How Often Should You Water Dahlias for Optimal Growth and Blooms?

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. You can open the bags a little to let the water out if you see this so that the tubers stay in good shape. If your climate allows (read section “Timing”) you can plant the tubers as is. You can store your tubers or put them in pots to get a head start if you still have time before it’s safe to plant outside. 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 every so often to make sure that the bags aren’t getting wet and that the tubers aren’t drying out. If condensation starts to form, you can poke a hole in the bag or slightly open it to get the water out. If your potatoes are drying out too quickly, you can add a little water to the bags so that the shavings are just barely wet.

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”).

Dahlias do best in full sun, and they should be planted somewhere that gets at least 8 hours of sunlight every day. Dahlias planted in an area with less sunlight will grow taller and won’t yield as many blooms. If you live somewhere where it gets hot in the summer, dahlias will do best in a spot that gets some shade during the hottest parts of the day. Dahlias are heavy feeders and like soil with lots of organic matter. To keep tubers from going bad, make sure your soil isn’t too heavy and drains well. If it doesn’t, add peat moss or sand to make it better.

Dahlia tubers that are grown alone will clump together and multiply a lot over the course of the season, so make sure the soil is ready for this kind of growth. Start by digging a hole at least 8” wide and 12” deep. When we planted, we used an organic balanced fertilizer (you can find our secret mix here). But, depending on the results of your soil test, you may need to add more or less nutrients (nitrogen, phosphorous, potassium, etc.) to your soil. About 1/4 cup of the fertilizer should be mixed with some of the soil that you dug up before planting the tubers 4 to 6 inches apart, horizontally, with the eyes facing up. 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).

Once you plant your tubers, wait to water until you see the first shoots emerge. When you plant outside, the soil usually still has enough water in it for the tubers to start growing. If you are planting in a pot or the soil is dry, give the plants a good drink of water when you plant them, but don’t water them again until shoots appear. 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. Some types, like dinner plates, can take up to two months to sprout, while early-blooming types can take as little as two weeks.

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.

We amend our soil with an organic fertilizer mix at planting time. We use a fish and seaweed formula (low nitrogen) to feed the dahlias’ leaves every other week once they start to bloom. Since some of the nitrogen in our fertilizer is released slowly, we don’t give our plants more nitrogen-rich food once they start to bloom.

Growers of dahlias often pinch or “top” their plants to encourage growth along the sides and make the plant more balanced (not too heavy at the top). When the plant is about 12 inches tall, cut off the growing tip, leaving behind three to four pairs of leaves. If you do this, the plant will be more likely to send up low basal growth, which will not only give you more flowers to cut but also make the plant less likely to fall over in heavy rain or wind. Note: supporting your dahlia is paramount. If you are a home gardener, tomato cages or bamboo stakes work well. If you are growing a lot of plants, you should use tomato twine and T-posts spaced every 6 to 8 feet or “Hortonova” netting to keep them in line.

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 wont 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. For 3-5 days (the vase life of dahlias varies by variety and size), change the water and cut the stems again every day.

Harvest or deadhead dahlia plants regularly to promote additional flowering. Once flowers go to seed, the plants will slow down flower production.

It’s too cold to grow dahlia tubers in the Northeast in the winter, and the tubers will freeze if they are left in the ground. Every fall, tubers can be taken out, cleaned, and put away until next spring (see “Storing Dahlias” below for more information). Cut the dahlias close to the base, leaving about 6″ of stem to use as a handle to pull the tuber clump up after a hard frost has killed the plant. We can store our tubers better for the winter if we leave them in the ground for at least 10 to 14 days after a hard frost before digging them up. Waiting is not necessary, however, and tubers can be lifted the same day they are cut down. Take your time and do what works for you! Use a digging fork to carefully lift your tuber clump out of the ground, making sure not to break the tubers’ necks. Start at least 6″ away from the plant’s heart. We found that you have to “dig” around the plant two or three times to get the whole clump out.

Its 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. You might need to store your tubers in airtight containers with a packing medium (pet shavings, vermiculite, etc.) if you want to keep them somewhere dry. If your storage space is wetter (i. e. If you live in a wet area or an unfinished basement, you might have better luck leaving your tubers in an open box without any packing material. There is no single way for storage success. You will have to check on your tubers frequently/weekly to check for rot or shrivel. If the tubers have properly hardened off, they will stay firm in storage and not shrivel (because the storage area is too dry) or grow mold (because the storage area is too wet). Know that there is no “right” way to store tubers. The key is to maintain temperature and humidity.

Dahlia tubers are readily available from many growers online. Dahlia plants get their roots from tubers, which can be planted and will grow more plants 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!.

Dahlia 101 – Watering

FAQ

Do dahlias need water every day?

Do dahlias like to be wet or dry?

Can dahlias be overwatered?

How often should you water a dahlia plant?

If dry conditions do exist, water the tuber once and then wait for growth to occur. When considering dahlia watering, needs can vary greatly depending upon the growing conditions. Once the tuber has started to grow, consistent dahlia plant irrigation is required in order to promote lush growth and prolific bloom period.

How do you keep dahlias alive?

After harvesting, boil a pot of hot water. Make a fresh horizontal cut in your dahlia stem and dip your stems in hot water (water should no longer be boiling, but still hot). Dahlias have a hollow stem and this will help your dahlias to start drinking water and hopefully prolong their vase life.

Do dahlia plants need a lot of water?

Young dahlia plants do not need a lot of water; in fact, excessive water can lead to rotting of the plant. For larger plants, a good rule of thumb is to water if the rainfall is less than one inch in seven days. Pots require more regular watering.

How do you care for a dahlia plant?

When watering dahlia plants, always make sure to avoid wetting the plant foliage. This will help to decrease the likelihood of disease. Dahlia plant irrigation routines should focus on long and deep watering sessions. This process will promote stronger, studier plants and better root growth.