what are a few excellent brand name fertilizers for Dahlias? What natural fertilizer compost is best for dahlias knowing it should be low in nitrogen and I think potassium from what i have read?
Potassium and phosphorus support roots and flowers. Most soils have enough phosphorus naturally but if you haven't had yours tested, I'd go with a fertilizer with some nitrogen and phosphorus but more potassium. Potassium is the last number in NPK listing. From the plant's point of view, NPK is NPK whether it comes from a factory as granules or organic compost. Look for 5-10-10 or similar. Compost improves soil structure and provides some micronutrients. More on dahlia fertilizer here: https://www.gardeningknowhow.com/ornamental/bulbs/dahlia/how-to-fertilize-dahlias.htm