Find everything you need to know about growing these beautiful flowers.
We've gathered up helpful information on all the aspects of growing these beautiful flowers below. We've pulled material from other growers, our own experience, plus tons resources from all over the web and tried to condense it down to cover all the topics as best we can.
Plant your dahlias after the danger of frost has past and the soil has begun to warm. Plant in well draining soil in a location that receives full sun, or a little afternoon shade.
Healthy soils grow healthy plants! We typically amend with compost and a balanced organic fertilizer, and lightly mix into our soil before planting. To truly know what amendments your soil requires, we recommend getting a soil test done.
Space your dahlias about 12 - 18” apart depending on the size of the bloom. The larger dinner plate types need more space.
Dig a hole (or if you are planting many, you can also dig a trench) approximately 4-6 inches deep and place your tuber horizontally in the hole or trench, with the eye facing up, and bury with soil.
Because tubers can rot in overly moist soil, many growers recommend not watering until you see green shoots just starting to show above the ground. Here in the Kootenays it is often quite hot and dry and our soil is very well draining, so we typically give a light watering after we plant. If your soil is moist or you’re in a rainy climate you do not need to water until the plant sprouts and begins growing roots.
Be sure to label your plants as you put them in the ground. A wooden stake works fine. Sometimes we also label the tuber itself with indelible marker before planting- the marker is surprisingly durable and is still visible at the end of the season after we dig and wash the tubers. It's really handy if you loose your labels!
Once the plant is sprouted and growing, dahlias need regular, consistent watering. We use multiple lines of drip tape to be sure that they receive sufficient water and usually water 2-3 times per week. Check the soil moisture not just at surface, but at 6 inches down to see if your irrigation is penetrating and providing sufficient moisture.
Keeping your plants well fertilized is an important task throughout the season. As we said earlier, healthy soil grows healthy plants! Often people want a specific fertilizer recipe and regime to follow, but every garden and climate is different and you'll need to tailor your program to your particular space. (Keep in mind that over fertilizing isn't good either! It can be detrimental to our environment as well as your plants.) One important thing to know is that once your plants are established, you don't want to give them too much nitrogen fertilizer. This can cause plants to rapidly put on lots of green lanky growth and result in small blooms or low flower production. According to Swan Island Dahlias, it can also be a cause of tubers shrivelling in storage.
To control weeds, you can mulch your plants. Quality straw, that is free of weed or grain seeds, works as well as decomposed leaf mulch. Often it is advised to wait to apply mulch until your plants have emerged and the weather has warmed up so that you don't unintentionally cool the soil and slow growth. You can also top-dress your plants with a thick layer of well aged, quality compost to help prevent weeds.
To encourage branching and a bushier plant, pinch your dahlias when they are approximately 8-12 inches tall. Simply snip (or pinch!) the central growing stem just above a set of leaves, leaving about 3 sets of leaves on the plant. Although it sometimes feels like it's the wrong thing to do (why am I chopping of 4 good inches of my plant?!), you'll be glad you did! It encourages the plant to branch out and essentially make more flowers with better, longer stems for cutting. Even if you don't plan to cut your flowers for the vase, it still encourages the plant to put out more blooms.
Dahlias will also benefit from staking. There is nothing worse than watching your beautiful plant that was just about to flower topple over in a rain or wind storm! Home gardeners can just use a wood or bamboo stake pounded in the ground next to the plants and then tie the main stalk to the stake as they grow. We pound in posts at the ends, and spaced about 7 ft apart along each side of, our beds. We then tie and run sturdy twine down the sides, wrapping in around each post to create a corralling effect.
Depending on your climate and the variety of dahlia, some early flowering types can start to start flowering in about 75-80 days. Remember that every variety is different and some take much longer to flower than others. Generally, smaller flowering types will be quicker to bloom.
After a couple months of work nurturing along your plants, you finally start to see the signs of flowers forming- yay!! It then takes about 3-4 weeks from the first sign of the tiniest bud to when you can pick your first flower.
Since dahlia flowers don't continue to open much after they're picked, you'll want to cut them when they're fully open (but not too open!). If you pick them too mature, the petals will drop in just a day or two. Look for flowers that are fully open and then check the backside of the bloom. If you notice that the petals are beginning to dry out or turn brown, then you have waited to long. You want the petals to be pretty and firm. It's best to pick a little too soon then too late.
When you're ready cut, use clean, sharp snips and cut low on the plant. This will encourage the plant to make more nice long stems for cutting. You'll likely have to remove a small side branch or two to get a nice long stem for your bouquet. Don't worry that you may feel like you're removing some potential flowers (you are), because the plant just keeps making more stems. Remove ay lower leaves and place in water immediately. Many growers recommend placing your stems directly into very hot (not boiling) water to get the best vase life.
Flowers will typically last 5-7 days in the vase. Keeping them out of direct sun and in as cool an area as possible will help you get the longest life out of your blooms!
