Dahlias require full sun (at least 8 hours daily) to thrive and
bloom abundantly. Southern growers might need to provide plants with
afternoon shade if summer temperatures are extreme. Dahlias are
cold-sensitive and should not be planted until the soil has warmed
to above 60°F (15°C) and all danger of frost has passed. Check with
your local county extension office to find out the date of your last
spring frost.
Select a sunny garden spot with freely draining soil, and prepare it
thoroughly before planting. Amend beds with 2 to 4 inches (5 to 10
cm) of high-quality compost or well-rotted manure, a light dusting
of bone meal, and a balanced organic fertilizer. Mix all ingredients
into the soil to distribute evenly.
To plant, dig a hole 4 to 6 inches (10 to 15 cm) deep and place the
tuber on its side, horizontally, with the growing eye facing up.
Once in place, refill the hole with soil. Dahlias get quite large,
so allow at least 12 to 18 inches (30 to 46 cm) of space between
plants.
Dahlias require consistent water throughout the growing season, so
install soaker hoses or drip irrigation while they are still young.
Dahlias should not be watered until you see the first green shoots
poking through the ground; overwatering before shoots are visible
can lead to tuber rot. After plants reach 1 foot (30 cm) tall, give
them a hard pinch by snipping out 3 to 4 inches (7 to 10 cm) of the
growing center to encourage low basal branching, which increases
flower production and overall stem length.
Slugs and snails damage young plants, and earwigs ruin the flowers.
Put down bait at planting time and periodically throughout the
season. Sluggo Plus is an organic option that’s safe for both
children and pets, and works well against all three pests.
By mid-summer, you’ll need to stake tall plants to keep them from
falling over. For home gardeners with just a few plants, place tall,
sturdy posts next to tubers at planting time so you can tie stems to
them as they grow. For flower farmers, I recommend the corral
method, which involves placing a metal T-post every 8 feet (2.4 m)
along the outside edges of the beds and stringing a double layer of
bailing twine from post to post.
While dahlias are not terribly long-lasting cut flowers, you can get
5 to 7 days from stems cut at the proper stage. Since dahlias don't
open much after they’ve been harvested, it’s important to pick them
almost fully open, but not overly ripe. Check the back of each
flower head, looking for firm and lush petals; papery or slightly
dehydrated petals are a sign of age. Be sure to use floral
preservative in the water.
