What is Soil pH and How Does it Affect My Garden?

10
September

In simplest terms, a soil’s pH is a measure of how acidic or alkaline it is. This can affect what crops or flowers will be willing to grow in a garden.

The pH scale typically goes from -1 to 14. Anything scoring lower than a 7 is considered acidic and anything scoring higher is considered to be basic. For reference, household lye usually registers as a 14 and battery acid usually registers as a 0. A score of 7 is generally considered to be neutral.

Most plants will tend to prefer a neutral or slightly acidic soil. For the average gardener, a range of 6 to 7 allows for the widest range of plants. There are some species that will do best in soils with a more extreme pH, though. Check the labeling on plants when purchased or consult a reputable source of botanical knowledge if unsure about a particular species or cultivar.

Untreated soil in most terrain is going to be slightly acidic. This is because the decomposition of dead plant and animal matter contributes to soil acidification. Unless a forest or grassy field is on top of a naturally alkaline geologic formation, the soil will slowly become more acidic over time. In areas with little ground cover or on limestone bedrock, however, soil pH is likely to be neutral or slightly basic.

Certain pesticides and herbicides will not work as intended in soils with extreme pH levels. More specifically, very acidic soil is unlikely to hold the chemicals, resulting in them washing away in the next big rainfall. That’s both wasteful from the perspective of the chemicals being expensive and from the perspective of the harm it can do to drinking water and the environment. Be sure that soil is not too far off of neutral before applying herbicides, fungicides, and pesticides to your garden.

Nutrient availability is directly affected by soil pH. Plants need a variety of micronutrients, but the three elements that plants need the most are nitrogen (N), potassium (K), and phosphorus (P). Most potting soils and fertilizers will have an “N-P-K” rating on them, which describes how much nitrogen, phosphorus, and potassium is in the additive. Nitrogen becomes available to plants when the pH is greater than 5.5, although there are some bacteria that can help with the absorption of atmospheric nitrogen that’s found in the air we breathe. Phosphorus, on the other hand, requires a narrow range of 6 to 7 in order to be available to plants. These two elements are extremely important to plants, and are the primary reason why a neutral-to-acidic pH can be important. No nutrients, no healthy plants. It’s as simple as that.

Soils that are too acidic can also cause toxicity to plants. Most experienced gardeners know that plants tend to have difficulty getting the heavy metals that they need. Iron deficiency is a common cause of chlorosis, for instance. Soils with a pH below 5 allow for those heavy metals such as cobalt, zinc, and iron to be absorbed more easily. This usually results, however, in the elements being overabsorbed and plant toxicity. A better solution is to mix a tiny bit of fulvic acid in a watering can and water plants in neutral or slightly acidic soil. That will allow for the roots to uptake the metallic elements without overdoing it.

If your garden’s soil is too acidic or too alkaline, there are some easy things that will alter the pH of your soil. If the soil is too acidic, then liming your garden might be a good idea. Most garden supply stores will carry lime, chalk, or slaked lime. Be sure not to overdo it, though. If the pH of your garden is too basic, then sulphur, manure, and compost are all great additives to get the pH back to normal.

Before undertaking any large-scale gardening ventures, be sure you have a good idea of what the pH of your soil is. Many state agricultural departments will test soil for free or a nominal fee. For lists of which plants prefer which pH levels, be sure to check with your local botanical gardens or garden supply store.

This post was written by

jasonjason – who has written posts on Home Tips Plus.
I'm a father of three, married and a home owner since 2006. I've worked in fixing up homes and rental properties.

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