Water pH and Your Plants

The late, great Malcolm Burleigh, an award winning grower and breeder of cacti and succulents, approached me once with an idea for an article in Northern Gardener about the pH of city water and its effect on plants. Malcolm and one of his cactus-growing friends from California had discovered that city water tends to be much more alkaline than rain water and that the change in pH made a big difference in plant performance. Rain water generally has a pH of 5.6–compared to a pH of city water in St. Paul (where Malcolm lives) of 8.2 and in Northfield of 7.4. The result, according to Malcolm, is that plants don’t perform well when they are watered with city water rather than rain. A retired chemist, he recommended adjusting pH downward with the addition of acid, usually vinegar or a low-pH fertilizer. For gardeners in St. Paul, he recommends one-half tablespoon of vinegar in five gallons of water. Malcolm noted remarkable improvements in his flowers and cacti since adjusting the pH of his water.

houseplants in sun
Adding a touch of vinegar to city water may improve the looks of your houseplants.

This got me thinking about last summer. Even though I watered my vegetable and flower beds and pots regularly during the dry part of the summer (basically June and July), nothing seemed to perk them up like a good rain. Now that may well be because they got a better dousing with rain than they did with me half-heartedly hitting them with the hose, but it could also be the quality of the water. Since reading Malcolm’s article, I have been doing an unscientific test of his theory on my houseplants. I water about once a week and give the plants a good drink with tap water that has been adjusted with vinegar. (I only mix up a gallon at a time, so I need about a half teaspoon.)

Adjusting pH for houseplants is one thing–an entire garden is another. Malcolm uses a watering system that involves a sump pump, a 45-gallon garbage pail, and an octopus hose system. I don’t have the technical skills to set that up, but I may look at ways to collect rain water to use on my gardens during dry spells. I’ve seen many rain barrels around Northfield, so apparently others are considering ways to harvest rain water as well. If you’re interested in reading Malcolm’s entire article, check it out here: water.pdf

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