Introduction
Yes, dahlias can be kept indoors, but they need very bright light or grow lights and they still need a dormant rest period. Whether you want to get a head start on the growing season, keep a favorite variety safe through a cold winter, or try your hand at growing them as houseplants, we have the answers you need. At Longfield Gardens, we want to make it easy for you to enjoy these spectacular flowers, including everything from petite blooms to massive dinnerplate dahlias. This guide will help you understand the specific needs of dahlia plants when they are grown inside the home.
Quick Summary
- Indoor dahlias are achievable but require intense natural or supplemental light.
- Compact or "border" varieties are the best choice for indoor containers.
- Starting tubers indoors can jump-start your season by several weeks.
- Overwintering is a dormancy phase, not an active growing phase.
- Indoor-grown plants must be hardened off before moving to the garden.
Can Dahlias Be Grown as Permanent Houseplants?
The short answer is yes, but it comes with a few specific requirements. Dahlias are naturally sun-loving plants that thrive in the open air. To keep them happy as year-round houseplants, you must act as their personal weather-maker.
The biggest challenge is light. Most indoor spaces do not provide the intensity these plants need to produce blooms. If a dahlia does not get enough light, it will become "leggy", meaning the stems grow thin, weak, and tall as they stretch toward the nearest window. To successfully grow them as houseplants, you will likely need to supplement natural window light with a high-quality grow light.
Another factor is the dahlia’s life cycle. Even indoors, the plant will eventually want to rest. You may notice the foliage beginning to yellow or die back after several months of blooming. This is a normal part of the plant's rhythm and not a sign of failure.
Choosing the Right Varieties for Indoor Pots
If you want to keep a dahlia plant indoors, the variety you choose makes a massive difference. Large dahlias are usually too cumbersome for a windowsill. Instead, look for dwarf or "mignon" varieties, such as border dahlias. These typically reach only 12 to 18 inches in height.
Compact varieties are much easier to manage in a container and are less likely to fall over. They still produce plenty of flowers in bright, cheerful colors. We have found that these smaller types are the most rewarding choice for indoor enthusiasts.
Key Takeaway: While dahlias can be kept as houseplants, they require intense light and will still need a dormant period to stay healthy over the long term.
Starting Dahlias Indoors for an Early Start
One of the most common reasons to keep dahlia plants indoors is to "pre-start" them in late winter or early spring. By starting your tubers in pots indoors about 4–6 weeks before last frost, you can enjoy flowers much earlier in the summer.
When to Begin the Process
Timing is everything. If you start them too early, they may become too large for their pots before the weather is warm enough to move them outside. Look up the average last frost date for your area and count back six weeks. For example, if your last frost is typically in mid-May, you can start potting up your tubers in early April.
Preparing Your Indoor Growing Space
To start tubers successfully, you need a spot that is warm and bright. A south-facing window can work, but grow lights are even better. You can use simple shop lights to provide a full spectrum of light.
Keep the lights about six inches above the tops of the pots, raising them as the plants grow. Using a timer to provide 12–14 hours of light each day mimics the long days of summer and encourages bushy, strong growth.
The Potting Process
Choose a container that fits the size of the tuber clump with an inch or two of space around the sides.
- Use a High-Quality Potting Mix: Choose a loose, well-draining soilless mix.
- Check the Tubers: Look for "eyes"—small bumps near the stem where new growth will emerge.
- Planting Depth: Fill the pot about one-third full with moist soil. Lay the tuber horizontally with the eyes facing up. Cover with another inch or two of soil.
- Water Sparingly: Do not soak the soil at first. A light misting is enough to "wake up" the tuber. Too much water before roots have formed can cause rot.
What to do next:
- Determine your local last frost date.
- Set up a dedicated area with grow lights and a stable surface.
- Purchase a high-quality, well-draining potting mix.
- Inspect your tubers for firm skin and visible eyes before planting.
Overwintering Dahlias Indoors
If you live in Zone 7 or colder, you will need to bring your tubers indoors to keep them alive for next year. This is a form of overwintering them indoors that focuses on preservation rather than active growth.
Digging and Cleaning
Wait until the first frost has turned the foliage black or brown. Cut the stems down to about three or four inches. Carefully dig up the root ball and gently shake off excess soil. If you wash them, ensure they are completely dry before storage.
Storage Conditions
The goal is to keep the tubers in a state of "suspended animation." They need to stay cool enough to remain dormant but warm enough that they don't freeze. The ideal temperature for 40–50°F storage is an unheated basement, crawl space, or cool closet. You can store them in cardboard boxes or paper bags filled with slightly damp peat moss or wood shavings.
Checking Your Tubers
Check on your stored tubers once a month. If they look shriveled, give them a very light misting. If you see any soft or mushy spots, remove those tubers immediately to prevent rot from spreading.
Essential Care for Indoor Dahlia Plants
Indoor dahlia needs differ from those of outdoor plants. Because the environment is controlled, you must be diligent about providing the right balance of resources.
