HOW TO GROW DAHLIAS

WHERE TO PLANT DAHLIA TUBERS

Dahlias will grow in almost any location and in almost any soil. However, to have outstanding plants and flowers, you must be selective of the planting placement. Dahlia roots need a sunny location in order to thrive. They should receive at least a half-day of sun and even more is preferable.

Select a site for your dahlia garden that is away from trees, sunny, and yet sheltered from direct wind. Dahlia tubers are surface feeders. Since they don’t send down a tap root or long feeder roots the plants will easily be blown over by the wind. Staking the plants is essential and will be covered later with planting instructions.

A further important consideration is the condition of the soil. In most cases, a good everyday garden soil is adequate. But good soil drainage is vital for dahlia plants. If the soil holds surface water for more than several hours after a rain, the likelihood is that it should be augmented with organic matter. Humus, peat moss, sand, or well-rotted manure will work well. A mixture of equal parts of all of the above makes an excellent addition to heavy soil.

HOW TO PREPARE THE DAHLIA GARDEN SOIL

If at all possible, choose the planting site in the fall. Dig or till your plot and start working in compost, peatmoss, sand, and rotted manure. Keep the site as weed free as possible during the winter months. This will make your spring work and planting much easier. Then as spring comes, the area will need a further digging, or tilling to a depth of at least six inches but eight to ten inches is better.

If you choose to use a commercial fertilizer, be sure to keep the nitrogen (the first of the three content numbers) to a low number. For example, a 5-20-20 would be adequate. This of course should be well worked into the area in a ratio of 3 to 5 pounds per 100 square feet. Further fertilization should not be needed although some people apply a second mid-season application of the above formula to their dahlias or use a similar ratio in a liquid form.

HOW TO STORE DAHLIA TUBERS

The storage of dahlia tubers prior to planting is critical. Tubers must not be allowed to freeze or to be placed in a room that is heated above 50 degrees F. A temperature of around 40 degrees F is preferred. The tubers must be stored in a dark location, high in humidity. A root cellar or basement with a dirt floor makes an excellent storage area. Continue to check your dahlia roots (tubers) weekly for rot or mould. As you handle the dahlia tubers be careful not to damage the growing point known as an ‘eye’. Remember, that is your future plant.

WHEN TO PLANT DAHLIA TUBERS

The dahlia tuber is unlike many other bulbs in that it wants to be planted in warm soil compared to say, tulips. A rule of thumb for planting time is: plant dahlias when you would plant other root type vegetables such as carrots. In other words, spring should be well on its way with the longer and warmer days.

PLANNING A DAHLIA GARDEN

Now that the area for planting your dahlia tubers is well prepared and your stock of tubers is in hand, it is time to prepare a garden layout plan. Because certain varieties grow considerably taller than others, you should plot where you want tall plants and where the shorter than average should go. Also, if color mass is important, then get these details laid out before you actually begin to plant. Many commercial dahlia suppliers indicate the approximate height of the plants in their catalogs. Using this information can be a help in formulating your layout plans.

The layout plan will also need to take into account the number of varieties that you plan to plant. The average planting space between plants is 18 to 24 inches, especially for the large flowering varieties. (Keep in mind that the size, such as AA or A, in "dahlia speak" refers to the size of the flower, not the size of the bush.) The shorter varieties can be planted closer together, but remember, when you dig those clumps in the fall, you definitely don’t want them intertwined with their neighbor!

Plan for the rows to be three to five feet apart, depending on the size of the plant. When the rows are two to three feet apart, the plants will generally grow taller as they ‘reach’ for light and your access up and down the rows becomes more difficult. Close planting also shuts down air circulation to the lower leaves, encouraging powdery mildew. If you plan to use a hand tiller between the rows, then plan your rows according to its width and be sure to leave extra width so as not to till too close to the plants and damage those new tubers.

