Are dahlias annuals or perennials? It depends on where you live
It’s no wonder that many dahlia growers find themselves wondering, “Are dahlias perennials or annuals?” Dahlias often bloom abundantly with annual favorites such as zinnias and marigolds. From midsummer until frost, flowers will bloom that range from small, petal-filled, button-like blossoms to blooms larger than a dinner plate. However, these plants grow from bulb-like tubers that can survive the winter like perennials. To ensure your dahlias come back next year, you may have to help them, depending on your growing zone. Here’s what you need to know to successfully overwinter dahlia tubers to enjoy year after year.
Are dahlias perennial in your area?
Dahlias are native to the mountains of northern Mexico. It is hardy, or perennial, in tropical and warm climates, and emerges from the ground every spring. In general, dahlias are perennial in zones 8 and above. In zones 7 and below, dahlia’s fleshy roots — called tubers — die because of cold temperatures.
If you garden in zone 7 and below, you don’t have to say goodbye to your dahlias and start with fresh tubers next year. Winterize dahlias by digging them up in late fall and keeping them in a frost-free location until it is time to replant them in the spring.
How to overwinter dahlias
It can be a bit difficult to dig up dahlias and keep them over the winter. In fact, many cold zone gardeners choose to grow dahlias as annuals, purchasing new plants each year. Overwintering dahlias requires patience, persistence, and a little trial and error.
Moisture is a common cause of winter problems. Too much moisture or too little spells doom for dahlia tubers. Poll some dahlia experts, and you’ll get a bunch of tips and tricks for getting the moisture balance right. But at its core, it all boils down to five essential steps for winter success.
Allow the dahlia leaves to die completely to the ground in the fall before digging up the tubers. While a light frost may damage the flowers and some foliage, the plant will continue to grow actively. Wait to dig tubers until the freeze that kills all the foliage has cleared. For best results, keep an eye on the forecast and leave the tubers in the ground for a week or more after freezing the kill to allow them to continue maturing. Dig the tubers once low temperatures regularly drop to freezing.
2. Dig carefully
Dahlia tubers are tender and fleshy, loosely held together by a network of underground stems. Lifting it off the ground requires some gentleness to avoid damaging it. Use a fork or potato shovel to loosen the soil around the entire clump, working at least one foot away from the main trunk. Carefully lift the clump of tubers from the ground and clean off the soil clinging to the individual tubers.
3. Treatment of dahlia tubers
The tubers are very soft when they come out of the ground in the fall. Encourage them to harden off or cure by spreading them out in a shaded, well-ventilated area for a few days. A covered porch or garage can be a great place to treat dahlias. Make sure to protect them from freezing temperatures.
4. Store it well
Moist, well-ventilated storage is essential for dahlia tubers in the winter. A damp but poorly ventilated storage place will cause the tubers to rot. A well-ventilated site without adequate moisture will cause the tubers to dry out and wilt. Experts recommend balancing humidity and ventilation by packing the tubers in a well-ventilated box or basket. Place the tubers upside down, allowing plenty of space between the clumps.
Garden Test Tip: Use a permanent marker to label the tubers with variety names so you don’t have to keep track of labels.
Cover the blocks with a 4- to 6-inch layer of moist vermiculite or fine wood chips, such as commercially sold pet bedding. How moist vermiculite or wood chips are depends on the humidity in your storage area. Start by creating a less wet packing material. Then you can easily add water if the tubers seem to be drying out. Store the ventilated box or basket in the garage, basement, or in a low-temperature area between 35 and 50 degrees Fahrenheit. Avoid places that are hot or cold, very humid or very dry.
5. Check in
Remove the packing material and check the tubers every two weeks. If the tubers appear dry or wilted, mist the media lightly with water. Get a jump start on the growing season by planting tubers in pots about 4 weeks before the last frost date in the spring. Plant them in a bright, sunny window or under grow lights and transplant them into the garden after all danger of frost has passed.