How to Make Dahlias Last Longer

How to Make Dahlias Last Longer

By: Brent, Co-Owner, Brent & Becky's Bulbs

It’s hard not to love dahlias. They’re incredibly beautiful and unique, not to mention they come in every color of the rainbow - even blue! They’re just one of those flowers that we simply can’t get enough of, and we love including them in our garden bed ideas, so we certainly want to prolong their presence in our lives as long as possible. Here’s how:

Grow in the Right Conditions

If dahlias frequently go more than a week without moisture, they tend to dry out and certainly will stop blooming. To prevent that from happening, we like to encourage drip irrigation. Overhead watering is not great for them because it tends to encourage fungal growth, particularly if they’re wet at night, which is when most irrigation systems like to turn themselves on. We’ve found that most flowers - not just dahlias - perform far better if we use drip irrigation for a couple of hours once a week, bringing moisture to the soil and the roots where it’s needed and not to their susceptible but beautiful foliage and blooms.

As far as the media for growing them in, I really, firmly believe that feeding the soil with compost is the best thing that you can do, and it certainly feeds the dahlias.

Introducing Trace Minerals

Another good idea to improve the longevity and color performance of your dahlias is to introduce more trace minerals to your soil. We often garden so long in some places that most of the trace minerals have been taken up by the plants. So, it’s not uncommon to be dealing with soils that are somewhat deficient in trace minerals, like magnesium sulfate, which really brings out the colors of a bloom.

My father used to put Epsom salts on his gardens to intensify the colors, but we’ve recently discovered an even richer source of organic minerals from an ancient volcano in Utah that erupted millions of years ago into an inland sea. All the minerals settled at the lowest point and are now being mined and made into a product called A-Z Minerals, which has something like 97 minerals in it and can be added to the soil to work essentially as a multivitamin for plants. You can also use fish emulsion with kelp!

Deadhead Spent Blooms

The most important way to keep dahlias blooming for longer, though, is to remove spent flowers. Dahlias are cut and come again flowers, particularly the single cultivars, which are fantastic pollinator plants. While we love the monarchs fluttering around them during the fall migration, if the flowers do get pollinated, they will signal, “Well, we’ve done our job, all we need to do is make seeds now.” But if you take the old, fading flowers off, you’ll prompt them to bloom instead of setting seed.

Winter Dahlia Care

If you’re in Virginia or zone 7b and southward, and you garden in nice, sandy loam soil with good drainage in the wintertime, dahlias are relatively reliably hardy perennial plants. If your garden is like Becky’s, though, with heavy, gray-modeled clay in the soil that stays wet all winter, dahlias will rot. We’ve discovered, though, that by simply planting them in raised beds with about a foot in elevation, even those with less than ideal soil will have their dahlias surviving the winter, too. The key here is good drainage. Almost all bulbs and tubers like to sleep in a dry bed, so when they’re dormant, they’ll want to stay dry.

If you’re north of Virginia or zone 7b, you’ll probably want to dig them up after the first frost. Gently pull them up from the soil and dry them nicely in the shade for about a week or so. Never wash them. You never want to wash dahlias even though you’ll read online that that’s what you need to do. Washing them will bruise them and introduce fungi that can begin the process of their rotting and decomposing, and we find that people who wash them, tend to lose them. If you’ve grown them in good soil with lots of organic matter and microorganisms, they’ll be protected just fine on their own.

Once they’ve dried out, store them indoors over the winter between 40-60 degrees. Tubers like to breathe, so they give off gases that need to be able to dissipate. To encourage that, make sure to give them an area where they don’t get direct air blowing on them, but that they have access to fresh air. We find that packing them in wood shavings, rice hulls, peat moss, and any nice, airy media that protects them from bruising works well. Remember to check them periodically, and remove any tubers that are beginning to show signs of deterioration, as one rotten apple can spoil the rest.

In the spring, when you’re thinking about planting them again, we often recommend starting them inside in pots of good, coarse media with plenty of structure for the root hairs to hang onto. Give them some bottom heat from something like a seedling heat mat and get them going. By the time we’re no longer expecting night frosts or hard freezes, we can start putting them out into the garden as started plants! Really, the best temperature is above 60 degrees, but I think 50 is suitable also.

No matter which steps you take to ensuring your dahlias last, it’s important to remember that some dahlias are just better performers than others. However, with the right growing conditions and care, you can be sure to have a plant that outperforms the rest any day of the week!