Dahlia

Full sun with moisture retentive but well drained soil. Use compost and bone meal at planting, and add pumice if the tubers will stay in the ground over winter. Water about 1” once a week in early summer and fall, and twice a week through the hottest part of summer.

Despite being natives of Mexico, Dahlias do not appreciate hot, dry weather. In the wild, they are found in foothills where the temperature is always moderate and summer rains are frequent. These are the conditions we must strive for when growing dahlias.

When we plant tubers or start plants in spring, the soil is cooler and wetter than ideal. If planting tubers, do not water on planting and wait for them to sprout.

The best time to drive a sturdy stake—appropriate to the expected height of the dahlia in the ground nearby—is at planting.

Dahlias respond best to low nitrogen fertilizers, such as bone meal or bulb food, at planting and perhaps once more during the summer. Giving low nitrogen fertilizers will encourage blooming without promoting excess growth.

Little maintenance is required for dahlias to be the stars of the late summer and fall border. However, a little extra attention will definitely pay off. If one is to keep maintenance to a minimum, then some care should be taken at planting time (see planting instructions in the culture section).

If planted as indicated above, annual maintenance will only require watering deeply once a week (maybe twice if it’s particularly hot) and cutting plants to the ground when frost kills the top in the fall.

Cutting flowers when fully bloomed will help direct energy into the formation of new flowers, in addition to providing a beautiful bouquet to display that will last 40-6 days in water. Keep in mind, scalding tips of stems in hot water (180 degrees) will help the cut flower last a bit longer. Deadheading spent flowers will also spur new blooms!

Digging, storing, and dividing is optional—but all can prolong the life of plants, enhance their flowering, and ensure their survival through the winter. When frost kills the top of the plant, or on November 15th if we still haven’t had a frost, cut the plant roughly 6” above the soil surface and carefully dig up the tubers.

Remove as much soil as you can from the tuber, then put it in a place where there is good airflow and protection from potential rain (such as a covered porch). Leave it there for 2 days or until the outer surface is dry to the touch. For storage, place tubers into cardboard boxes with shaved wood animal bedding or peat moss on all sides.

Store your tubers in the coldest possible place they can be without freezing. If they freeze, they will die. Around May 15th, remove the tubers from storage and look for the eyes, which range from little pink or green bumps to obvious sprouts which are starting to form. The dahlia can be divided into as many pieces as there are eyes. The most vigorous plants will come from the eyes with the largest tuber still attached.

Dahlias can also be propagated by cuttings, the most effective ones are taken when the sprouts are 2-3” tall.

Dahlias produce viable seed if you don’t deadhead them. If more than one dahlia is present, seedlings will be different from both parents. Again, do not deadhead if you want to save seeds. Wait for the spent flower head to change from green to straw-yellow, then peel back the outer sepals and look for seeds near the base.

Slugs and snails love dahlias. Starting in mid-May, apply Sluggo or set out beer traps near new plants and tubers left in the ground. Once the plants are up and growing, damage is usually minimal.