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What is the difference between using guano, protein meals, or composts for fertilizer?

1 Answer, 1 Reply
Jennifer Martin
Jennifer Martin  replied:

This is Jennifer Martin of MarijuanaPropagation.com. 

All of these substances have different ingredients, so you'd have to send them into a lab for analysis before knowing which ones to use to supplement the minerals you seek to add. There are 13 essential minerals that plants need in the right quantities and proportions. You'll find variation from one guano type to another and from one compost type to another. Guano and protein meals in particular, are known for containing high levels of nitrogen. If you are amending coco fiber, you will need something that supplies nitrogen, but you also need sources for all of the other minerals. 

Brian Gardener
Brian Gardener  replied:

All of the materials you list are organic fertilizers, but they differ both in their nutrient content and rate of release. When using faster dissolving, high nitrogen materials one needs to be careful about over feeding. Putting in more than 0.3 lb of N per CY of potting mix with powder-like guano, hydrolyzed proteins (like blood meal), or dried manure products can result in stress or toxicity due to rapid release of ammonia. In contrast, fertilizing with dried compost-based granules can allow you to incorporate three times as much N per CY of potting mix before risking ammonia-related plant stress. Protein meals (like soybean meal and meat meals) are typically intermediate in terms of nutrient release rates but may also attract rodents or other animals, particularly if they have any fat or oil content. The most important thing to remember is that one needs to "feed to the need", i.e. provide enough but not too much fertilizer in proportion to the growing plant's needs. You can be successful with any of the materials you listed, you may just have to do many more small applications with some and fewer applications with others.