All You've Ever Wanted to Know About Dahlias

Do you love the way dahlias look, but you’re not quite sure about what it takes to grow these beautiful blooms in your own garden? Find out all you’ve ever wanted to know about dahlias in this post.

There are so many reasons why dahlias are my favorite flower. They’re not only available in a rainbow of colors, but there are so many varieties to pick from, and different shapes and sizes. Dahlias take their time to fully bloom, but they are so worth the wait! You’ll find them in the garden from mid-summer through fall’s first freeze. I think what I like best about dahlias is the fact that they peak at a time when other flowers in the garden are starting to die off.

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GROWING DAHLIAS IN DIFFERENT CLIMATES

Dahlias are considered a tender perennial in cold regions of North America. They are only winter hardy in planting zones 8 to 11. I’m in zone 8 here in the Seattle area, so I am able to keep my tubers in the ground year round. However, I make sure to put mulch or mowed up leaves around each plant for added protection during the winter months. Gardeners in zones 2 to 7 should plant dahlia tubers in the spring, and either treat them as annuals, or dig them up and store them through the winter.

SOIL REQUIREMENTS

Pick a spot in the garden with freely draining soil, and prepare it thoroughly before planting. According to Floret Flowers, you should 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.

WHEN TO PLANT

Dahlias are cold sensitive, so when you plant your tubers in the spring, do not do so until the ground temperature reaches 60°F, and there is no more chance of frost. To get a head start on the growing season, some gardeners start tubers indoors and in individual containers a month before they would plant them in the ground. I tried this, but for the amount of work it took, I did not see huge results. But that’s just me.

WHERE TO PLANT

Dahlias require 6-8 hours of full sun a day in order to thrive. If you are growing dahlias in the southern part of the country, you will most likely need to provide afternoon shade from the extreme temperatures.

HOW TO PLANT

Dig a hole 4-6 inches (10-15 cm) deep and lay the tuber on its side, horizontally, with the growing eye facing up. Fill the hole with soil. Space the tubers between 12-18 inches (30-46 cm).

WATERING

It’s important not to water your newly planted tubers until you see the first green shoots coming up through the ground. Watering before any new growth is visible can cause the tubers to rot. Dahlias love being watered consistently through the growing season. After your dahlias are established, you should water your plants deeply 2-3 times a week for at least 30 minutes. I have a drip system which works really well. You will need to give your plant more water in hot and dryer climates.

PINCHING

After the dahlia plant reaches about 1 foot (30 cm) tall, give them a hard pinch by snipping out 3-4 inches (7-10 cm) of the growing center branch. This will encourage bushier plants, as well as increase flower production and overall stem length.

PEST AND DISEASE CONTROL

Slugs and snails LOVE young dahlia plants, and earwigs ruin the flowers. Put down slug bait not only after planting the tubers, but also throughout the season. There have been times when I have forgotten to put slug bait down around my new dahlia plants, and the slugs enjoyed eating the entire thing. I use Sluggo, which is an organic option that’s safe for both children and pets, and works well against all three pests.

Powdery mildew has shown up on my dahlia leaves every fall. You can proactively spray for this in late July to August to prevent this issue.

STAKING

You will need to stake your dahlia plants when they are a couple of feet tall to keep them from falling over and snapping the stems. In areas that I have many dahlias planted in a row, I use the corral method. I learned this from Floret Farms. This method 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.

DEADHEADING

Deadheading is basically removing the spent flower heads. To get continual flowering throughout the season, deadheading needs to be constantly done. It prompts the plant to produce more flowers. Cut back just above the point where the flower stem joins a main stem.

HARVESTING

The more you cut dahlias, the more blooms you will have from your plant. Make sure you’re harvesting in the early morning, before the heat of the day. Place the cut flowers in a bucket of cool water as you are cutting from the garden. Be sure to remove all leaves from the stems and place the dahlias in a vase of water. Be sure to use floral preservative in the water. Since dahlias don’t open much after they’ve been harvested, it’s important to pick them almost fully open, but not overly ripe. Don’t select a flower for your arrangement if the back of the flower head looks like the petals are browning and dehydrated. The flowers should last anywhere from 5-7 days if properly taken care of.

WINTER CARE AND STORAGE

SHOULD YOU LEAVE IN THE GROUND OR DIG UP AND STORE?

Dahlia plants will blacken after the first fall frost. Once this happens, cut all but 1-4 inches off the plant. Dahlias are hardy to Zone 8, and can be cut back and left in the ground to overwinter. I spread mulch or mowed up leaves around the plant to add protection. In most areas, the winters are too cold to leave the tubers in the ground. For other zones that have colder winters, the tubers should be carefully dug up with a pitchfork or shovel in late fall before the hard frost, and stored through the winter. Be careful not to damage them.

DIVIDING

It is a good idea to divide dahlias every year because of how quickly the tubers grow. If they get too large, they will rot or become too heavy to lift and store. Trust me, I have experienced this problem! Once the clumps have dried, split them in half with sharp pruners so the pieces are easier to work with. After that, you can divide these tubers into individual tubers. In order for a tuber to be viable, the eye or eyes must be connected to an unbroken tuber.

STORING DAHLIA TUBERS

After dividing, wash the clumps to remove all the excess soil. Then dip the clumps into a 5% bleach-95% water solution and lay them out to dry in a cool place, such as a basement or garage for a couple of days. Once the dahlia tubers are dry, pack them in slightly dampened peat moss or sawdust, and then in a box lined with newspaper. You can also individually wrap them individually in pieces or plastic cling wrap. Store them in a well-ventilated, frost-free place, from 40-45º F is ideal, 35-50º. Try to keep the tubers from touching each other, in case one of them rots. Check them monthly, throughout the winter, and dispose of any that have started to rot.

IN THE SPRING

There are two scenarios here. I leave my tubers in the ground all winter. So usually in April, I dig up the clumps of tubers, and do my splitting at that time. If you have stored the tubers for the winter, then you have most likely already divided the tubers before storing them away for the winter. Remember that each tuber must have at least one eye, or the tuber will not bloom. The eyes are located at the base of the stem and look like little pink bumps.

I hope that this covers just about all you’ve ever wanted to know about dahlias. Yes, this gorgeous flower does have a bit of work involved such as dividing, storing and staking. But you will not find a more beautiful flower that produces so many blooms. I would love to hear if you have any other tips or ideas. What is your favorite dahlia variety?

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