves droop slightly, I wait one more day before watering—they bounce back fast.

I tested this with a moisture meter. Large asters liked readings around 4-5 (moist). Small asters preferred 2-3 (drier). Simple numbers saved my plants.

Light Requirements: A True Story

I initially thought all asters needed full sun. I put my small alpine asters on a south-facing balcony. They got eight hours of direct light. By day 5, leaves curled and turned white at the edges—sunscald.

I moved them to a spot with morning sun and afternoon shade. Recovery took about a week. Now they bloom happily with 4 hours of direct light.

Meanwhile, my large asters on that same south balcony thrived. They soaked up all that sun and grew like weeds. So remember: large asters are sun lovers. Small asters are sun wimps.

Fertilizer Lessons: Less Is More

I once dumped fertilizer on my small asters thinking they’d bloom bigger. Nope. They grew lots of leaves but no flowers. Too much nitrogen. I stopped fertilizing completely for two weeks. Then I used a low-nitrogen, high-phosphorus blend (like 5-10-10). That pushed buds.

For large asters, I use a balanced 10-10-10 fertilizer once a month during active growth. Stop in late summer to let them harden off for winter.

Common Pests and How I Handled Them

Asters attract aphids and spider mites. I saw both on my plants.

Aphids: I spotted them on large aster stems. A strong spray of water knocked them off. Then I used neem oil once a week for two weeks. All gone.

Spider mites: These hit my small asters when the air was dry. I increased humidity by placing a tray of pebbles with water under the pot. Also, I misted leaves daily. Mites hate humidity.

FAQ: Questions I Asked Myself (And You Probably Have Too)

1. Can I grow large and small asters together? Technically yes, but I don’t recommend it. Large ones outcompete small ones for light and water. I tried it, and the small ones suffered. Keep them in separate pots or beds.

2. How do I know when to repot asters? Look for roots coming out of drainage holes. For large asters, repot yearly in spring. For small asters, repot every 2 years—they like being root-bound. I learned this after a small aster barely grew in an oversized pot.

3. Why are my aster leaves turning yellow? Overwatering is the top reason—90% of indoor plants die from overwatering, remember? But also check for poor drainage. I had yellow leaves on my small asters when the soil stayed wet for a week. I simply stopped watering and added more perlite. Fixed within 10 days.

Final Thoughts from My Garden

I no longer guess with my asters. Large ones get deep pots, full sun, and consistent watering every 4 days. Small ones get shallow containers, partial shade, and barely any water. It took me a full year and three dead plants to figure this out, but now I can grow both without panic.

Start small. Watch your soil. Trust your finger test. And please, don’t water every day—your asters will thank you.