How Hard Water Can Limit Plant Growth

Do you have white buildup on your faucets? If so, you have hard water, which can cause yellowish foliage, few blooms, and lack of vigor in your bonsai.

If you see whitish stains on sinks and leaves, the problem is hard water from dissolved salts. This isn’t table salt, sodium chloride, but rather calcium and magnesium. Both of those are essential to plant health, and yet high amounts are a liability.

Hardness is easily tested with inexpensive, digital units, which can also test for pH and alkalinity. Be sure to clean the tester nib, as they can misread if dirty.

Hardness and pH are closely related. They generally move in the same direction: as hardness rises, the pH will rise.

If you have high pH and low dissolved salts (which isn’t that common), you may be in OK shape to grow bonsai. It is high dissolved salts that create the worst problems for plants, with the worst case being high pH with high salts.

We see high hardness most often in drier climates, or when municipal sources or private wells come from aquifers surrounded by limestone. Some dissolved salts are good for plant growth, with between 30 and 60 ppm (parts per million) considered optimum. High hardness, above 120 ppm, is where the fun begins.

High hardness (and therefore, usually, alkalinity) causes several problems:

• Hard water may limit the root’s ability to draw in water—an osmotic issue
• Even moderately hard water limits the uptake of nutrients—nitrogen (causing chlorosis), and zinc, manganese and copper
• Phosphorus binds to the calcium in the soil—a macronutrient needed for many plant processes
• Stunted leaves and leaf damage may result from these nutrient lockouts
• Poor root growth is another factor

These are serious issues that add layers of stress to bonsai, which are already stressed by being in a small pot. In moderate situations of high hardness an acid injection into your hose system can work to mitigate these bad effects. This is an industry standard way of combating high pH and high hardness (and I’ll cover this shortly in another blog post).

If your electronic test kit shows much higher hardness, 400 ppm or higher, consider these solutions:

• Collect and use rainwater
• Set up a reverse osmosis (RO) system
• Do not use a water softener, which introduces sodium into your water and can weaken your bonsai

Collecting rainwater: In some areas the rain might be suspect, and in other areas it’s better than the municipal or well water for plant growth. Collection tanks may be set up, and then pumped or gravity-fed into a hose for watering. Years ago I set up a gravity-fed rainwater tank when I lived up in the mountains of Arizona, and I’ve fond memories of it as my most efficient and low-cost watering system. Since then my collection has swelled beyond the practicality of this otherwise excellent solution.

Reverse osmosis systems: While not cheap to set up, and needing electricity to run, they do work well for extremely hard water. We get high quality water out of these units which can almost magically change the health of bonsai in tough water situations.

Water coming out of a properly functioning RO system should have a pH of 7 or slightly lower, with almost no dissolved salts. Rainwater will be slightly acidic and similarly soft. Because of this nearly complete lack of minerals in both rainwater and RO systems, we do need to be consistent with fertilizing.

It’s worth investigating what’s coming out of our faucets. Good water quality is a game changer in growing bonsai. Next post will cover acid injection into your watering hose to bring down pH, which can, with moderately hard water, correct many hard water challenges.

Note: Definitely educate yourself on RO systems if you choose to use them. They will need frequent filter changing, more often if the water is very hard. Be wary of low end units as they may not give high quality water.