Q. Many of my vegetables, especially tomatoes, are lush with green growth but produce little fruit. What’s going on?
A. Quite possibly you are over-fertilizing. UC Davis has conducted numerous trials with field crops to determine the effects of over-fertilization on production, shelf life and the environment.
With leafy vegetables — celery, cauliflower and lettuce, too much nitrogen (our soils generally contain sufficient amounts of the other nutrients) eventually causes salt buildup problems. With tomatoes, the researchers say, it’s “absolutely possible” that too much nitrogen results in lower yields.
In carrots, it can cause cracking. As for the effect on shelf life, excessive nitrogen reduced that for broccoli. With carrots, applying half the nitrogen resulted in equal shelf life, and there was no evidence that additional nitrogen was useful.
On cotton, additional nitrogen increased aphid and whitefly infestations. Both too little nitrogen and too much increased disease susceptibility.
Since plants don’t take up excess nitrogen and phosphorus, these end up in our waterways, where they cause polluting rampant algal growth and “dead zones.”
To avoid these problems, plant nitrogen-fixing winter cover crops and fertilize with organic matter, like well-composted manure, which release small amounts of nitrogen over long periods.
The Shasta Master Gardener Program can be reached by phone 242-2219 or email firstname.lastname@example.org