Kelp

Kelp contains over 70 minerals and more importantly, it is an excellent source of cytokinins and auxins, both plant growth hormones. It also contains vitamins, natural chelating agents, and amino acids. It is most economically purchased in a concentrated liquid form, where a little goes a long way. 

This is one of the least expensive, yet highly beneficial products out there. It is a staple in any foliar feed and is often applied with EM mycorrhizal fungi, and other biostimulants. Definitely pick this one up if you are applying a microbial product such as EM.

The cytokinins improve soil tilth, regulate cell division and cell wall formation, increase photosynthesis and chlorophyll production, improve root and shoot growth, and delay senescence in the fall (when plants prepare for winter, dropping leaves, losing colour, etc.).

The auxins regulate cell elongation and mainly stimulate adventitious rooting, and promote fruit development.