Our Guide to Growing Dahlias
what to do when your tubers arrive
Open your box immediately to check your tubers. Our tubers are packed by variety in pine shavings with a plant label. Condensation may form in the box/bag during transit. If you see this, you can open the bags slightly to let the trapped moisture out so that your tubers stay in good condition. If your climate allows (read section “Timing”) you can plant the tubers as is. If you still have time before it is safe to plant outside you will need to store your tubers or pot them up in containers for a head start. If starting in pots indoors, we recommend starting about a month before you plan on planting outside.
To store: keep your tubers in their bags and in a frost-free area (40-45 degrees). The warmer your storage area, the faster your tubers will develop sprouts called eyes. Check on your tubers periodically to make sure condensation isn’t forming in the bags and that they aren’t drying out. If condensation is forming, you can poke a hole in the bag or open it slightly to let the moisture out. If your tubers are drying too much, you can add a light spritz of water in the bags so the shavings are barely moist.
Timing
Choosing the right time to plant is the key to a successful dahlia crop. Dahlias prefer warm soil. Plant after all danger of frost (enter your zip code here to find your last frost date) has past and when soils have warmed to at least 55-60 degrees. If the forecast is predicting a prolonged stretch of wet weather, it is best to hold off on planting as tubers are prone to rot in cold/wet soils. In the Northeast, mid-May is typically the earliest we can plant outside. Plant dahlias around the same time you would plant tomatoes in your vegetable garden. If you want earlier flowers, you can start your tubers indoors in pots about a month before planting outdoors.
If starting tubers in containers indoors, water your tuber once after planting and leave in a warm, sunny location. Your soil should be moist, not wet (refer to section “Watering Dahlias”).
Site preparation
Dahlias thrive in full sun and should be planted in a location that receives a minimum of 8 hours of sunlight a day. Dahlias planted in an area with less sunlight will grow taller and won’t yield as many blooms. If you live in an area with hot summers, dahlias will appreciate a partly-sunny spot to shield them from the sun during the hottest parts of the day.
Dahlias are heavy feeders and like soil with lots of organic matter. Because tubers are prone to rot, it’s important to make sure that your soil isn’t too heavy and drains freely and easily; if not, amend it with peat moss or sand.
Planting Tubers
Single dahlia tubers will grow into a clump and multiply quite substantially over the course of the season, so it is important that you prepare your soil well to accommodate such growth. Start by digging a hole at least 8” wide and 12” deep. We choose to incorporate an organic balanced fertilizer (find our proprietary mix here) at planting time, but depending on the results of your soil test, you may need to amend your soil with more/less nutrients (nitrogen, phosphorous, potassium, etc). Mix approximately 1/4 cup of the fertilizer in with some of the soil you removed before planting tubers horizontally, with the eye(s) facing up, about 4 to 6 inches deep. We space dahlias at 12" apart, with dinnerplate and larger-headed dahlias spaced at least 18-24” apart. All dahlias that we sell will require additional support (tomato cages or bamboo stakes work well).
Watering Dahlias
Once you plant your tubers, wait to water until you see the first shoots emerge. If you are planting outside there usually is enough residual moisture in the soil to get your tubers to start growing. If you are planting in a container or your soil is dry, water well once at planting, then hold off on watering again until shoots emerge. Tubers need a little moisture to being sprouting but too much moisture will make the tuber rot. It is a delicate balance. Remember that different dahlia varieties take different times to sprout. Early-blooming varieties can take as little as 2 weeks to sprout while other varieties (especially dinnerplates) can take as long as 2 months!
Young dahlia plants do not require much water. Once your dahlia plants are established (8-12” tall), water regularly and deeply. A good rule of thumb is that your dahlias should receive 1” of water every week. In the heat of summer, dahlias will require more water especially if it is warm and dry. When they are actively growing and blooming, dahlias will need more water. Dahlias grown in pots will require more frequent, daily watering.
Fertilizing dahlias
We amend our soil with an organic fertilizer mix at planting time. Once dahlias begin to bloom, we foliar feed every other week with a fish and seaweed formula (low nitrogen). Because our fertilizer blend includes slow-release nitrogen, we avoid giving our plants more food high in nitrogen once they begin to bloom.
Topping (Pinching Dahlias)
A regular practice for dahlia growers is to pinch or “top” your dahlia plants to promote lateral growth and a more balanced plant (one that isn’t too top heavy). When your plant is about 12” tall, snip out the growing tip, leaving 3-4 pairs of leaves (counting from the bottom). This will encourage the plant to send up low basal growth that will not only give you more flowers to cut, but also distribute the weight of your plant better so they are less likely to topple in strong winds and rains. Note: supporting your dahlia is paramount. If you are a home gardener, tomato cages or bamboo stakes work well. If you are growing in large amounts, corralling your plants with tomato twine and T-posts spaced every 6-8 feet or using "‘Hortonova’ netting is recommended.
Harvesting Dahlias
The best time to cut dahlias is in the cool of the morning or evening. Using sharp pruners, cut the stem at a 45 degree angle just above a leaf node. (A good stem length is from the tip of your finger to the crook of your elbow). The plant will branch just below the cut and produce additional stems. Harvest dahlias when the flower is nearly or fully open. Closed buds won't open after the stem is cut. Strip any foliage that will be below the waterline in a vase. Place the stems in fresh water and add flower food as desired. Replace the water and recut stems daily for a vase life of 3-5 days (vase life of dahlias varies depending on variety and size).
Harvest or deadhead dahlia plants regularly to promote additional flowering. Once flowers go to seed, the plants will slow down flower production.
Digging dahlias
In the Northeast, our winter temperatures are just too cold, and dahlias’ thin-skinned tubers will freeze if left in the ground over winter. Tubers can be pulled each fall, cleaned, and stored in a cool, dark room until next spring (see “Storing Dahlias” below). After a hard frost has killed the plant, cut the dahlias down close to the base, leaving about 6” of stem as a handle to help you pull the tuber clump up. We have better success storing our tubers over winter when we let our tubers “cure” in the soil for at least 10-14 days after a hard frost before digging. Waiting is not necessary, however, and tubers can be lifted the same day they are cut down. You should do what works for you and your schedule!
Starting at least 6” away from the heart of the plant, use a digging fork to gently lift your tuber clump out of the ground being careful not to break the tuber’s necks. We find that you will need to “dig” 2-3 times around the plant to get the whole clump out intact.
Storing dahlias
It's important to keep tubers clean and maintain a balanced level of humidity in storage over the winter. Tubers should be kept in a cool (40-45 degree), dark place with 85-90% humidity. They are fleshy and water-filled and cannot freeze. How you store your dahlias will depend on your storage location and winter weather conditions. If you’re planning on storing your tubers in a place that is dry you may need to store tubers in airtight containers with a packing medium (pet shavings, vermiculite, etc). If your storage space is wetter (i.e. in an unfinished basement) or you live in a rainy climate, you may find more success leaving your tubers in an open box with no packing medium. There is no single way for storage success. You will have to check on your tubers frequently/weekly to check for rot or shrivel. Tubers that have properly hardened off will maintain their firmness in storage and are neither shriveled (storage location too dry) or moldy (storage location too wet). Know that there is no “right” way to store tubers. The key is to maintain temperature and humidity.
Sourcing Dahlias
Dahlia tubers are readily available from many growers online. Tubers are essentially the root stock of the dahlia plant and, once planted, will multiply in the ground every season. A dahlia plant grown from one tuber will yield multiple tubers once dug up in the fall. We sell our excess tuber stock in late winter/early spring. Join our mailing list to be notified when our dahlias will go on sale!