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Flower Gardening

Why won't your dahlias bloom?


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February 29, 2016 3:11PM

One possible reason is over-fertilization. Here's what I do with my dahlias: 1. Fertilize early in the season (but after shoots appear above ground) and again 3-4 weeks later. 2. DON'T fertilize right before or during their blooming, but provide plenty of water and deadhead or cut blooms. 3. After blooming is completely over, fertilize again and let them build strength in their tubers for next year.

A more specific reason is too much Nitrogen fertilization. Use low-nitrogen fertilizers (like 5-10-10). Avoid the high-nitrogen water-soluble spray-on fertilizers (for Dahlias, flowering vines, and very tall-stemmed flowers like sunflowers). Also avoid using too much compost; add shredded pine bark instead to help break up hard clay soil, or as a winter mulch (but remove in spring). Lowering the Nitrogen you feed them will also help them develop stronger stems.

Also, of course, make sure you water them enough (only AFTER shoots appear). Depends on cultivar, but I've found it hard to over water dahlias and cannas.

Any plant that has 'COLOR' requires at least 6 hrs of direct sunlight per day, the more the better (usually, depending on the cultivar). The above-mentioned recommendation for a lower N2 is spot on, you also should try a 'bloom booster', or 'flowering plant' fertilizer', that would be one with a higher % 2nd number, i.e. 10-20-10. The 2nd number is the % of Phosphorus (by weight) which is essential for budding & flower blooming.