Learning the right time to dig your dahlias can help you successfully shepherd your tubers through winter. According to experts at the American Dahlia Society, the most important factor in getting quality tubers that will store well for winter is make sure the tubers have at least 120 days in the ground (it counts if you start them in pots as well). Typically, you'll wait for a hard frost before you start digging. However, this isn't a requirement- it's just a good rule of thumb. There are some locations that rarely get a hard frost, or years when you may have a very mild fall and won't get a hard frost until the ground is covered in snow. Just be sure to leave yourself plenty of time to dig all your plants and safely get them into storage before the weather makes it too difficult.
Before your plants die back, be sure you have everything labeled! A good method is to write the name with permanent marker on flagging tape and tie it to the bottom of the stem just above the ground.
Whether it's frost or the calendar guiding you, you'll want to cut back your plants almost all the way to the ground. Use good loppers and cut the whole plant down, leaving just a few inches of thick stalk above the ground. We use a garden fork to loosen the soil all around the plant and then carefully lift the tubers from the ground. Go slowly and use caution. Then, gently shake or comb away the loose dirt from the clump, being careful not to break the tubers from the neck.
Now you have some decisions to make. To wash, or not to wash? Leave them whole or divide them? Should you divide them now or in the spring? Gah! So many decisions!
If you don't have lots of plants and have enough space, you can simply store your dahlias in whole clumps. Some people, who don't have heavy soils can simply brush off the loose dirt, cut the stem back to where it's no longer hollow, and store them just like that in crates, bags or boxes. Easy, peasy. You just need to make sure you have the right storage conditions- more on that later. You can then divide them in the spring or over the winter when you have the time.
Many of us don't have sufficient storage space to keep all our dahlias whole and need to break them down into smaller chunks for winter. In this case, we recommend washing them first. Washing is simple, just spray them with your hose. If you're too aggressive you can damage the skin and even break tubers from the neck of the stem (which you'll learn later isn't a good thing). Wash them as best as you can, especially in the middle of the clump where you'll want to be able to see where they all attach to the stem.
After washing, we start dividing right away and then set them out to dry someplace inside where they'll be protected from frost and the elements. We dry ours on screens in our greenhouse. Then, usually after a day or so they're ready to be packed for storage. If you notice that your tubers are starting to shrivel- it's time to get them packed!
Where and how to store your dahlias, it's yet another decision to be made! Where can you store your dahlias and what container and medium do you store them in? First learn the basic criteria and then you can find a spot and method that works best for you. Keep in mind that there are as many ways to store dahlia tubers as there are dahlia growers!
Work with your specific climate and what space and tools you have available. Here are some general guidelines:
They can't freeze! Ideal storage temperature is around 5 degrees C (40 F), or a range of 5-10 C (40-50F)
You don't want them to rot or to dry out. Typically you want high relative humidity, around 70% or higher
Good storage media are wood shavings (pet/ horse bedding), vermiculite, or peat moss. If using peat moss, just be sure your tubers are dry and the peat isn't too moist. Peat can hold a lot of moisture and depending on conditions contribute to rot. But lots of folks pack their tubers in peat, so it really just depends on your specific site!
You can use any kind of container: crates, bins, boxes or bags. We use plastic storage totes with holes drilled in them because in our climate we are usually more concerned with tubers drying out.
If you have perfect storage conditions, some people just store whole clumps loose in crates lined with paper.
Generally a basement is a great place to store your tubers. Your specific climate will determine how you will want to store them. Here our air is cold and dry and if storing in our basement we have to watch for the tubers drying out. This year we are storing them in our air-tight, insulated walk-in cooler and the humidity is relatively high, so we are watching for signs of mould or rot.
We store our tubers in plastic totes with large holes drilled in the sides towards the top of the bin. We use wood shavings as our storage medium, although we have also had great success with vermiculite (available at most garden centers) as well.
We start by adding a few inches of shavings in the bottom and then laying tubers out across the bed of shavings so they are not touching. We then add another layer of shavings to cover and keep repeating the process until the tote is full. We put only one variety in each tote and label it carefully on the inside and out. You can use the same method with any type of medium you choose- just keep layering them in and covering them up. One thing to keep in mind is that if you have many deep layers, it is more difficult to check the ones at the very bottom!
For more information on storage, please check out our blog post here.
Dividing dahlias can cause a lot of anxiety when you're first learning- and even after you've done thousands, it can still be a daunting task. But, like anything it just takes practice and you'll grow more comfortable with time. Learning a few tips and knowing what to look for when dividing will help you approach the task with more confidence.
Every plant will produce multiple tubers connected to a main central stem. You can easily multiply your stock each year by dividing off each healthy tuber that has a viable eye on it. If properly cared for, each tuber will produce a whole new plant the next season with many new tubers. You don't have to divide each one off separately, but if you want to really increase your stock this is one way to do it!
When starting to divide your dahlias sometimes just figuring out where to begin is the hardest part. It can feel intimidating. My best advice here is to just dig in- don't be afraid!
If you're ready to jump in, please visit our blog post all about dividing dahlias.