Water Hardness and Alkalinity – Why They Each Matter

Is your faucet water appropriate for vegetation? Until one thing about each hardness and alkalinity, you may’t inform in case your faucet water ought to be used.

Is RO water, distilled water, or rainwater appropriate for vegetation? You most likely assume it’s, however additionally they have issues that relate to hardness and alkalinity.

Let’s have a better have a look at water and these two properties.

girls watering houseplants in front of a window

Key Takeaways

Hardness and alkalinity are usually not the identical factor.
Faucet water might not be appropriate for vegetation.
Pure water might also not be appropriate

Hardness and Alkalinity

Folks generally confuse the phrases harness, alkalinity, calcium and magnesium. Let’s perceive the variations.

Calcium and magnesium are two macronutrients that vegetation want.

Alkalinity is a measure of the overall carbonates (CO₃), bicarbonates (HCO₃), and hydroxyl ions (OH) and is often expressed because the equal of CaCO₃, e.g., 100 ppm CaCO₃. Though calcium generally combines with carbonates, alkalinity is just not a measure of calcium. I talk about alkalinity in additional element in What’s Alkalinity – It Might Not Be What You Suppose?

Hardness is the focus of divalent cations, primarily calcium (Ca²⁺) and magnesium (Mg²⁺), in water.

I’ve had so-called “arduous faucet” water all my life. Everybody right here makes use of an ion trade water softener to decrease the quantity of calcium and magnesium within the water.

However what is tough water? How arduous is it, and at what stage is it an issue for vegetation?

What’s Water Hardness?

Water hardness is usually expressed in milligrams per liter (mg/L) of CaCO₃ equal, or components per million (ppm) of CaCO₃ equal. 1 mg/L = 1 ppm.

Normal classifications:

Comfortable water: 0–60 ppm CaCO₃
Reasonably arduous: 61–120 ppm CaCO₃
Exhausting: 121–180 ppm CaCO₃
Very arduous: >180 ppm CaCO₃

What stage of hardness is detrimental to vegetation?

<100 ppm CaCO₃ (comfortable to reasonably arduous water): Often effective, little danger for many potted vegetation.
100–200 ppm CaCO₃ (arduous water): Nonetheless usable, however delicate vegetation (like blueberries, azaleas, some orchids) might present stress from extra Ca/Mg or diminished uptake of iron and different micronutrients.
200–300 ppm CaCO₃ (very arduous water): Typically problematic in containers — could cause leaf chlorosis (iron deficiency), salt buildup in soil, and scaling on pots. Common leaching and acidification could also be wanted.
>300 ppm CaCO₃: Thought-about detrimental to most potted vegetation except managed (acidifying brokers, reverse osmosis, or mixing with rainwater).

Ideally, the water ought to have a hardness of lower than 200 ppm CaCO₃, and 100 is even higher.

What stage of calcium and magnesium is really useful for fertilizer options?

The really useful quantities range relying on the supply of the knowledge; nonetheless, the next are the most well-liked.

Calcium: 40-120 ppm, with 100 ppm a typical suggestion.
Magnesium: 20-40 ppm, with 25 ppm a typical suggestion.
The ratio of calcium to magnesium can be essential and ought to be within the vary of 3-5 ppm calcium per 1 ppm magnesium.

Notice that there’s a decrease restrict for each calcium and magnesium. The pure sources of water are nicely beneath this stage and are due to this fact not appropriate for vegetation except you add these vitamins.

How does this evaluate with the really useful hardness values? If we convert 100 ppm Ca and 25 ppm Mg to hardness values, we get:

Calcium = 250 ppm CaCO₃ and Magnesium = 100 ppm CaCO₃, for a complete hardness of 350 ppm CaCO₃.

That’s considerably larger than the above really useful most worth of 200 ppm CaCO₃?

There appears to be one thing unsuitable with the numbers? Fertilizer suggestions counsel calcium and magnesium values that end in a hardness that’s far too excessive. To know this discrepancy, we even have to take a look at alkalinity.

What’s Water Alkalinity?

When business fertilizer options are made up, they have an inclination to make use of pure types of water, together with RO, distilled, and rainwater. These haven’t any carbonates, so the alkalinity is zero. Comfortable faucet water additionally has only a few carbonates.

Nevertheless, arduous faucet water often has larger ranges of carbonates, and the carbonates are a much bigger drawback for vegetation than hardness (Ca + Mg). Excessive alkalinity (i.e. a excessive quantity of carbonates) causes salts to precipitate out as white deposits on soil, which may hurt roots. It additionally raised the pH, which is dangerous to vegetation.

When organizations develop hardness suggestions for vegetation, they have in mind the truth that excessive hardness is usually related to excessive alkalinity. By limiting the hardness, additionally they restrict the alkalinity, in order that they advocate decrease, safer ranges for hardness.

What are the secure limits for alkalinity? These pointers are based mostly on greenhouse research.

< 60 ppm CaCO₃ – Preferrred.
60–120 ppm CaCO₃: Usually secure. Substrate pH might rise slowly; most houseplants tolerate this nicely.
120–180 ppm CaCO₃ – Borderline. Monitor substrate pH; acidifying fertilizer or occasional leaching could also be wanted.
> 180 ppm CaCO₃ – Unsuitable for potted vegetation. Tends to lift pH too excessive, inflicting micronutrient deficiencies (particularly iron, manganese, zinc).

What does all this imply?

If you’re making fertilizer options with pure water, or in case your faucet water has a really low alkalinity, you need to use larger ranges of calcium and magnesium from the fertilizer. You’ll be able to even make your individual Cal-Magazine combination from eggshells and magnesium sulfate.

Nevertheless, most faucet water tends to have larger alkalinity and hardness, and chances are you’ll want to scale back them earlier than utilizing the water. In that case, it’s best to dilute the faucet water with some pure water, which incorporates RO, distilled water, dehumidifier water, and rainwater.

How A lot Do You Dilute Your Faucet Water?

Let’s take a look at my faucet water for example. I checked with my metropolis water division, and like most water departments, they publish annual reviews that embrace water high quality knowledge. I obtained the next values from them.

Calcium – 120 ppm
Magnesium – 35 ppm
Akalinity – 290 ppm CaCO₃

Some reviews additionally provide the hardness, but when not, you may simply calculate that. To transform the primary two numbers to a harness worth, use this components:

Hardness as ppm CaCO₃ = (calcium ppm / 0.4) + (magnesium ppm / 0.25).

My hardness is 440 ppm CaCO₃.

Based mostly on the above suggestions, I ought to hold my hardness beneath 200 (100 is even higher) and my alkalinity beneath 120.

Soil Science for Gardeners book by Robert Pavlis

A combination of 1/3 faucet water + 2/3 pure water would end in an approximate hardness of 150 and an alkalinity of 100.

That provides me water that has plenty of calcium and magnesium, however not an excessive amount of carbonate. For pure water, I exploit a mix of rainwater and dehumidifier water. Each are free, which is an effective factor since I exploit lots for my tons of of streptocarpus and orchids.

To this water, I add artificial fertilizer with an NPK ratio of 3-1-2 in order that the nitrogen stage is 100 ppm. This fertilizer doesn’t comprise calcium or magnesium, since my faucet water already has sufficient.

Use my PPM Fertilizer Calculator to determine how a lot fertilizer to make use of.