TIPS FOR PLANTING THE DAHLIA TUBERS

Prepared holes for planting should be 5 to 6 inches deep. If you plan to stake the plants, NOW is the time to do this and not later when you may damage the tuber by running a stake through it. Pound a sturdy stake, 4 – 5 feet tall into the ground beside the tuber hole. Some have found tomato cages to be satisfactory in supporting the plants, but these too have wire spears and so they should be put in place when you can see exactly where the tuber is to be located. Tomato cages are generally only satisfactory for the smaller plants. With the stake or tomato cage in place and a planting hole on one or both sides of the stake, place the tuber in the hole laying longwise on its side, with the sprout or eye facing up. If the tuber has a sprout an inch long or more, care should be given not to damage the fragile shoot. However, if this does happen, and it is very easily done, then don’t despair, there are auxiliary eyes at the base of the broken shoot and they will grow, but you will have lost some advanced growth in your future plant. Do not add fertilizer to the hole as this may damage the new tender root system. Cover the tuber with 4-5 inches of dirt. Some gardeners have found it helpful to hill the plants as they grow to provide support to the stems, but often this is not adequate in wind prone areas. Tie a name-tag on your stake so you will know later which plant is growing there.

HOW TO WATER DAHLIAS

Unless it is a very dry spring, it should not be necessary to water at the time of planting. The tubers will begin growing with the warmth and moisture in the soil. It is vital that they form a root system early in their planted life to assure a strong and healthy plant. Watering at the time of planting may encourage rot causing you to wonder why that prized variety is not growing. When you carefully investigate the problem, you may not even be able to find the tuber or you will find a lump of rotten muck. Not a pretty sight!

Once the plant begins to grow you can begin to water every few days. Watering will be necessary in most areas throughout the summer months. Water dahlias at the root level using a drip system. Deep watering, or in other words, a good soaking is better than passing a spray on the plants for a short period. In fact, it is much preferred in order to prevent disease on the foliage and to conserve water. Many growers find the soaker hose in its various forms to be the best and then the water goes in the soil where the plant needs it.

HOW TO FIGHT DAHLIA PESTS

Once the shoot is above the soil surface, the first slug within a city block will ‘smell’ it. Be prepared!! Get out that slug bait and spread it liberally everywhere, or the slimy pests will devour every tender morsel for lunch! You may have other methods of taking care of these hungry critters, but I have found the slug pellets to be my favorite as I can broadcast them over an area very quickly and in most cases with good results.

MORE DAHLIA GROWING AND PLANTING HELP

Now that you have gone to all that work, you will want to care for your plants and see them produce beautiful prize-winning blooms.

Keep the area weed free, or at least as much as your back will tolerate. Also remove any broken or damaged foliage. Good air circulation, especially near the ground is needed by the plants to prevent powerdy mildew. Once the plants are several feet high the lower leaves can be removed to increase air circulation.

TYING DAHLIA PLANTS TO THE STAKES

When the plants get to be a foot tall, be sure to begin tying them to the stakes. A wind will lay your plants flat from here on and may even break the stalk from the tuber. (Then you will be sad!) You will need to continue to tie them to the stake every 18 to 24 inches. If you grow 4 or more plants of one variety, you may find it easy to run garden twine the full length of the row. This can easily be done down each side of the plants using the existing name stakes. The twine should be spaced every 8 – 10 " up the stake and can be secured on the stakes just with a single wrap around each stake as you go down each side of the row. This fast method works well until your housemate snips the string while cutting a bouquet of flowers. 

DAHLIA CLUBS

If you are growing dahlias for personal enjoyment or for show purposes, you will find it helpful to locate and become involved in a local dahlia club. A dahlia club is the best place to learn the art of showing and growing dahlias. Contact the following resources:

American Dahlia Society
c/o Alan Fisher
1 Rock Falls Ct
Rockville, MD 20854

Colorado Dahlia Society
www.dahlias.net

Puget Sound Dahlia Association

"Dahlias of Today" publication
Steve and Sandy Boley
12027 62nd Avenue South
Seattle, WA 98178
e-mail: sbgseattle@aol.com

Any questions: please email us, phone 503-662-3951 or fax: 503-662-4952.