Growing Dahlias
Tips and Tricks for growing dahlias from tubers
Tubers: What to expect
Dahlia tubers come in all shapes and sizes. Bigger isn’t better! As long as they have a bulb, a neck and an eye, they will grow flowers.
When you receive it, the bulb part should be firm, not dried up. I have found that it’s ok if it’s a little bit squishy, but when it is in that state, it means the conditions for storage aren’t quite right. If it’s the right time of year, plant it to resolve the issue!
When they arrive, the most important thing is to keep them out of freezing temperatures. That is the easiest way to make the tuber useless! When it thaws, it’ll turn to mush. Also keep it out of higher temps—long term storage in temps above 60 degrees will tell the bulb to start growing too early OR will cause too much moisture to accumulate and it will rot.
It may have a stem growing on it already. That’s fine! Try not to snap it off, but if you do on accident, it isn’t the end of the world. Plant it anyway and it’ll grow just fine.
Planting
It is tempting to plant dahlias as soon as possible to get flowers soon. Resist this temptation. Dahlias do not appreciate cold soil, and in the rainy spring conditions of the Pacific Northwest are prone to rotting in the ground before they get the chance to sprout if planted too early. I typically shoot for May 1-15 to plant (a little earlier if I’m feeling risky or the forecast looks good!), and have planted as late ast June 10.
Dahlias grow best in well-draining soil with a lot of sun (6-8 hours per day). To plant, dig a hole 4”-6” deep that is big enough for the tuber you have. Place the tuber in the hole horizontally. If it has a stem growing already, try to place it upward but in the end it doesn’t really matter. Cover the tuber with soil. Space tubers out 12”-18” apart if you are planting multiple. If you plan to overwinter them (see below), plant farther apart to allow for tuber growth over multiple years.
At this point, DO NOT WATER IT! In our wet spring, the soil will be wet enough for what is needed for it to sprout. If you water it right away, you will run the risk of the tuber rotting. Only start watering it once the leaves poke through the ground, and even then only when the soil is getting really dry. Once they sprout, give them just enough water to keep the soil moist. Once the summer weather turns, make sure they get enough water through the dry season! I’ve made the mistake of underwatering before and it makes a difference. I water deeply 2x per week during the dry Oregon summers.
Mark the spot where it is planted, and label it with the plant marker of your choice! When you plant it, you will think you’ll remember where it is and what variety it is. You won’t. Trust me on this.
Getting Beautiful Blooms
Once the sprout appears, allow it to grow until it has three sets of leaves. At that point, the best thing to do if you want a lot of blooms is to pinch the main stem. This is going to be difficult. You’re going to question yourself when it’s time for this. You will hesitate. You still should do it. Pinching the stem will convince the plant to focus on growing two main stems instead of one—twice as many flowers!
As it continues to grow, make sure you keep cutting flowers and/or deadheading. If you do that, it will continue to produce new blooms until frost (I’ve had dahlias in November a few times!). If you don’t cut deep, it won’t be so prolific and the whole plant will become top-heavy and start to fall over. It will still bloom, but not as much and the stems won’t be as strong if you want them to be available for cutting.
Dahlias love a little support (who doesn’t!?). Support your dahlia plants with tomato cages, netting, twine, or any other support of your choice. I make this mistake every year and think I can get away without supporting them, then end up with sprawling plants that produce winding stems that are useless in bouquets.
Cutting for Bouquets
If you want the plant to primarily be used for cut flowers, cut deep on the stem. This will mean that you need to cut off some buds that are coming up on the side stems. It is a sacrifice you need to make to get great blooms for bouquets. “Cutting deep” means to cut a few nodes below the flower you want. I’ll post some videos on Instagram this summer as a tutorial on this– keep an eye there to learn more! If you don’t do this, it won’t hurt the plant, but your stems won’t be as strong.
Finally, cut them when they are just open and looking beautiful but the center hasn’t produced pollen yet. They don’t open very much after cut, and will fade quickly if you cut them too late. They will typically last 4-7 days in a vase if cut at the right time.
End of the Season
In our climate, you have two options for what to do at the end of the season. The reality is that dahlias are more finicky in the off-season than they are during their prime time in the late summer and early fall. It’s worth the effort to enjoy a few months of these beauties though!
Your options:
Let them overwinter in the ground. This should work as long as we don’t end up with a long period of freezing temps (see above note for if they freeze!). We had a terrible week of freezing temps in January this year, and the few tubers I left in the ground without any extra insulation are surprisingly still happy in the soil. If you choose this route, I recommend cutting the stems at ground level in the fall then covering the place where it is planted with an extra layer of insulation such as compost or leaves. Pros for this method: they may come up earlier the next year, and it is less work in the fall. Con: You are surrendering to Mother Nature with this method; if she decides to give us an extra harsh winter, you could lose your plants altogether. Note: I don’t recommend letting them overwinter in the same place for more than 3 years—the tuber clump will become way too big to be reasonable for digging after that, and plant quality will decrease over time.
Dig them up. This method also has its risks. Once you dig them, you want to divide and store them. You’ll need the right temperature of space to store them as well as some instructions for how to divide. I’ll write a blog post about my storage method later this summer for you. Pro: you will get more plants the next year! When you divide the tubers, each one will become a new plant. Cons: Storage can be finicky. I have lost tubers because they were too moist when they went into storage and rotted over the winter. I have also lost tubers because they didn’t have enough moisture and dried up over the winter. Tuber storage is a real Goldilocks situation!
Have questions? Leave a comment and learn along with me!
Dahlia tubers of all shapes and sizes
Dahlia flowers of all shapes and sizes
