Re: [CH] Foliage changing color
David Stanton (jstanton@southtech.net)
Sun, 22 Feb 1998 14:38:45 -0500
I meant to respond to the original post, but I forgot. Sorry. Anyway, Chile Man makes good
points below, but I may be able to help, also. Reading back over it, it's kind of
disorganized, but I don't have time to rewrite it. I hope it helps.
First, what's turning yellow -- the top leaves, the bottom leaves, or the whole thing? If
it's the top leaves or the whole plant, then it is likely a disease problem or a problem
with nutrient transport within the plant.
If it is yellowing from the bottom leaves up, then it is almost certainly a lack of
nitrogen. Unless you are using a low-nitrogen fertilizer, the plants probably need
phosphorus and potassium as well -- it's just that the nitrogen deficiency shows up first.
If the bottom leaves are turning yellow first:
And you have been using a well-balanced fertilizer (the three numbers on the label are the
same or nearly so), use more of it.
And you have not fertilized, do so with a well-balanced fertilizer.
And you have fertilized with a low-nitrogen fertilizer, add more nitrogen, either by
replacing the low-nitrogen fertilizer with something more balanced, or by adding nitrogen
in the form of sodium nitrate, calcium nitrate or ammonium nitrate. The soda is weakest,
the ammonium nitrate strongest. Any of the three can burn the foliage if you aren't
careful.
I generally use a weak solution of a water-soluble fertilizer like Peters 20-20-20 or
Miracle-Gro 15-30-15. The Peters works well and tends to produce deep-green,
healthy-looking seedlings, but the Miracle-Gro seems to produce more roots than top
growth, which can be good if you don't want the plants to outgrow the available space
before you can transplant. The problem I have had with the Miracle-Gro is interveinal
chlorosis -- the leaves yellow in the spaces between the veins. In the absence of disease,
this is a clear sign that the plant is having difficulty transporting and using nutrients.
In the case of the Miracle-Gro, I think it is caused by the high phosphorus content, which
in turn inhibits the plant's ability to use magnesium, which it needs to produce
chlorophyll and carry on photosynthesis. I don't remember if the inability to use
magnesium affects the ability to use iron or nitrogen, but it's not vital. Calcium may
also be a link in this chain, as Chile Man notes. Anyway, the solution is simpler than the
explanation. When this happens, I just quit with the Miracle Gro and go to a more balanced
fertilizer. I also give a small dose of Epsom salts -- magnesium sulfate. This seems to
cure the problem. Be aware that when using this many different kinds of salts, it is
important not to overload the plants and burn the foliage.
Good luck,
David Stanton
Robert Farr, Chile Man wrote:
>
> Doug:
>
> Sounds like your plants may have chlorosis - an inability to
> photosynthesize. You soil could be tying up nutrients. Perhaps it's
> the wrong pH for veggies.
>
> Vegetables require a pH range of 6 - 7 (I think the perfect pH for
> veggies is 6.2). So, make sure you've planted in a good, sterlie
> potting medium (vermiculite, perlite, peat, etc. - something like
> Hyponex).
>
> In the interim, yous should use a fertilizer high in nitrogen. Soils
> which are too acidic (low pH) tie up nitrogen (and calcium and
> maganesium, among other macronutrients. A lack of calcium inhibits the
> ability of the soil to use magnesium - which can cause some forms of
> chlorosis).
>
> Harry Jiles - is that the way you see it, too?
>
> Robert.