#1-they aren't getting enough sun to keep them from getting spindly, keep using it so they will be continually pinched back
#2-one 12" pot depending on how deep would have been best for one plant, that said since it is only August transplant the 3 plants into a much larger pot...at least 2-3 inches wider and fertilize with worm castings or kelp emulsion if you want organic. You may want to fertilize at 1/2 strength after that every other time you water.

Basil will continue to grow until the first frost. So what have you got to loose. Hope you have been using what you have.
Karen

Thanks, sounds like I need to repot and I have a good source for worm castings. I pinch back a lot and am using what I have as fast as the plants produce ... my basil has great flavor, I just wish there were a little more of it.

Can you give me more specific directions for how to apply the fertilizer to the soil?

Worm castings you can work into the top of the soil, I don't know how much. I don't think they are toxic, just sprinkle them around the plants...you don't want the castings to touch the stems...and work into the top inch of soil. Or you can make a tea, take a cup of castings into an old knee high stocking and soak overnight in a gallon of water. And water around the roots, you can use this tea for your regular watering. Hope this helps.

Thanks, very helpful. I have one last question. If I repot in, say, a 15 inch pot, can I reuse the old soil and fill the rest of the space in the pot with compost? Or would that make the soil too rich? I am out of potting soil, but I do have compost. I would rather use what I have on hand if it will work.

It's always best to use fresh potting mix, and discard the old stuff which will almost certainly be depleted of nutrients. Just add it to your compost heap/bin. While basil likes a rich soil, the amount of compost you propose to use could be an overdose.

A thought - is it getting cool where you are? If so, you might be wasting your time repotting the basil. It could well be on its last legs, ready to die quite soon, as basil does.

Daisy, if she discards the potting soil the roots would be too disturbed to have much of a chance to make it through the rest of the growing season. But yes if you have a potted perennial/in-door plant you are repotting from a previous season you should replace the potting soil.

Water the potted plants thoroughly, wait a day, fill the bottom of the new pot with enough fresh potting soil (or if you aren't going to be bringing the pot in for the winter garden soil will be fine, but compost may be too strong as Daisy mentioned) so that when you place the root ball from the old pot into the new pot the current soil level will be level with the new pot and then fill new potting soil around the root ball. The idea is to give the plants added depth and width with out disturbing the plants roots as much as possible. Water thoroughly filling in additional potting soil if necessary. I find the best time to transplant is in the evening so the newly potted plants aren't exposed to the harsh sun right away. Remember the plant will be in shock for a week or so, so don't expect to see new growth right away. I've found that my potted herbs will last longer because I can protect them longer from killing frosts better than I can those planted in my garden.

I have some Basil in a hydroponic water well or a dwc. Anyone know what color my roots should be? I'm feeding it a 3 part vegetable liquid nutrient and I forget the name but its made for vegetable gardens like my tomatoes and peppers which are in the same dwc. Anyone know how to help with the same symptoms stated above by westminstress Brooklyn, NY and knows hydroponics?

Thanks in advance for the consideration.