Read an Excerpt
A major factor in growing dahlias successfully is the treatment of the tubers. Tubers that are grown, dug, and stored properly will produce healthy, vigorous plants when replanted.
After the dahlia plant has completed its full growth cycle, it goes dormant. In warm climates the dormancy period can be as short as a few months, and tubers may be left in the ground. In areas where the ground freezes the tubers need to be dug and stored. Dahlia growers often find it difficult to keep tubers viable during long storage. Understanding the correct methods of caring for tubers can simplify the task.
Dahlias will tolerate a wide range of soil types and pH levels; however, the healthiest tubers are produced when the plants are grown in a nutrient-rich and organically healthy soil. Compost, organic fertilizer, and humus should be added yearly to maintain soil viability and optimize tuber health and production.
In warm, frost-free climates, tubers may be planted at any time of the year. In climates where it freezes, plant tubers after the danger of frost has passed. Place tubers in the ground 1 to 3 ft. (0.3 to 0.9 m) apart, depending on the size of the plant. The space around each plant needs to be adequate for good air circulation; air movement will keep the plant leaves dry, which helps to discourage airborne plant diseases.
Your garden soil type determines the depth to plant the tubers. The depth of the tuber will depend on the soil structure and temperatures. Sandy soil and high temperatures may require depths of 3 to 4 in. (7.5 to 10 cm); heavy soils with low temperatures, depths of 2 to 3 in. (5 to 7.5 cm). Soil temperature needs to be 50 to 80°F (10 to 27°C) in order for the tuber to break its dormancy and begin growing. If the soil temperature is too cold and wet, tubers can disintegrate. If the soil temperature is too warm, the tubers break down and will not grow. Mark your plantings with tags or stakes so they can be easily identified at digging time.
Dahlias can be propagated from cuttings. The tubers produced from a cutting will keep well in storage, often better than tubers produced by a plant. The number and form of tubers produced from cuttings depends on the method of planting the cuttings. When planted upright, they will seldom produce more than two misshapen tubers with viable eyes. To increase tuber production and improve the form, let the cutting grow to 8 to 10 in. (20 to 25 cm). Lay the plant horizontally in a 3 in. (7.5 cm) trench, and then cover the roots and cutting to the top set of leaves. As the plant grows it will develop three to five perfectly shaped tubers at each node.
A dahlia plant needs a minimum of three months' growth to develop mature tubers. The feeder root system is shallow on the dahlia plant; deep cultivation can cause root damage and should be avoided. During the growing season, a thorough weed-control program is essential. Dahlias also need consistent watering and fertilizing for healthy tuber production. During the bloom season all spent blooms should be removed, which will increase nutrients to the tuber. Several weeks before digging the tubers, discontinue watering and fertilizing so the tuber growth will slow and tubers will begin hardening-off in preparation for harvest.
Dahlia tubers will be destroyed if they are allowed to freeze so in certain areas they will need to be dug each year. In the short days of fall, the plant's flowers will lose their form and have open centers. The plant will develop weak stems and start setting seed. This is an indication the plants are going into dormancy. The tubers can be dug at any time. After frost the eyes will develop on the tubers and make the tubers easier to divide.
If there is a chance the ground will freeze, leave the frosted tops on the plants until they are dug to help protect the soil and tubers from freezing. Before digging the tubers, remove all ties and stakes. Check the labels on the tags for correct identification. Cut the top growth from the plant leaving 4 to 6 in. (10 to 15 cm) of stem attached to the base of the plant. This short piece of stalk will give you a convenient place to attach identification tags and it will provide a means for handling the dahlia clump. Use a shovel or digging fork to carefully loosen the soil around the tuber clump and then gently lift it from the ground. Always handle dahlia clumps carefully to avoid breaking the fragile necks on the tubers. Finally, wash all soil from the clump, using a forceful spray of water. The force of the spray should be sufficient to remove all the soil from the clump of tubers; however, it should not be so forceful that the thin protective "skin" that covers the outside of the tubers is damaged.
It is important to divide the tuber clumps and get them in storage as soon as possible. In very dry climates, where the humidity is less than 50%, the tubers should be kept moist while you work to divide them. If the humidity is high, the tubers can be allowed to air dry in the shade. Some growers successfully dig and store the tuber clumps without dividing. Many growers dig only what they can divide and store in the same day. Both methods have advantages. If the clumps are not divided until spring, it is easier to see the new growth, which greatly aids in division. Undivided clumps require considerably more storage space than clumps that have been divided.
Dahlia clumps can be divided and separated into individual tubers with knives, long-nosed clippers, saws, or any tool that will remove the tuber from the clump. Tools used for dividing the tuber clump must be sharp in order to make a clean cut. To help prevent injury, wear rubber or latex gloves and work under adequate light. The long-nosed clipper is an especially safe tool.
Before dividing the tubers, remove any damaged tubers, all root hairs, and any tubers smaller than a pencil in diameter. Leave only the trimmed tubers on the clump. When you divide the clump each tuber must have a viable eye. The eyes are located near the stem of the clump. It is necessary to have an eye on each tuber for new growth to develop the following year. For the first cut, divide the clump into two parts. It is now possible to separate each tuber from the divisions, each with a viable eye. Remove as much of the stem as possible from each tuber. It may be necessary to leave two or three tubers attached in order to keep an intact eye.
As soon as the tubers are divided, identify each one somehow (by name, numerically) with a permanent indelible marker. When marking many tubers of one variety, a rubber stamp kit will speed up the process. Some growers dip their tubers in fungicide or a weak bleach solution before storage; however, no research proves the benefit of such a dipping.
