How To Grow Dahlias 101
ABOUT DAHLIAS:
Dahlias are gorgeous flowers that grow best in well drained soil with plenty of sunlight (6+ hours a day). They are considered perennials in USDA hardiness zones 8-11, but usually need to be grown as annuals in any zones below zone 8 (you can find your hardiness zone here: https://planthardiness.ars.usda.gov/PHZMWeb/). They will not survive freezing, and therefore need to either be dug up from the soil before winter OR you will need to purchase new ones each spring to replant. Dahlias can be planted from seeds, cuttings, or tubers. Usually, they are grown from tubers, which multiply underground each year while the plant grows. Dahlias grown from seed may not be true to type (due to cross pollination), which is why most people plant tubers, since tubers will be exact copies of their parent plants.
It’s pretty crazy that these strange, potato-like things (tubers) grow into such gorgeous flowers! Don’t be surprised if your tubers look a little (or really) ugly when you receive them, just have faith and know they will turn into beautiful beings soon. When it comes to tubers, size doesn’t matter! Some varieties produce very small tubers, while others produce large tubers. Tubers produce “eyes” (like a potato) on the crown portion which will grow into plants. Every tuber we sell is guaranteed to have at least one (if not many!) viable eye that will grow into big, healthy plants.
RECEIVING YOUR TUBERS
We sell dahlia tubers every year between February and March (shipped in April). f you purchase tubers from us: when you receive your dahlia tubers, open the box and bags IMMEDIATELY. Store the tubers in a cool place between 41-50*F until you are ready to plant them. To prevent tubers from drying, pack them in peat, sawdust, or vermiculite in newspaper, paper bags, or plastic. Do not leave them in closed plastic bags, as they may produce heat causing the bag to condensate - which in turn, may cause excess moisture and can cause the tuber to mold or rot. Do not store them too wet.
SOIL
Plant in well-balanced, well draining soil. Generally, dahlias do great in plain old “dirt,” and there is usually no need to add lots of amendments. The best way to determine if your soil is balanced is to get a soil test. Be sure that you plant in a spot that has lots of available phosphorus, and does not have excess nitrogen. Excess nitrogen in the soil will cause dahlia plants to grow big but will produce very few (if any) flowers. A soil test isn’t absolutely necessary for home gardeners, but it definitely helps to know what’s going on in your ground and it can help immensely in troubleshooting plant problems. A soil test will also tell you if you need to fertilize or not (we generally don’t fertilize much on our farm since our soil is well-balanced).
PLANTING DAHLIA TUBERS
When you receive your tubers, take them out of the box immediately. If you dug and overwintered dahlias from the previous season, take your tubers out from storage when spring arrives. During storage, tubers may have become slightly shriveled, have a small amount of mold on them, or may have even starting growing! This is all normal, so don’t panic. Sometimes during shipping in a warm environment, the humidity can makes tubers grow a small amount of mold in a very short amount of time (12 hours or less!). Simply brush off any mold and keep in a cool, dry spot until planting. Plant your tubers well after any chance of frost, when soil temperatures are at least 60 degrees Fahrenheit (Here in central New York state, in hardiness zones 5/6, we usually plant ours the second week of May). Plant tubers 4-6” deep, and 12-18” apart in well-draining, moist (not wet) soil with plenty of organic matter. Simply lay tubers on their sides in the hole you dig for them. Alternatively, you can also plant them in large pots (5 or 7 gallon sized pots). Dahlias prefer to be planted in a spot that receives sunlight at least 75% of the day or more. When first planted, water VERY sparingly, or not at all, depending on soil conditions. You want the soil to be slightly moist, but not wet (if you take a handful of soil and squeeze it, you should not see any water drip out). If tubers get too much water before they sprout, they have a tendency to rot in the ground. Depending on the variety, you will begin to see sprouts emerge from the soil in 3 to 8 weeks (you have to be patient with some varieties!).
GROWING DAHLIA PLANTS
Once plants reach about 6” tall, give them plenty of water as they love to drink now, and risk for rotting has passed. To get bushier plants and lots of blooms, pinch back your plants at about 12” tall (simply cut off the top third of the plant). I know this sounds cruel, and it will delay flowering for a few weeks, but it will reward you will tons more blooms. Be sure to also properly support your dahlia plants with stakes or a tomato cage, as the plants can get huge- some of ours get over 5’ tall! After about 12-16 weeks, your plants will start to produce flowers (yay!). Most years, most varieties are flowering by mid to late August, but other years when the weather isn’t ideal it can take them longer to bloom. Some varieties may not bloom until September or later, dependent on the weather.
HARVESTING DAHLIA FLOWERS
If you plan to cut your dahlia flowers and bring them inside, cut them early in the morning when it is cool. If you cut them in the middle of the day they will not last as long. Be sure to cut them when the flowers are almost fully open, but not overly ripe. The optimal cutting stage varies slightly between varieties, but this is the general rule of thumb. You can expect anywhere from a 3 to 7 day vase life (variety dependent). To extend the vase life, use super clean vases (bleach is your friend here), trim the stems often and change the water daily. Flower food helps, too.
DIGGING DAHLIA TUBERS
In most cold climates, dahlia tubers can’t survive the winter. There is a chance they can survive with good mulching and plenty of protection, but generally in NY state this isn’t done successfully. We don’t take the risk at our farm, so we dig ours up every year, right after the first frost in the fall (usually late October). Over the past year, your dahlia tuber will have multiplied underground. I am always amazed at how much they grow in one season! We wait to dig until we get a killing frost, but you can do it earlier. When digging, we like to cut back the foliage to about 4-6” tall. We use the stem stubs as a “handle” to help get them out of the ground. Simply use a spade or shovel to gently loosen the soil around the tuber clump and gently lift from the ground. When digging, be very careful not to damage the tubers, as the tuber clump will be much larger than the one you planted in spring. You can either store “as-is” with the soil on, or you can rinse off any soil stuck to the clump and allow the tubers to dry, then store again for the winter.
ALTERNATIVELY: DON”T DIG THEM AT ALL! Quite frankly, it’s a lot of work to dig up dahlia tubers in the fall. For the minimal cost of dahlia tubers, it’s worth it to many people just to leave your tubers in the ground and purchase new tubers every spring. The added advantage to this is that you can try out new and different fun varieties every year, so you’ll never grow old of the same varieties (although, I don’t know how you could ever get sick of looking at any type of dahlia!).
DAHLIA TUBER WINTER STORAGE
Dahlia tubers need to be stored in a cool, high humidity environment through the winter months. It is important that they stay cool, but don’t freeze. Ideal home storage temperatures are between 40 and 50 degrees Fahrenheit. There are many different methods you can use to store your tubers. You can pack them in peat moss or wood shavings in plastic bags or totes. The goal is to minimize air flow to the tubers. You can also wrap individual tubers in plastic wrap. Either way you store them, it is important that you check on the tubers often throughout the winter. If the environment is too humid and the tubers become too wet, they may rot. If the environment is too dry, the tubers may dehydrate and shrivel up. Ideal tubers should be firm and plump, although minor shriveling is fine.
Happy gardening!