From the Mailbag: A question about fertilizer

April 3 - Trisha writes to ask:

"I have a question about making your own fertilizer. When you mix it as you stated, what is the NPK analysis after mixing? I know it is a 'complete' fertilizer, but should the numbers be adjusted depending on which type of veggie is being planted...say spinach which needs more nitro as compared to ones that need less? OR is the the mixture one size fits all? Just curious as I want to give my plants the best chance they have..."

The fertilizer recipe is originally from Territorial Seed Company back when Steve Solomon founded it. The exact NPK rating will vary somewhat depending on the components. Digging through my old copy of Steve Solomon's "Growing Vegetables West of the Cascades", I find his statement that "the fertilizer is probably about 1:1.5:1"; but I don't buy that. Seed meal is the largest component, and while the ones I've purchased do vary somewhat, they are generally labeled somewhat higher than that - 4:2:2 or thereabouts. The bag of bone meal I just finished off was labeled 0:10:0, and the kelp I've bought usually lists some rather high potassium numbers - so I have a hard time believing the entire combination to be as low as he guesses. I do, however, think he has the relative percentages about right - my guesstimate is the fertilizer would test out to around 3:4:3 if I cared enough to get it measured. But, in the end, I just go by the amounts of fertilizer I've found works in my garden.

Regarding how I adjust to the differing needs of different plants: I just use more or less of the mixed fertilizer, without varying the component amounts... except in a couple cases where I just use one single component by itself. When I'm planting a leafy green like lettuce, for example, sometimes I'll just use cottonseed meal since those plants mainly want nitrogen. If I fertilize my peas or beans (normally I do not), I'll just use bone meal.

Over time I've learned (and continue to adjust) what works best for me in my garden. That info, grouped by plant families, is what I list in my "FAQ on Vegetable Culture".

I think it's important to point out that, if you're following my guidelines, you should consider them to be a starting point only. There may be factors that make your garden different than mine - perhaps my soil has a higher background level of fertility than yours, or vice-versa; perhaps your soil tends to be a degree or two warmer than mine, etc. So keep track of how much you give to your different plants, and see how they do - then, the next time, adjust the amount up or down if it seems necessary.