Dahlia Site Selection
- Choose a sunny, protected site free from heavy winds or potential of standing water. Dahlias are considered tender perennials. In zones 6 and colder tubers must be dug out in early fall to store for the winter. In zone 7, tubers may be left in-ground only in well-drained soils. They must be cut back and mulched over well to overwinter successfully, but colder than average winters may lead to some losses. Zone 8-11, cut back stems and mulch for winter.
- Soil for Dahlias should be well-drained and organically rich. Dahlias usually rot in heavy, wet soils.
- Plant from dormant, stored tubers in spring after any threat of frost has passed.
Note: In colder climates tubers may be started in pots indoors, to get a jump on the planting season. Start them approx. 6 weeks prior to the last average frost date. (Starting indoor instructions are below)
Dahlia Prep Instructions & Tuber Explanation
Dahlia tubers are bulbus storage roots. When fully mature they grow in a circular starfish-like pattern with several tubers attached to a central crown. When starting a new dahlia, mature plant roots are divided to separate tubers and the same but new plants will grow from a single, or several tubers.
It is important to understand that different dahlia cultivars will have different sized and shaped tubers. This is normal. They are all dahlias, but not all dahlias are the same, just like people or snowflakes. Some Dahlia variety tubers will be short & wide, while others may be long & thin. However, each tuber has a neck and crown. The eyes originate and grow from the crown at the tip of the neck.
In well-drained, organically amended soil prior to planting, incorporate ½ to 1 lb. of 3-5-3 Espoma® Bulb-Tone® or similar product into the bottom of each planting hole or apply at a rate of 2.5-3 lbs. per 100 sq. ft. for larger beds or planting areas.
Dahlia Planting Instructions
- Dig individual holes or simply dig a furrow for multiple tubers.
- Place tubers laying horizontally, 4-6 inches deep with eyes facing up.
- After planting, water just enough to moisten the soil.
Note: Know that eyes may be tiny and not visible at all. Don't worry, new shoots will self-right to grow upright.
- Larger tubers can be planted an inch or two deeper, up to 8 in. deep, but most growers will cover deeper planted tubers with only 3 in. of soil initially until new growth emerges, then keep adding amended soil as shoots gain height, until they are fully covered.
- Proper spacing is generally 1-2 ft. apart. Larger growing varieties benefit from wider spacing and smaller types can be slightly closer at 10-12 inches apart.
Note: Over-crowding can inhibit blooming.
TIP: Most of our Dahlias grow to a self-supporting size of 3 to 4 feet. If taller varieties are grown adding stakes at the time of planting may be needed. Put support stakes in near the crown end before covering the tubers to avoid accidentally spearing and scaring the tubers.
Starting Dahlias Indoors
- Start Dahlias about 6 weeks from desired planting out date.
- Use pots that are at least 18" deep and wide.
- Use a peat-based, fertilizer-free sterile potting mix with good drainage.
- Fill pots with about ½ pre-moistened mix, set tubers as you would in-ground and cover with only 2-3 inches of soil.
- Once shoots start to grow, add potting soil periodically as shoots gain size.
- Dahlia plants should be about 12 inches tall when you move them outside.
Note: Hardening off new plants for 7-10 days, is helpful to avoid acclimation or transition issues.
Pinching & Disbudding Dahlias
Pinching and disbudding are both important steps to the flowering success of Dahlias.
- Pinching is simple but necessary to create bushy, well-proportioned plants. The bushier the Dahlia the more flowers a plant has the capacity to produce. Pinching is the simple act of removing the center out of the stem. This is done once a young plant has produced 4-6 sets of leaves. As the plant matures, side shoots may also benefit from pinching as they grow. Pinching centers cause bushier plants from more branching lower in the plant.
- Disbudding is important to achieve the best and biggest blooms. Beginners are most likely to skip this step, where savvy growers who raise Dahlia flowers for Dahlia Society shows, State Fairs, or for florists know how essential proper disbudding is to produce large, perfectly formed flowers on long stems. Dahlias typically produce more blooms than a plant can support. Disbudding helps to focus the plants energy to only a select number of flowers. Like resources of a family with 2 kids vs one with 10 kids. With similar resources 2 kids are better off.
