I started growing dahlias more than ten years ago. Back then, I’d pick up a few tubers from the local garden center each spring and, I hate to admit it, I treated them like annuals. Once I learned you could dig them up, store them, and replant them year after year, it completely changed the way I gardened.
I’m planting more than thirty different dahlia varieties this year, because honestly, I just couldn’t resist the urge to add one more, than another, then another. But it will be worth it. There’s nothing better than watching the yard slowly come alive with those first blooms of summer.
I’m paying more attention to fertilizing this year than I have in the past. I’m hoping for taller plants, stronger stems, and bigger blooms, though if you ask five seasoned dahlia growers how to fertilize, you’ll probably get five completely different answers. Everyone seems to have their own tried-and-true method.
The best place to start is actually with a soil test. Your local extension office can usually help with this, and some garden centers offer basic testing as well. A soil test will tell you exactly what your plants need before you start adding fertilizers or amendments.
But to be honest, I’m skipping that step this year. Most of my dahlias are grown in containers, with just a few planted in raised beds. Here’s the simple fertilizing plan I’m following this year:
1. Refreshing Old Potting Soil
For some containers, I’m reusing potting soil from last year (all gall-free). I’ll refresh it with fresh compost and worm castings and a bit of vermiculite to add nutrients and improve soil structure before planting.
2. Starting with Fresh Potting Mix
For other pots, I’m using fresh potting mix. One thing I’ve learned: potting mix and garden soil are not interchangeable. Garden soil is too dense for containers, while potting mix is designed to drain properly and keep roots healthy in pots.
This year I splurged a little on Coast of Maine Bar Harbor Blend for waking up my tubers, and I’ll mix that with Sta-Green Potting Mix with fertilizer when I move plants into their larger summer containers.
3. Feeding for Bloom Production
Because nutrients wash out of containers quickly, I plan to start feeding once I see the first buds forming in early to mid-summer. I’ll be using Sunniland Bloom Special 2-10-10 fertilizer, which is lower in nitrogen and higher in phosphorus and potassium to support blooming instead of too much leafy growth.
Hopefully, this translates into those big, vibrant flowers we all love so much.
4. Stopping Fertilizer Before Fall
By late August or early September, I’ll stop fertilizing altogether and let the plants begin slowing down naturally as the season winds down and tubers prepare for dormancy.
At the end of the day, gardening is always a little bit of experimenting. What works beautifully in one garden may not work exactly the same in another. But that’s part of the fun, learning as you grow, season after season.
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