Too Much Phosphate

Symptoms of chlorosis. Image from the Washington State University

Our possible backyard lead situation is a good reason to get a soil test, but if that didn’t convince you the Garden Professors at Washington State University just blogged about another important motivation: the bad effects of too much phosphate.

An overabundance of phosphate can interfere with a plant’s ability to uptake iron resulting in interveinal chlorosis, a yellowing of the leaves between the veins. So adding fertilizer that contains phosphate to soil that doesn’t need it is a waste of money, damages the environment and can kill your plants. Of all the soils I’ve tested in Los Angeles, all are already high in phosphate, meaning that most fertilizers, both organic and chemical are both unnecessary and potentially toxic to plants.

As the Garden Professors also note in another post, it can be very difficult to diagnose problems just with visual cues. Chlorosis, for instance, can also be caused by other factors.  As Garden Professor Linda Chalker-Scott puts it, “You can’t fly by the seat of your pants on this one, folks.” While I’m probably a bigger proponent of intuition and “woo-woo” than Chalker-Scott, I think it’s a good idea to balance our left and right brains. No reason you can’t get a soil test and talk to those plant Devas.

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  1. If you’re high in phosphate you may not have that big of an issue with lead then because it makes lead unavailable to plants and animals.

  2. Do you know the exact test that was done? Only in-vitro extraction and x-ray absorption
    spectroscopy can get you those results and most soil labs do not do either of those types of tests.

  3. Hi Rachel–first test was in-vitro extraction. No Spectroscopy. I’m still trying to get down to the bottom of this. Very complicated problem! I’ll do yet another blog post about it soon and will be interested in hearing what you have to say.

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