How to Plant Dahlia Tubers
Ok, you’ve bought your tubers, waited for the weather to warm up, and amended your soil. Now it’s time to tuck those babies into the ground. One of the first things to think about is how you are going to support your dahlias when they get big. Ideally, you want to have your support structure in place before or at the time of planting. You don’t want to run the risk of putting a garden stake through your newly planted tubers!
Support
There are multiple ways of offering support to your dahlias. What you choose will depend on location, numbers, and materials you have access to. If you only have one or two, or your dahlias are planted in various locations, a single garden stake or a tomato cage is probably going to be your best bet. Using a single garden stake, you can tie your plant to the stake as it grows. With a tomato cage, you can generally just let it grow, maybe tucking in a few stems here and there along the way.
If you have higher numbers you are planting, you may want to opt for the corral method or garden netting. The corral method uses stakes or T-posts with twine or rope tied around the outside of your plants on both sides. I have seen this done with single and double rows. With a tighter spacing, the plants will help to support each other, and the twine around the outside helps hold everything in. With this method, you will want to add multiple layers of twine as your plants get taller. Of course find what works for you, but my recommendation would be to start with a layer 12” - 18” off the ground, then adding another layer at 30”, and a third layer at 42” - 48”. This all can vary according to the height of your plants; as there are many dahlia varieties that are shorter than 3 feet and many others that can grow to 8 feet or more! So adjust these recommendations to fit your garden and your plants.
We use garden netting here at the farm. We plant our dahlias in two rows per 100’ bed. Our first year with this method, we placed 6’ T-posts on either side of the beds at 25’ intervals. We realized this wasn’t quite enough, and ended up adding in some extra support with wooden garden stakes. Part of the problem that first year was the netting: as we unrolled the netting down the beds, we failed to pull the netting tight over each 25’ section, and there was too much play in the middle allowing the dahlias to fall over more than we liked. We were able to correct this in the middle of the season with the added garden stakes, but before the next season, we added an extra T-post in the middle of each 25’ gap, making our T-posts 12.5’ apart.
The pros of using the netting include being able to put the netting in place early and letting the plants grow up through the middle; the 6” square pattern in the netting offers excellent support for the stems/blooms; the dahlias do not have to support each other, leaving us a little extra space for air flow in our Missouri humidity. The cons of the netting are cost; added difficulty in cutting blooms; the challenge of cutting back the plants after frost.
You have to decide what is important to you and which method of supporting dahlias fits your situation and personality.
Spacing
How far apart do you need to plant your tubers? If you scour the internet you will find many different opinions on this matter. The reason for this is due to several factors: climate, available space, and personal preference being a few. In Missouri, summer is very humid. We need a little extra space for the air to be able to dry the leaves of the dahlias quicker in the morning. If there’s too much moisture, powdery mildew is just waiting to stake her claim. We also have plenty of space in the field we grow in; we are not limited in size like many people. If you are trying to squeeze more plants into a smaller growing space, you may need to tighten your spacing.
We plant our dahlias in 100’ beds. Each bed has 2 rows with tubers spaced 18” apart, and the rows are offset from each other. We also try to clean the leaves off the bottom 12” of our plants to help with air flow. In a drier climate you can space dahlias a little closer, 10” - 12”. Like all gardening, things can vary so much, you really need to do some experimenting to see what works best in your specific region. As long as take care of your plants (deadhead regularly, strip the bottom leaves, provide adequate water, etc.), they will most likely survive just fine, even if you find you need to tweak a few things next year.
Depth
Now that we’ve covered support and spacing, you’re ready to plunk those tubers into the ground. How deep do they need to be? Which way should you lay them in?
First, we recommend planting your tubers 4” - 6” deep. Dig a hole wide enough that you can lay your tuber in sideways (or a furrow if you are planting a lot!). Tubers can vary so much in shape and size: some are long and thin, others are short and fat. Look for the eye (like on a potato) and try to lay your tuber horizontally with the eye(s) facing up. If you can’t tell where the eyes are, it’s ok, they’ll find their way to the surface! Once you’ve laid your tuber in the ground, cover it over with your soil, and make sure you have a label ready to stick in the ground!
Water
Now that you’ve planted your tuber(s), resist the urge to water it! They have everything they need stored away to get themselves growing. If you add additional water, you are more likely to end up with a rotted tuber. Wait until you have sprouts that are about 8” tall—unless your soil is excessively dry. You need to let your dahlias create a root system that can start taking up the water from the ground before you start giving them additional water. As your plants get bigger, they will need to be given a deep drink at least once a week, possibly more depending on how hot and dry your weather is.
Happy growing!
These are basic things you can do to get your dahlias off to a great start. The hardest part is waiting for the day you see the sprouts peeking through the soil after planting. Sometimes this can take over a month, so try to have patience!
