Liquid feed is a way forward too. They respond to a good drench of anything like comfrey, nettle water etc, and also of course, the normal feeds you buy in a packet. Do it at least once a week, and don't worry about the size when planting out, just grow a few more if you have the space! I always popped them in at biro-refill stage, and let them grow into their holes as they wanted to!
I also think that as a squirt of feed collects in the top, the foliar connection holds it all there for the plant to absorb the stuff before it leaks out (pun not intended)!
Works for me!