My well water has a PH of 8. I find that over time my house plant soil gets
more and more alkaline from watering. When I fertlize, I prefer to use an
acid fertilizer to compensate for the alkaline well water. but....
The only acid fertilizer I can find is Miracid with an NPK of 30-10-10. I
prefer a more balance NPK of 20-20-20. Does anybody make a 20-20-20 acid
water soluble fertilizer? I'll settle for anything that doesn't have that
big dose of nitrogen.
I have a bunch of Citrus in pots and the Alkaline soil shows up as yellow
Most soluble fertilizers such as 30-10-10 make soils acidic because
they are rich in ammonium phosphates and urea. As their nitrogen is
converted to nitrate form, hydrogen ions are released.
A 21-7-7 formula is one of the most acidic. Its main ingredient is
ammonium sulfate, which turns soil moisture into a sulfuric acid
For citrus in containers, use a commercial citrus food, which is
acidic. Unfortunately, current formulations seem to lack zinc,
which citrus needs. Try to get some zinc sulfate, which is
sometimes available in 3 lb bags at some nurseries.
For my dwarf citrus in 18-inch tubs (see
<http://www.rossde.com/garden/dwarf_citrus.html ), I use about a
handful of commercial citrus food and a heaping teaspoon of zinc
sulfate once a month, starting in late March and ending in
September or October. Commercial citrus food is granular; zinc
sulfate is a powder. I dig them in about 1-2 inches when the
potting mix is damp. (Never feed a plant when the soil is dry!) I
immediately water the tubs to settle the potting mix and start
dissolving the fertilizer.
Between these monthly feedings, I scatter about 2 tablespoons of
ammonium sulfate on the surface of the potting mix about once every
10 days. The tubs do not sit in any container, so the nitrogen in
the citrus food quickly leaches away and must be replaced.
In general, if your water is "salting" your plants in pots and
containers, you need to leach them at least once a year. Remove
the pots from any saucers or other containers. Water each pot
once. Scatter a small amount of gypsum on the surface of the
potting mix. Water again until it flows out the bottom of the
pot. Water again the next day and the day after, each time until
water runs out the bottom. Use a wire brush to remove any mineral
crusts from the pots and from any saucers or other containers in
which they sit. (I recommend gypsum because that is what the Dutch
use to help remove salt from the land they reclaim from the sea.)
David E. Ross
Climate: California Mediterranean
I like to mulch my houseplants wen I put them out for the summer.
Both coffee grounds or wood chips as mulch will buffer the water
effectively (they both have a pH of 4 to 4.5, so a pound of coffee
will buffer some thirty pounds of water for an overall pH of 6.6).
Wood chips are low N, medium P, and medium K, coffee is medium N, low
P, and medium K. I also put a few earthworms in the pot to turn the
soil (only real way to keep soil fluffy in a pot) and fertilize a bit.
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