I used good composted soil to start with. Once they are started growing, and in the ground, I use Miracle Grow with a hight middle number once a week. When I am feeding by brugmansias, I do the dahlias. Then I water every morning. They are in a slightly raised bed with good drainage. I do not fertilize at all after the end of August.

Wow- so you feed them once a week? Thanks so much. I am definitely underfeeding them then!!

I use 20/20/20 once a week from early June until the end of August. I used to use Miracle Grow until I seen what 20/20/20 did for my neighbors plants.

I think 20/20/20 would do wonderfully well also.

Okay. Now to show my ignorance, what is 20/20/20? I like to stay organic; is it a chemical?
Thanks so much everyone

I use Miracle Gro and some granulars. You might be able to get a more organic product in granular. The Epsoma lines are pretty good. I did buy an Alaska soluable organic fertilizer, but it's doesn't dissolve very well in water.

I use Mighty Plant once a week. I treat my dahlias as annuals unless I really like them so I fertilize till the end of Sept. I usually have flowers till late Oct or even Nov sometimes.

please help, feeding dahlia's what does 5-10-10 mixture mean?

The numbering system for inorganic fertilizer has confused people for years. There are three numbers and they represent the amounts(as a percentage) of the three major ingredients of fertilizer: Nitrogen, Phosphorus and Potassium. "Balanced" fertilizer would have the same number for each element 20-20-20 or 10-10-10. Dahlias like a fertilizer with 5-10-10 or 10-20-20 or even 12-24-24. All this means is that it has half the nitrogen as the other two elements. Most gardens stores sell 5-10-10. Farmers buy 10-20-20 at the farm store because it is twice as concentrated and much cheaper than 5-10-10.

Most of us are going organic. Alfalfa used as mulch is a great fertilizer. Mint compost is also excellent. Both have all three of the three major elements and work quite well. Bat guano and blood meal are good fertilizers. Of course all types of aged manures are the classic fertilizers for organic gardeners. Chicken manure works great but needs to be applied in the Fall as it is too "hot" (too much nitrogen all at once) for dahlias. They say that rabbit manure can be used fresh and needs no aging.

I follow Swan Islands advice. Work lots of composted manure into the soil, put in a small handful of bone meal when planting. Thats usually it. Sometimes I'll hit them with an additional fert in September when they are in manic bloom stages, but not always. I get plenty of flowers without pumping them full of MG.