How to Grow and Care for Dahlias
Digging Up and Storing Tubers
What to do for your dahlias at the end of the season
After the first hard frost and the dahlia foliage has blackened, cut the plants to 4”-6” (later you’ll use the stalk as a handle for the clumps). Leave the tubers in the ground for a week for the sprouts/eyes to develop on the tubers. Tubers dug too early are still “green” and will not store, while leaving them in the ground will allow for their skin to harden as it cures, like a potato. If you haven’t experienced a frost by mid-November it’s safe to dig the tubers at that time. Gently dig the tubers about 8” to 10” from the stem, shake off the excess soil carefully and wash off any soil. Allow them to air dry in an area protected from rain and frost for a few days. This air drying toughens the skin of the tuber for winter storage. Be sure to clean up the old foliage from the garden.
Storing your dahlia tubers
Pack the tubers in a loose, fluffy material like slightly dampened peat moss or vermiculite in a paper bag in the basement. Use enough peat moss or vermiculite so the tubers aren’t touching each other. Store in a cool, dry, dark area (temperatures 40-50°F). If you have a lot of tubers to store, we like to use the lawn bags you can buy at the hardware store. Never store the tubers in plastic bags or plastic containers as they require some air flow to avoid rot. Please check your tubers once a month throughout the winter months. If your tubers are rotting they are too wet, if too dry they will be shriveled. If you find a rotten tuber remove it immediately so it doesn’t contaminate other tubers. If the tubers are shriveled, mist the peat moss or vermiculite lightly with water. If you have more than one variety, we suggest labeling each tuber. You can write directly on the tuber with permanent marker or use flagging tape if you have a whole bag of one variety.
Dividing your dahlia tubers
Dividing your dahlia tubers can be done in the fall or spring. If you divide the dahlias in the fall you will have to store them for the winter; you can’t re-plant until the spring. Using a sharp knife, separate healthy tubers from the parent clump. Each tuber must have at least one “eye” or a piece of the crown attached or it will not develop into a blooming plant. You’ll find the eyes at the base of the stem and look like little pink bumps, note that not all individual tubers will have an eye. As long as you have a piece of the stem you’ll most likely have an eye that develops. If the neck of the tuber is broken, you will not have a viable tuber. Think about it like the body of the tuber isn’t connected to the head if the neck is broken, so will not have the brain to tell it to grow. Allow any cut tubers to dry for 24 hours before storing or planting. If you divide in the spring, move the tubers to a warm area for a week to allow the eyes to sprout so they’ll be easier to see.
When should you plant your dahlias?
The most important factor in planting your dahlias is soil temperature. Dahlias struggle in cool soil. After the last frost and your soil temperature is at least 60° go ahead and plant your dahlias. A good time to plant your dahlias is after you would normally plant your tomatoes. Some gardeners start their dahlia tubers in containers inside and plant when the soil warms up.
Where should you plant your dahlias?
Dahlias prefer at least 8 hours of direct sunlight a day, less sun produces taller plants but less blooms. In hot climates, dahlias like morning sun and afternoon shade.
What kind of soil do dahlias like?
Before planting your dahlias have your soil tested for any deficiencies and correct those deficiencies. Dahlias like warm, well-drained soil. If your soil seems heavy and compacted, your dahlias will be very happy if you till the area and add some compost. If you can’t till the area, loosen the soil as well as you can. Dig a hole about 4”-6” deep and lay the tuber horizontally with eyes facing up, spacing the tubers about 18-24” apart and then cover with loose soil. Or for mass production on our scale, we make two trenches 20” apart, and plant the dahlias in the trench every 12”. It sounds close, but if you are cutting off of them hard though the season, it’s enough space for what they need.
After the sprouts appear above the ground you can start watering. Don’t cover the tubers with mulch until after the soil has warmed up and don’t fertilize when planting.
When and how to water your dahlias?
Once your dahlias have started to sprout is when you need to start watering your dahlias. Depending on where you live, how fast your soil drains, and the temperatures should all be factored into how much you water your dahlias. Set up a sprinkler to water because hand watering won’t be enough. Sticking your finger in the ground near the plant is the best way to tell if you need to water. Watering early in the morning is best so the foliage has time to dry off during the day. During the hot summer months you may water 2-3 times per week and 30-60 minutes per day. We typically use drip tape with our dahlias, but watering with a sprinkler is doable as well, just make sure if you do, it is early in the morning so the foliage has time to dry off during the day.
How often should dahlias be fertilized?
Fertilize your dahlias with a low nitrogen fertilizer when the plants are around 6” tall, then again every month until frost. Do not overfeed your dahlias. High nitrogen fertilizers result in a lot of foliage and not a lot of blooms. The blooms are what we are after so make sure your fertilizer is low nitrogen.
What about weeds?
Don’t use any herbicide anywhere near your dahlias – it will kill them. And depending on scale, it may be just hand weeding, hoeing, or mechanically cultivating. We use a combination of tine weeders and belly-mounted baskets on our Farmall (email us if you’re a grower on that scale and want more info). But we also do usually have to hoe and hand weed as well. Since dahlias are in the ground all season, they take a lot of care, but they are worth it! They can be mulched with straw or wood chips to help suppress weeds.
What about pinching or topping your dahlias?
You can pinch or top your dahlias to have bushier plants with strong stems. To do that, cut off the center shoot just above the third set of leaves when the plants are 8”-12”.
When is the best time to cut dahlia flowers?
The best time to cut flowers is in the morning, but you can cut them at any time of the day. Cut the flowers when the buds aren’t too tight. Cut the flowers with clean, sharp pruners and place in water right away. The flowers will stay fresher if you change the water everyday. Don’t forget to remove the old blooms so the plant will produce more blooms until frost. The more you cut dahlia flowers, the more they will bloom.
Do dahlias need staking?
Staking your dahlias will keep your flowers clean and off of the ground and you will have more flowers. You can use any type of sturdy stake you have on hand. It’s best to insert the stake when planting so you don’t have to worry about damaging the roots. We use Hortonova netting on our dahlias to keep the whole row upright. Putting the net on means hand weeding after that, so we typically wait until the plants are about waist high before staking so we can still get hoes in there.