Disbudding is simple too. When the flower buds of the tip cluster are about the size of peas, remove all but one. At the same time, pinch out the small, tender growth buds below in the leaf axils of the next set of leaves on the stem. If you are cultivating a shorter bedding variety, you might also want to disbud from the next set of leaves after that. Obviously, for basic garden growing balancing the number of flower buds to the size of the plant will yield the best over-all appearance of the Dahlias.
Water sparingly at first to avoid over-watering and causing tubers to rot before they start growing. Once plants reach 6-10 inches tall regular watering using the 1 in. per plant per week rule is best during the rest of the growing season.
Dahlia Care - Maintenance After Establishment
General Care & Fertilizing
The biggest mistake many gardeners make with their dahlias is over feeding them. The point of growing Dahlias is to have flowers, however, to bloom well, Dahlias should be fertilized with a complete plant food that is low in nitrogen and higher in phosphorus. As with roses, vegetables, and other flowering plants the first number (N) should never be higher than the middle number (P) and the third number (K) will be like the first. Naturally derived, water-soluble fertilizers like Algoplus Flowering Plant (4-6-7) formula works well.
First applications should be within 30 days of planting and repeated approx. 3-4 weeks later. Avoid composts, manures, or Fish fertilizers, with high nitrogen. These nitrogen sources promote weak stems, little to no blooms, along with tubers that rot or shrivel in storage.
(See Pinching & Disbudding)
Cut Flowers - The best time to cut flowers is during cool mornings. For longest lasting blooms, place cut stems into 2-3" of hot water (approx. 160°-180°F) and allow them to cool at least one hour. This will set your blooms and help make flowers last for 4 - 6 days. Deadheading as needed will keep your plants strong and blooming late into the season.
Fall Digging - Fall digging commences after stems have died back from first hard frost. Using a spade or fork to plunge in and lift tubers judiciously working all the way around each plant. Make sure to start at least 1 ft. back from the center of the plant to avoid damaging tubers. Once you locate the tubers you can move closer.
- Tubers, necks, and crowns can be fragile and susceptible to breakage, so be careful.
- Lift tubers, brush off loose dirt and set in well-ventilated space out of direct sun to dry for a few days until any residual soil can easily be rubbed, wiped, or brushed off the tubers.
- Avoid using water, to clean tubers. Tubers must be as dry as possible to store successfully.
- Cull and toss out any tubers that are cut or damaged. They usually rot from fungal infection while in storage and can potentially corrupt other tubers.
- Before storing, separate clumps for new plants the next year. (See Dividing Tubers below) Make sure each tuber has a part of the stem with a neck and crown. To avoid mixing up varieties, label the tubers with an indelible pen at the time of digging.
Winter Storage - Use a storage medium such as peat moss, sand, or pet bedding material (sawdust or shavings). Tubers should be stored in crates or cardboard boxes. We recommend lining the containers with several sheets of newspaper. It is best not to stack tubers, but if you must, start with packing medium in the bottom. Alternate layering tubers with medium until the container is full.
Note: Never store in sealed plastic bags or bins, as these cause damaging condensation.
Store tubers in a cool, dry area (temps. of 40°-50°F is best). Too warm tubers can wrinkle/shrivel. Too cold and they can freeze, or too humid/wet tubers will rot. Check your tubers once a month throughout the winter storage months and adjust conditions as needed.
Dividing Tubers - Dividing is typically done in the fall prior to storing which allows for cut pieces to heal. Divisions can be done in the spring prior to replanting as well. Use sharp pruners or a knife to cut through the tubers. To prevent accidental fungal or bacterial infections, sterilize blades first with Lysol® spray, wipes or a 10% bleach & water dipping solution. The eyes will be located on the center stalk and each root must have at least one eye to grow. Not all tubers will have an eye. Removing a piece of crown with each tuber is the best way to assure they will have an eye, however, if you are unsure or cannot see any eyes, then only divide clumps into half or thirds. Again, cut surfaces should be allowed to dry overnight before planting or storing.