Updated: Sep 25, 2019
Dahlias are some of the most swoon worthy blooms you can find in a garden. What is more, they reach their pinnacle in the late summer when the rest of the garden is looking tired. They are also some of the easiest to grow--could you ask for anything more? Here I will detail a few of the different types of dahlias and offer a step by step guide on how to grow them. If you do, come July and August your garden is sure to be the envy of the neighborhood and your home swimming in cut flowers.
Dahlias don't just make dreamy cut flowers, they make dreamy cut flowers you usually can't buy without access to florist-only wholesalers. Then, even if you did have access to these markets, dahlias are SUPER pricy per stem! But this year YOU won't have this problem because you are just in time to grow your very own dahlias. With the slightest planning and by following these simple guidelines, you will have your very own, exclusive access to dahlias in less than 100 days!
Dahlias take anywhere from 90 to 120 days to produce flowers. The bigger the bloom, the longer they take to flower. Here in Colorado we only have 140 frost free days, which means my dinner plate dahlias (the jumbo ones the size of a head) used to start blooming just in time for the winter to kill them all off. This is why I start my dahlias in pots as soon as I can! I also often grow them completely in pots so that when it does get cold, I simply move them indoors and keep harvesting! (Of course, my greenhouse helps immensely with this but before I had a greenhouse I moved them straight into my house--luckily my husband loves dahlias even more than I do!)
So, where to buy Dahlias? There are a number of places you can buy from, I love Swam Island Dahlias and Arrow Head Dahlias (They are a Colorado Farm!) but both sell out fast and by late winter are pretty depleted. A great source for dahlias is Brecks and Eden Brother's and their dahlias usually go on sale by late February!
The first question you want to ask yourself is: what size dahlia are you interested in? The best dahlias for cutting come in three general sizes: pom pom dahlias, mid-size dahlias, and dinner plate dahlias. There are also carpet and border dahlias that look fantastic in the garden but their stems are too short to use in floral arrangements.
Pom Pom Dahlias
Pom Pom Dahlias are perfectly round gems of flowers with curled petals that exhibit an almost perfect geometry and they add a touch of structured whimsy to any arrangement. This one is called burlesque and was one of my favorite new plantings last year. As the bloom aged, it turned from bright pink to a coppery rose. I also grew a chocolaty red small dahlia that was perfect in arrangments featuring sunflowers. Remember, while billowy pastel dahlias are to die for, they bloom in late summer when the rest of the garden is trending toward the bright and brashy--think sunflowers and black eyed Susan's.
These blooms range in size from 5" to 8" across and come in the greatest variety of colors. From mono-chromatic varieties to Rembrandt-esque blooms that look like a painter splattered them, the flowers make for eye-popping additions to any flower ornaments.
Dinner Plate Dahlias
Dinner plate dahlias are so named because their blooms can be upwards of 12" across. These floral giants demand attention whether mixed with a supporting cast of blooms or stand alone. Some of the jumbo dahlias that have stolen my heart in past years include Labyrinth and Cafe Au Lait.
Once you have decided on a dozen or so dahlia tubers to start your collect (I'm not even kidding), sit back and wait for them to arrive. On the fabulous day when they are delivered pop them into any pot large enough and with drainage holes with fresh potting soil and proceed to neglect them in a room above 60 degrees. Seriously, do NOT water your dahlias, do not fertilize them. If you get anxious you can spritz the top of the soil every other day or so but dahlias are prone to rot and do best left alone until green shoots appear in the dirt.
Once your dahlia has begun to grow and the outside temperatures are above 60 F you may harden them off. Hardening off simply means allowing the plant to get used to the outdoors a few hours a day for 3 or 4 days before planting them outside.
Dahlias will do fine planted straight into the ground. You may also decide to grow them in a container like I do. Container growing has the advantage of being able to move the plant as the weather dictates and also makes it easier to lift the dahlias in the fall (see my post on splitting dahlias for more on this). I have had success growing my dahlias both in the ground and in containers. As I am growing on a much larger scale this year I am putting many of my dahlias into grow bags. Grow bags are a phenomenal way to garden more flexibly or if you have a small yard. They are simply reusable bags that you plant straight into. They work great for potatoes, vegetables, flowers, you name it (large trees might not be a great idea in grow bags but otherwise, go for it!) I love these grow bags from Amazon and you get 5! per package. For dahlias I recommend the 15 gallon option. For potatoes I use the 20 gallon bags.
I plant each of my dahlias with a tomato cage around it. This is a cheap and easy way to support your dahlias as they grow and will prevent wind breakage and loss of blooms as the plant grows larger, they also become virtually invisible as your plants fill out.
Speaking of filling out, once your plant has reached 8 inches tall you will want to "pinch" the plant. Pinching simply means cutting off half of early growth to promote branching. Forcing your dahlia to branch will insure double the blooms and a more robust plant less likely to topple over and break. So, I know its hard to lop off half of the fantastic growth your young plant has achieved but I promise, it will pay off in dividend! Simply move down half the height of the plant (approximately 4 inches) and cut the top off just above a seed of leaves. With in a few weeks two new stalks will begin to grow.
That's it! Sit back and wait for your summer of flowers to literally bloom before your eyes! Come fall revisit my follow-up post on how to overwinter and split your dahlias so that next year you'll have double the blooms!