What’s more captivating than a garden full of poofy dahlias!? These gorgeous flowers look beautiful on the plant or in cut floral arrangements. Adding them to your garden is quite easy as long as you know when to plant dahlias since timing is important.
Dahlia plants are members of the Asteraceae family and love sunshine and warm weather. If you live in USDA zones 7-10, these should be pretty easy to grow. You can also grow dahlia flowers inside if you live outside of this range, but it may take some extra work.
You might be a dahlia expert or a member of the American Dahlia Society who grows these beautiful flowers in your cut flower garden. Regardless, cactus dahlias, dinnerplate dahlias, and healthy dahlias in general make lovely cut flowers – large flowers perfect for vase life. Maybe you haven’t grown them, but you love dahlias all the same.
Wherever you decide to plant and grow dahlias, the time and effort put into them will be worth it! Let’s get into when and where you should grow dahlias.
The Quick Answer
Dahlias should be planted when you know you are no longer at risk of frost. These popular flowers originate in Mexico and Central America, so they prefer warmer conditions. Wait about a week after your last frost date, or the date you feel comfortable planting if you know there isn’t a risk of a snapback frost anytime soon.
The Detailed Answer
Plant in the spring, after any danger of frost has passed.
Plant dahlia tubers outdoors in the spring after all danger of frost has passed. Dahlias don’t have much tolerance for cold temperatures, so the weather and the soil should be warm by the time you plant them.
The soil should consistently be 60°F (16°C) or higher so they won’t suffer any frost damage. Cold soil in early spring will prevent them from germinating.
Growing dahlias is ideal in zones 7-10. In these zones, you’ll likely start planting dahlia tubers from April to June. For most areas, it’s best not to plant past June so the weather doesn’t get too hot for the plants to sprout.
This also gives the plants enough time to bloom after the first frost has passed and before the first frost kills them in the spring.
Growing dahlias in containers or in a greenhouse will allow you some flexibility in your planting schedule if needed. Containers will give you the freedom to move them to the light, keep the soil warmer, or bring them indoors if you have an unexpected cold snap.
Greenhouses will allow you to start your dahlias much earlier, especially if you have a climate-controlled setup. Consider using a greenhouse if you live in zones colder than 7.
How to Plant Dahlias
Tubers are planted in the spring in a full-sun location.
Now you know when to plant dahlia tubers, so let’s cover the basics of how to grow them!
If you don’t already know, dahlias produce tuberous roots that can be harvested and divided to propagate them easily. Rather than plant by seed, you can buy dahlia tubers from a store or “borrow” them from a gardener!
Dahlia flowers want lots of sun, so choose a spot that will receive 6-8 hours of direct sunlight. If you don’t have an area that gets this much light, you may want to consider growing dahlias in a container so you can move them around. They can tolerate partial shade, but the results may not be as stunning as you’d hoped for.
The soil should be aerated, well-draining, and fertile. Organic matter like compost or leaf mold will do wonders for the soil and your flowers. Most dahlias prefer rich soil in the garden that can retain moisture and support green growth. Make sure water won’t puddle around the plants, or you’ll risk rotting out the tubers.
It’s important to make sure that the stem around which the tubers are collected is pointed upward. If it’s a single dahlia tuber that you’re planting, it should also have a bit of stem, possibly with some buds or nodules forming on it; that should also be pointed upward. This is where your plant’s greenery will develop, and it’ll push its way through the ground to find sunlight.
Dahlias prefer deep watering after their foliage has started to sprout above ground.
Water dahlias at the soil surface. Deep watering is best, and remember that well-drained soil is also important for growing large dahlias in your garden.
To plant dahlia tubers in your garden, dig holes that are 6-8 inches wide and about as deep to allow the plants to easily spread and grow roots. Space these holes 1-2 feet apart.
In each hole, place one tuber with sprouts pointing up, 3 inches of soil below the surface. Don’t plant the tubers too deep, or they’ll struggle to grow; the depth of the hole is only to make it easier for the plant.
Staking is appropriate for most taller varieties.
It’s a common practice to stake dahlias since many varieties grow rather tall and need some support. You can place a stake in the ground at the time of planting tubers so they can have support from the very beginning.
This will also help you avoid puncturing the tubers since you’ll be able to see what you’re doing. All you need to do is put the stake in the ground beside the tuber and cover the hole with dirt.
Don’t water your dahlia plant too much until dahlias start to emerge from the soil so you don’t rot the tubers. You can fertilize your plants 3-4 weeks after planting them. Don’t give them too much nitrogen, or you’ll risk growing more dahlia foliage than flowers.