Light: The Most Important Factor
Light is the engine that drives dahlia growth. Indoors, the sun's rays are filtered through glass, which reduces their strength. Aim for at least 6 to 8 hours of direct, intense light. Grow lights should be left on for 12–14 hours of light a day to compensate for the lower intensity of artificial bulbs.
Watering and Humidity
Container-grown dahlias dry out faster than those in the ground. However, they are sensitive to "wet feet." Only water when the top inch of soil feels dry. When you do water, do so thoroughly until water runs out of the drainage holes, then empty the saucer.
While dahlias don't need tropical humidity, they do appreciate some moisture in the air. Grouping plants together or using a small humidifier can keep the foliage from becoming brittle.
Airflow and Pests
Indoors, air can become stagnant. A small fan on a low setting can help prevent powdery mildew. Keep an eye out for common indoor pests like spider mites or aphids. If you see fine webbing or sticky spots, treat the plant with insecticidal soap or neem oil.
Key Takeaway: Successful indoor dahlia care relies on maximizing light, managing moisture levels carefully, and ensuring adequate air circulation to prevent pests and disease.
Transitioning Dahlias from Indoors to Outdoors
If you have kept your dahlia plants indoors to get a head start, you eventually need to move them outside. Plants lived in a pampered environment are not yet tough enough for direct wind and intense sun.
The Hardening Off Process
This process is called hardening off. Start by placing your pots in a sheltered, shady spot outside for just an hour or two. Over the course of 7–10 days for hardening off, gradually increase their time outside and exposure to sunlight.
When to Plant in the Ground
Once your plants are hardened off and the 60°F soil threshold is reached, you can transplant them into the garden. Dahlias love warm soil, so there is no rush. Waiting for the right temperature results in faster, healthier growth.
Key Takeaway: Transition plants to the outdoors over 7–10 days for hardening off, ensuring the danger of frost has passed and the ground has warmed to at least 60°F soil before transplanting.
Common Questions About Indoor Dahlias
Many gardeners wonder if they can keep a dahlia blooming all through the winter. While theoretically possible with professional-grade lighting, dahlias are biologically programmed to rest. Forcing them to bloom year-round can eventually weaken the tuber.
Regarding fertilizer, wait until the plant is actively growing and has several sets of leaves. A balanced, water-soluble fertilizer applied at half-strength every two weeks is usually sufficient for container-grown plants.
Creating a Successful Indoor Environment
Drainage is non-negotiable for indoor containers. If your decorative pot doesn't have holes, keep the dahlia in a plastic "nursery" pot with drainage inside the decorative one. "Azalea pots," which are slightly shorter and wider, provide a stable base for dahlias that can become top-heavy.
Dealing with "Leggy" Growth
If your dahlia has already grown tall and thin, you can fix it by pinching back the central stem. When the plant is 8 to 12 inches tall, use snips to cut off the top few inches of the main stem just above a set of leaves. This encourages the plant to grow "out" rather than "up," which fixes "leggy" growth and results in more bloom sites.
What to do next:
- Check the drainage of your pots.
- Monitor stem thickness to decide if you need to move lights closer.
- Prepare to "pinch" the stems once they reach 8-12 inches.
- Ensure you have a plan for transitioning plants outdoors if that is your ultimate goal.
Conclusion
Keeping dahlia plants indoors is a rewarding way to extend your gardening season. Whether you are starting tubers early, overwintering them, or enjoying a dwarf variety on a windowsill, these plants can adapt with the right care. By focusing on high light levels, careful watering, and a gradual transition, you can enjoy their spectacular beauty year after year.
Our dahlia collections are here to help you succeed.
- Select compact varieties for permanent indoor displays.
- Provide 12–14 hours of light for the best results.
- Monitor soil moisture closely to avoid tuber rot.
- Always follow the 7–10 days for hardening off rule before moving to the garden.
For more inspiration and high-quality tubers, we invite you to explore our selection. Happy growing!
FAQ
Can I keep a dahlia plant as a houseplant all year?
While it is possible to keep a dahlia indoors, it is quite challenging because they require very high light levels and have a natural need for a dormant period. You will need strong grow lights to keep them healthy, and the plant will eventually need to rest for a few months by drying out and losing its foliage.
Why is my indoor dahlia growing tall and skinny?
This is usually a sign that the plant is not getting enough light. When dahlias don't receive 6–8 hours of direct sun or intense grow lights, they stretch out to find a light source, resulting in weak, "leggy" stems. Moving the plant to a brighter spot or adding a grow light will help it grow stronger and bushier.
How often should I water a dahlia tuber planted indoors?
You should water very sparingly at first. Until the tuber has developed roots and sent up green shoots, it cannot process much water, and excess moisture will cause it to rot. Once you see active growth and several inches of leaves, you can begin watering more regularly, whenever the top inch of soil feels dry.
When should I bring my indoor-started dahlias outside?
You should wait until the danger of frost has completely passed and the soil temperatures are consistently warm. Before planting them in the ground, you must "harden them off" by gradually exposing them to outdoor conditions over 7 to 10 days so they can adjust to the wind and sun.
