Is there anything as glorious as a dahlia in full bloom? Lush, vibrant and colorful, this exceptional plant is surprisingly easy to grow – you don’t need to be an expert. Here are some tips on how to plant, grow and care for dahlias.
Planting Dazzling Dahlias
When should I plant my dahlias?
Soil—not air—temperature is the key to healthy, beautiful dahlias. You’ll want the soil temperature to be 60 degrees or warmer. For the coldest Northern states, your soil won’t be ready until May, while those enjoying warmer climates might be good to go as early as March. Resist the temptation to plant them earlier than advised: your tubers may just rot. To determine whether your soil is ready, buy an inexpensive soil thermometer, and test the soil mid-morning. Basically, if you can garden in a t-shirt, you’re probably ready to start growing!
Where should I plant them?
Like petunias, sunflowers, and lavender, your dahlias will thrive on generous sun exposure. Choose a place in your garden that receives 6 to 8 hours of sun a day. If you live in a very hot climate, a little afternoon shade can’t hurt. If you’re struggling to find a patch of land that gets full sun, try the lower growing or dwarf dahlias. The more sun, the more flowers you’ll get.
Healthy Soil, Healthy Plants
What sort of soil should I have?
Whether you’re planting in the ground or in a pot, you’re ready to plant your dahlias if your soil is:
- Slightly acidic. Aim for a PH level of 6.5 – 7. Add lime to increase the level, or sulfur to decrease it.
- Well-drained. Avoid planting dahlias in soil that pools after it rains. Too much water will cut off the oxygen your tubers need.
- Healthy. Give it a boost of nutrients with cow manure.
- Free of herbicides. Make sure your potting soil hasn’t been sterilized. Even if a herbicide claims to be safe for flowers: don’t use it. Always hand weed. Also, add compost sparingly. Compost tends to be high in nitrogen, which produces less robust, full plants.
- (If you live in a hot climate) Slightly damp. Just a little moisture is enough.
Planting your Dahlias
How do I plant my dahlias?
If your tubers have any sprouts attached to them that are longer than 1”, carefully trim them back to just 1”. Plant your tubers in holes that are 6 inches deep, and 18-24 inches apart, depending on how big the varietal you’re planting. Insert your garden stakes right next to each tuber. Any kind of stake is fine (metal, wood, plastic etc.), and it is best to stake now before they sprout. Throw in a handful of bone meal—it’s a great fertilizer and source of phosphorus and protein—but only if you don’t have pets. (Rover and Fluffy might dig it up.)
Don’t cover your garden bed with mulch or bark dust, because you need the sun to keep the soil nice and warm. Add snail and slug bait — dahlias do tend to attract slugs. Unless you live in a hot climate, you don’t need to start watering until after your tubers have sprouted, which will be in 3 to 5 weeks. Seriously! Over-watering is one of the main reasons dahlias fail to bloom.
Containers and Pots
Can I grow dahlias in a container?
Even though dahlias do grow best in the earth, rest assured, you can grow them in a pot. Try the low growing and dwarf varietals: they don’t need as much space and soil. A 12 x 12-inch pot is fine for these types. Aim for two parts garden or topsoil, and one part potting soil.
Watering Your Plants
How often should I water them?
After your dahlias are above the ground, they’ll need a deep watering 2 to 3 times a week: enough moisture to reach your planted tuber. A hose is best. Remember, you only need to water unsprouted tubers if you live in hot, dry climates like Texas or Southern California: in this case, water lightly once or twice a week.
Fancy some Fertilizer?
Should I fertilize my dahlias?
If you choose to use a fertilizer, go for a low nitrogen or slow release type. Use cow or steer manure at any point in the planting/growing process. Get the processed/bagged kind. Only add fresh manure in the fall, so it has time to break down before spring. For commercial fertilizers, again, go for low nitrogen and high in potassium and phosphorous, something like a 5-10-15 or 5-10-10. Fertilize within the first month of planting, then repeat again 3 to 4 weeks later: don’t overdo it.
The Need to Weed
How should I weed my dahlias?
The thing about weed killers is, if they kill the weeds, they also kill your dahlias. Hand weeding is the best, low-impact way to keep weeds out of your garden beds. If you absolutely must use a commercial weed-killer, try something like Round-Up but only after your tubers have sprouted, and be careful not to spray the plant itself.
How should I top my plants?
If you want to display your dahlia flowers indoors, then you’ll want the best possible stem length. Simply cut the center shoot just above the third set of leaves, when your plant is about twenty inches tall. This will help bloom a shorter, bushier plant.
Digging & Storage
How should I dig and store my dahlias?
After your dahlias have turned black from frost, snip the stems at about 6 inches, and carefully dig out your now sizable tubers. Wash off the dirt and leave them in the sun to dry. Then pack them in some peat moss, sand or sawdust in a paper bag or box: never plastic and never fully sealed. Store them in a cool, dry area (not a freezer) until you’re ready to plant next spring. If you live in a mild climate, you can try leaving them in the ground: just cover the surface with mulch or similar, to protect the soil from rain and freeze.
Divide (and Conquer)
How do I divide my dahlias?
Cut your tuber clump with a sharp knife to separate out the roots: each root must have an “eye” located in the center stalk in order to grow. You can do this in the spring or the fall. If you can’t see the eye (and not all tubers have one), try dividing your clump into halves or quarters.