Many sites advise not to fertilize in the winter. Will someone explain why? Excuse my ignorance but don't plants need their vitamins in the winter as well? It makes more sense to me use the recommended fertilizer at half straight once a month rather then not at all. Seems to me most plants are still growing in my back yard even through the winter.
It's not that you'd encourage growth by fertilizing in winter, it's that NH4 (ammonium) toxicity is a very real threat when you fertilize at soil temperatures below 55* with fertilizers deriving their N from urea and/or ammonium sources (like ammonium sulphate). NH4 toxicity is very common in container gardening and often occurs early in the season when soils are cold but growers anxious to give their plants a 'nice fertilizer boost'. Even natural sources of N (especially blood meal) can cause NH4 toxicity in plants. Excessive levels of NH4 interfere with the uptake of calcium, but more commonly, ammonium is directly toxic to plants. Some symptoms are, reduced growth, interveinal chlorosis, marginal chlorosis or necrosis of leaves, and root system damage. The conversion of ammonium to nitrate is carried out by soil microorganisms that are inactive in cold (or wet) soil. When ammoniacal N is not converted to nitrate in the soil fast enough, the plant takes up too much NH4, which damages the plant. FWIW, excess NH4 in (particularly cold) soils also further (to the cold) inhibits the germination of most seeds.
Yah! Thanks Al! Now is that going to be true for all plants. Like grass grow all year round here in Long Beach CA! Even my strawberries are on the move. And HoneybeeNC broccoli... Or should that simply be the rule of thumb.
All plants are not created equal in their reaction to ammonium uptake. Some plants are better able to convert ammonium to nitrate inside the plant. These plants probably fare better in cold soils where urea and ammonium N sources are used.
It sounds like its warm enough to grow all year, and it is growing all year as you know. I'm thinking you fell victim to articles which give one flat rule assuming everyone's garden is a medium zone 6 or something like.