Q. Twice this year friends have come to me and said, "My tomatoes are all vines and no fruit." I asked what they were fertilizing with (thinking they were applying too much nitrogen), and to my surprise both replied: "10-10-10". I said, "That'll do it." What I don't know is why anyone would think 10-10-10 is fine for their garden—or how to help them fix the problem they've caused. Maybe by next year the crappy chemical fertilizer will be flushed out by rain and winter?
- ---Michael in Albemarle, NC
Seriously, you're absolutely correct: 10% nitrogen is only appropriate for non-flowering plants like sweet corn and lawns; it's way too much 'N' for plants that flower, like tomatoes, squash, beans, peppers, melons, eggplant, and—oh yeah, flowers! Bogus 'even number' fertilizers like 10-10-10 and 20-20-20 are always composed of concentrated chemical salts; and the super-fast growth they cause makes plants extremely attractive to pests and diseases. And those salts—originally designed to be used as high explosives—ruin the soil, and kill the soil life that keeps plants naturally healthy. And finally, despite their arithmetic rhythm, fertilizers like 10-10-10 are also unbalanced. No plant uses those three nutrients in equal amounts.
A little background: The three numbers (commonly referred to as "N-P-K") that appear on the label of every packaged fertilizer represent the three main plant nutrients: Nitrogen, Phosphorus and Potassium (which is sometimes called 'Potash'). Studies have found that the ideal ratio of those nutrients for flowering plants is 3-1-2. (That's 3% Nitrogen, 1% phosphorus & 2% potassium.) So look for that ratio on the label of packaged fertilizers; anything close to a 3-1-2, a 6-2-4 or a 9-3-6 should be ideal. (Beware higher numbers—that's the realm of chemical salts.)
My advice to folks like Michael's friends is to water on the heavy side to wash those salts out of the soil as quickly as possible, feed with compost alone for the rest of the season, and then move to organic fertilizers and/or compost in the future and sin no more!
Q. I've been growing heirloom tomatoes for a few years with reasonable success. But I would like to know how to build on that success. I understand that some fertilizers promote root growth, some promote leaves, and some encourage flowering. I have fish emulsion and a seaweed solution. Which should I use and when to maximize my tomato yield this year?
- ---Nina in Central NJ
- ---Ray from Front Royal, VA
Phosphorus—the middle number—is best known as the nutrient that produces more flowers and fruits, but it's also essential to strong root growth early in the season. Bone meal (1-11-0) is the organic source that becomes available the fastest. Many growers prefer rock phosphate or colloidal rock phosphate, which release the nutrient sloooowly, and for a long time after application—three to five years. But that slowness means you should try and apply rock phosphates the season BEFORE you want your blooms boosted, to give it time to get ready to work.
Potassium—the third number—helps plants process all nutrients more efficiently, improves the quality of fruits, and helps plants resist stress. The best single-ingredient source is green sand. Also known as glauconite, this mined mineral formed in prehistoric oceans also contains lots of important trace elements and minerals. It releases its nutrients the slowest of all—over the course of a decade; so, like the rock phosphates, always try and spread green sand in the fall in preparation for the following season.
But it's important to remember that all fertilizers—chemical and organic—rely on soil life to make their nutrients available to plants, and that high levels of organic matter in your soil are vital to the healthy growth of all plants. So all fertilization plans should begin with an inch of high-quality compost applied to the soil (preferably on top as opposed to tilled in). Then as the season progresses, you can give your plants a little boost by adding more compost or using a well-balanced organic fertilizer (remember, the ratio you want to come close to achieving is 3-1-2).
I like to use a liquid fish and seaweed mix for that boost, as these products provide a nice balance of the basic nutrients, and lots of essential trace elements from the seaweed component. Just pour some into a watering can, dilute it as directed and water it into the soil around the root zone. If you prefer granular fertilizers, spread the material evenly over the soil beginning about six inches away from the plant stem and then cover it with some soil or compost to help it get to the plants faster.