Grapefruit tree.......in zone 5

I have a potted grapefruit plant. Has anyone soaked granular fertilizer in water then water their citrus with it? What are the exact ratios of so?

From my experience with potted plants and tropicals, you really need a couple things:

  1. An actual greenhouse outside, if you want good fruit quality you need to keep them growing mostly during the months it’s likely cold there, keep in mind citrus are usually ripening December-January. Good light is needed, if you can do the same inside, that’s great, but likely your indoors is too dry and not enough light for plants.
  2. A good root system, I grew in fabric bags with a pond layer below, it was easiest for me to keep a good root system, but rootbuilder pots work well too. Generally a little bit of a rootbound system will start to fruit, whereas if you keep up-potting, your tree will keep vegetative growth.
  3. OK I thought of one more, cut back on nitrogen fertilizers, especially going into winter time. They will produce vegetative growth, which can keep flowers from forming and worse for winter means less cold resistance.

Keep in mind Grapefruit are one of the more heat loving citrus. Grapefruits grow everywhere here, and our summers are very long and very hot. Lemons on the other hand don’t require near as much consist heat.