It is important to understand dahlias grow from tubers and are not bulbs. Dahlias must be planted in warm, well-drained soils at springtime. Dahlias are generally planted about the same time you would plant your vegetable garden.
SELECTING A SITE: Dahlias need a sunny location to thrive. An area that receives at least 8 hours of direct sunlight is best. Hot climates are an exception to this, as dahlias should be planted where they will receive morning sunlight, but not hot afternoon sun. No matter what climate you have, do not plant in areas that are shaded all day. If you do, the plants will be tall and spindly, blooms are weak headed, and blooming is sparse. Do not plant in areas, or beds that have been chemically treated for weeds, or weed control.
SOIL PREPARATION: prepare your beds a few weeks before planting. Beds should be well drained and in an open, sunny location. Use a good steer manure or a commercial 5-10-10 fertilizer and spread it over the bed, then till it in. If you have a heavier soil, work in sand or peat moss to lighten and loosen the texture of the soil for better drainage.
PLANTING: Ground should be warm and well drained at planting. Do not use bark dust on beds you have planted dahlias in. Bark dust does not allow the sun to warm the soil properly and tubers will not sprout, as they should. Bark dust also increases soil acidity which is harmful to the dahlias. Lay the tuber horizontally at a planting depth of 6" and about 18" to 24" apart then cover. For a quicker start, plant tubers 3 to 4 inches deep and then hill up after plants are up and growing. Hilling to a depth of about 8 inches will help support the plant. If you plan on staking your dahlias, stakes should be put in at the time of planting to avoid damaging tubers when trying to put stakes in at a later date. Many customers have had excellent success with tomato cages instead of wood stakes. As the plant grows through the cage, you don’t see the cage and the plant are well supported. Planting as the spring soil has enough moisture to promote proper growth and the spring rains will provide enough water. NOTE: in case of extremely wet spring, you may delay planting until dryer weather prevails. Planting times are generally April through May for most climates, but are planted in March in warmer southern states. If you are planting in DECK CONTAINERS OR POTS we recommend using garden soil, or a mixture of 2 parts garden soil and 1 part potting soil. Dahlias planted in 100% potting soil will dry out too often causing poor bud formation. Over watering to keep potting soil damp may result in rotting tubers in pot.
WATERING: Most areas have enough rains to fill water needs at first. We do not recommend watering until sprouts begin to appear above the ground. This gives the tubers a chance to form roots, which can absorb water. Watering too early will increase the chance of rotting tubers. After plants are established, a deep watering once or twice a week is necessary during warmer, dryer weather or in hotter climates. Proper watering will promote better blooming. Fertilizing A high percentage potassium and phosphorous fertilizer such as 0-20-20 to 10-20-20, 5-10-10 should be applied within 30 days planting. Low nitrogen fertilizers can usually be found at your local garden centers. Potassium and phosphorous break down slowly and will become available to your plants during peak blooming. High nitrogen fertilizers are to be avoided as they promote weak stems, small blooms and tubers that rot easily during winter storage. Always check the labels for nitrogen amounts when buying fertilizers for dahlias. Nitrogen percentage is the first number listed on the label.
PESTS: Snails and slugs eat the tender shoots as they try to break through the ground in spring. USE SLUG BAIT to prevent these pests from eating up the tender new shoots. To control other pests good spraying program is recommended. ORTHENE and ORTHENEX work well to control most insects. SEVIN is best for earwigs and cucumber beetle. Orthene is excellent for spider mites, which thrive in hot weather. Be sure to spray top and undersides of plant leaves. Most spray programs should begin before you see a problem, preferably the end of June through August. Dahlias are also susceptible to powdery mildew. This is not caused by overhead watering. It is caused by weather conditions. Dahlias should be sprayed in July and August for powdery mildew. We use CLEARYS, but your garden store may have other brands that work just as well. The key is to spray before the problem appears.
CUT FLOWERS: After cutting your blooms, place cut stems in 2 - 3" of VERY HOT WATER (approx. 160 degrees) and allow to cool for one or two hours. This will "set" the blooms and make your arrangements last for 4 to 6 days. If you do not cut the fresh flowers from your plants, be sure to remove the old blooms. Removing old blooms will keep the plant strong and vigorous late in the season. Also removing old blooms encourages continued blooming and better bloom color throughout the season.
DIGGING: Dig dahlias about 1 weeks after a hard frost, the plants will turn brown when frosted hard enough. This allows time for the tubers to "cure" under the ground before you dig. "Cured" tubers shrivel less in storage. If your area has not had a hard frost by Mid November, it will be safe to dig by then as the cool nights will slow down plant growth and tubers will "cure". Cut the stock off to about 6" then gently lift the tubers from the soil with a spade or pitchfork being careful not to break the necks. Wash dirt from the roots with a garden hose and allow to air dry (NOT IN DIRECT SUN) in a protected area only as long as it takes the skin surfaces to dry (usually overnight).
STORAGE: Pack tubers in crates.. Use a storage medium of sand, peat moss, etc. to help prevent tubers from shriveling. Never store roots in sealed plastic bags as they rot. A cool, dry area is preferred to keep tubers in over winter (temp. of 40 to 45 degrees is ideal (After 40 to45 degrees). Beware a cool area may be susceptible to freezing. If the dahlia tubers are exposed to temperatures of 32 degrees or lower, they will be ruined. It is a good idea to check the tubers several times during the winter months to see how They are doing. REMEMBER THERE ARE NO ABSOLUTE RULES TO STORING DAHLIAS. You may also use plastic bags along with course vermiculite to absorb any moisture.
DIVIDING: You can divide tubers in the fall or in the spring. If you ha never divided before, spring is best as it is the easiest time to see the eyes when the new sprouts form. If eyes are difficult to see, we suggest dividing the clump in half, or quarters. Not all tubers will have an eye. (See illustration) Cut surfaces should be allowed to dry thoroughly overnight before storing, or planting if spring dividing. Tuber size not affect plant growth so even the smallest tuber will produce a full size plant if it has a live eye. Different varieties produce different size and shape tubers.