For many years I have been making my own liquid fertiliser using Russian comfrey. It is every bit as good as expensive seaweed derived ferts, IMHO, and once you are established costs nothing. Last year I got 16.3 ounces from one lady in a 7.5 UKgallon bucket, and 50 ounces total of dried bud from 4 plants. The method is simple. You want Russian comfrey type Bocking 14, it is supplied as a root, and a google search will score you some. This is the only time you have to buy anything. Plant and water the roots as instructed by the supplier, and they will soon produce large leaves. See pic of my comfrey bed. When you have a good load of leaves, take a plastic bottle with a wide cap, I use mineral water bottles, and half fill with water. Stuff with leaves, shaking them down often, until nearly full. See next pic. The leaves just keep growing throughout the summer, in an endless supply. Leave to rot. Shake the bottle every day, and unscrew the cap to release the gases that form, they smell like a fart to be proud of. After a month you will have a dark, smelly liquid. Strain off the solids that fall to the bottom (they actually make a good compost activator) and reserve the liquid. See bottom pic. Dilute the liquid 1:20 with water as needed. I feed 2 or 3 times a week.