Pinching & Deadheading
Pinching & deadheading will help promote healthy plants and flowering.
When the plants are about 15 inches tall, you can try pinching dahlias to remove any terminal buds that appear to promote bushier plants. Terminal buds are at the end of stems, and lateral ones are on the sides. Deadhead dahlias after they bloom, and treat dahlias like you would other flowers in your garden.
You can also make cuttings of your favorite dahlia plant. Rooted cuttings can be planted after the last frost date. When you deadhead, you’ll get more blooms for cut flowers and a bushier plant overall. If you choose not to deadhead, you can gather dahlia seeds from spent blooms.
You may have to contend with powdery mildew if you water from above rather than at the base of the plant. Pests that like to eat dahlia plant matter include spider mites and slugs. You can blast the plant with water to knock off mites, and use organic slug pellets to keep slugs and snails away.
Overwintering and Storing
When you grow dahlias, you don’t have to buy new tubers each year. You can keep your current plants in the ground through the winter or store the tubers and plant them next year!
Overwintering Dahlias Outside
Dahlias can be overwintered outdoors in climates that suit their growth needs.
Dahlia plants are considered tender perennials and can survive the winter in warm locations where it doesn’t freeze too often. Cut the stems back to 6 inches tall about two weeks after they go dormant from the first fall frost.
Once you cut them, you can cover the plants with a few inches of soil or mulch to insulate the ground and keep it warm. Before you cover it, consider removing the mother tuber you planted in the spring. It won’t survive the winter and could end up rotting and causing problems.
If you planted your dahlias in a container, you don’t have much to worry about—just bring them inside! Be sure you have grow lights or a sunny window (or both) to give the plants as much light as possible throughout the winter. You can also bring containers into a greenhouse.
After being pulled from the ground, tubers should be stored in the basement or garage in colder climates.
If you get cold winters in your area, you’ll need to dig up and store dahlia tubers indoors. It’s super simple and won’t require too much extra work!
Just like you would for overwintering, allow the plants to go dormant after the first fall frost. After two weeks or so, dig up all the tubers. Wash the tubers with water to remove dirt and pests and dry off excess water.
Now, allow the tubers to dry out. You can hang them upside down to allow all the moisture to seep out. Be sure to dry them in an area that isn’t too humid and will stay dry.
Once the tubers are wrinkly, they should be good to store. You don’t want to dry them out completely because they need some moisture to stay viable. Keep in mind that wrinkly is good, but crunchy isn’t!
Once the tubers are ready to store, you can decide to divide them now or wait until the spring at planting time. Either way will work! When you divide tubers, make sure each one has an eye so it can develop a sprout. If you have to cut tubers, allow them to dry out so the exposed moisture won’t rot.
Storing dahlia tubers can be done in several different ways, so you can play around with different methods to see what suits your needs the best.
If your winters don’t have long periods of freezing temperatures, you can store the tubers in paper bags in a cool basement or garage as long as there isn’t too much moisture.
For longer storage in cold climates, you can keep them on trays full of sand or peat moss and store them at 40-45°F (4° to 7°C), keep them in a Styrofoam ice chest, or in a heavy plastic bag with packing material.
Whichever method you choose, keep the tubers from touching by storing them with peat moss, sand, cedar chips, or perlite. This will help contain moisture and prevent diseases from spreading. Some gardeners dust their tubers with fungicide before storing them as a preventative measure.
Frequently Asked Questions
Q: Can you plant dahlias in the fall?
A: Planting dahlias begins in the fall in warm areas. Spring is usually the best option since they don’t like soil temperatures below 60°F.
Q: Can I leave dahlias in the ground over winter?
A: You can leave dahlias in the ground in warm climates. However, you will need to mulch them to make sure the ground doesn’t get too cold.
Q: How late is too late to plant dahlias?
A: You shouldn’t plant past June in most hardiness zones. This is because the weather will be too hot, and the plants won’t have a long enough growing season.
Q: Do dahlias grow better in pots or the ground?
A: Dahlias grow well in both pots and in the ground. However, pots will allow you some flexibility you can’t get when you plant in the ground.
Q: Do you have to dig up dahlia bulbs every fall?
A: You’ll need to dig them up if you live in an area that has cold winters with long freezes. You can overwinter them in warmer climates.
Q: Can I plant dahlias straight into the ground?
A: You put a dahlia tuber straight in the ground; there isn’t any need for starting dahlias in containers before placing them in the planting hole in your garden.
Q: Should you soak dahlia bulbs before planting?
A: Dahlia tubers don’t need to be soaked before planting unless they look dried out.