How To Grow Dahlias

It is Important to understand that dahlias grow from tubers and are not bulbs. Bulbs such as lilies, daffodils, and tulips can be planted in wet, cold soils in the fall. Dahlias must be planted in warm, well-drained soils at springtime. Dahlias are generally planted at the same time you would plant your vegetable garden during April or May after all danger of frost has passed.

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 no 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 will be sparse and weak headed.

Soil Preparation

Prepare your beds a few weeks before planting. Beds should be well drained and in an open, sunny location. Use aged steer manure, compost, or a 10-10-10 fertilizer spread evenly over the bed, then till it in. If you have a heavier soil, work in sand or peat moss to lighten the texture of the soil for better drainage. Bone meal is ideal used at planting time. Put a small handful in the hole and work in well before planting each tuber.

Planting

Ground should be warm and well drained at planting. Do not use bark dust or compost containing bark on beds where you plan to plant dahlias. Bark dust does not allow the sun to warm the soil properly and the tubers will not sprout as they should. Bark also increases the soil acidity, which is harmful to the dahlias. Lay the tuber horizontally at a planting depth of 4”-6” inches and about 18” to 24” inches apart, then cover with soil. For a quicker start, plan the tubers 3” to 4” inches deep and then “hill up” soil after plants are up and growing. Hilling to a depth of about 8 inches will help support the plant. Stakes should be put in at the time of planting to avoid damaging the tubers at a later date. Do not water tubers after planting. The spring soil has enough moisture to promote proper growth and the spring rains will provide enough water. In case of an extremely wet spring, you may delay planting until dryer weather prevails.   Planting times are generally Mid-April thru May for most Climates, but are planted in March in warmer southern states. If you are planting in deck container 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 soil damp may result in rotting tubers in the pot.

Watering

Most areas have enough rains to fill water needs at first. We do not recommend watering until sprouts are at least 4” – 6” inches above the ground. We plant in April in our area and do not water until about the end of May when the shoots are at least that tall. 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 per week is necessary during warmer, dryer weather or in hotter climates. Proper watering will promote better blooms.

Fertilizing

One of the biggest mistakes made with dahlias is over feeding them. You can love them to death! Do not over fertilize, and stop fertilizing a couple of months before the plants go dormant. Then, the tubers have time to harden-off and remain strong in winter storage. We recommend a balanced fertilizer with equal parts Nitrogen, Potassium and Phosphorous Fertilizer such as 5-5-5 or 10-10-10. These can be found as vegetable fertilizers at your local garden centers. They should be applied within 30 days of planting and can be repeated at about 6 week intervals, but we apply it only once in our field. If using a stronger (higher number) fertilizer, use less. It’s better to feed them too little, then too much. Stop feeding plants by the end of August. Potassium and phosphorous break down slowly and will become available to your plants during peak blooming. Always check your fertilizer labels for nitrogen amounts when buying fertilizers for dahlias. Nitrogen percentage is always the first number listed on the package, and should not exceed the other two numbers. Consider using compost tea and earthworm tea or castings, which have been successful for us and are great for soil health.

Weed Control

Recently products have become available that claim to control weeds without affecting the growth of flowers. It is our experience that these products do have a negative impact on dahlias. Do not use commercial week killers where you are going to plant dahlias. Old fashioned hand weeding is still the best remedy for weeds. Dahlias have roots near the surface. Avoid mechanical weeding methods, which can damage the root system.

Pest Management

Snails and slugs eat the tender shoots as they try to break through the ground in spring. Use snail bait to prevent these pests from eating up your tender plants. To control other pests, a good spring spraying program is recommended. Most spray programs should begin before you see a problem, preferably the end of June thru August. There are a variety of products on the market. Look for products to control earwigs, cucumber beetle, and spider mites. Check the labels to ensure each is safe for your environment, pets, and beneficial insects. Spray in the early morning or late evening to prevent hurting your local bee population. Be sure to spray the top and undersides of plant leaves.

Powdery Mildew

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 Plant Therapy, but your garden store may have other brands that work just as well. The key is to spray before the problem appears, as it can be difficult to eradicate once it gets established.

Topping

To promote shorter, bushier plants with better stems for cutting, we advise pinching or cutting out the center shoot when the plant is about 12 inches tall.

Cut Flowers

After cutting your blooms, place cut stems in a clean container with clean water and flower food. Cut dahlias are susceptible to bacteria and will last longer if their water is changed and stems are trimmed. Be sure to remove the old, spent blooms from your plants. Removing old blooms (dead heading) will keep the plant strong and vigorous late into the season. Also, it encourages new blooms and better bloom color throughout the season.

Digging

Optional if the ground doesn’t freeze. Dig dahlias about 2 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. Tubers dug before a frost may be “green” and shrivel badly or rot in winter storage. If your area has not had a hard frost by mid-November, it is okay to dig by them out. The cool nights will slow down the 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 tuber 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).

Dividing

You can divide tubers in the fall or in the spring. If you have never divided tubers before, spring is best as it is easier 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. Cut surfaces should be allowed to dry thoroughly overnight before storing (in fall), or planting (in spring). Tuber size does not affect plant growth. The smallest tuber will produce a full sized plant if it has an eye. Different dahlias produce varying size and shapes of tubers.

Storage

There are many ways to store tubers. We pack our divided tubers in pet bedding (wood shavings) and paper bags. Then, keep them in open bulb crates, and check and rotate them regularly to ensure they are not molding or drying out. Another option is to pack tubers in crates or cardboard boxes that have been lined with 9 – 10 sections of newspaper with a storage medium of sand, peat moss, dry sawdust, or pet bedding, etc to help prevent tubers from shriveling or rotting. Never store roots in sealed plastic bags, as they will rot. A cool, dry area is preferred to store tubers over winter (temp. of 40 – 50 degrees is ideal). Beware if a cool area may be susceptible to freezing. If the dahlia tubers are exposed to temperatures below 32 degrees, they will die. Bulbs such as daffodils, tulips or lilies can survive below 32 degrees. Dahlia tubers cannot. Check the tubers several times during the winter months to see how they are doing. Remember, there are no absolute rules to storing dahlias. Experiment to find a variation of the above method that works best for your climate.

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