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 leaves.
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.
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 ), 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.)
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 solution.
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