What Causes Soil Acidification? What plants grow there? How to understand an acidic soil?
We will see all this in this article, but let’s already define our topic.
What is an acidic soil?
To begin with, know that knowledge of the soil is fundamental in a permaculture garden. And this involves, among other things, determining the acidity of the soil.
This acidity is measured on a scale (based on the presence of H+ ions) from 0 to 14, called PH (Hydrogen Potential):
- With a PH below 7 we are talking about an acidic soil;
- It is neutral if the pH is equal to 7;
- And if the pH is above 7, the soil is said to be basic (or calcareous).
For optimal development of most plants, a pH between 6 (low-acid soil) and 7.5 (slightly calcareous soil) is ideal. However, some plants, rightly called acidophiles, prefer soil with a PH of less than 6…
And remedying soil acidification remains possible, as we shall see later.
What Causes Soil Acidification?
Land acidification is often the result of:
- Chemical fertilizers, especially ammonia;
- By leaching of mineral elements, either by leaving the soil bare or by excessive watering;
- Organic fertilizer (but in this case a slight acidification is normal, and not problematic, as we will see later) or acidic minerals (urine, nettle fertilizer… which should not be abused)
Certain plants, when they predominate in the spontaneous state, tell us that a soil is acidic. We should mention in particular heather, Roman chamomile, chestnut, broom, rushes, pansy, sheep’s sorrel, rumex with blunt leaves.
I also present, in the article on soil knowledge, a simple test with baking soda (baking soda is calcareous, an effervescence reaction occurs with acidity).
Finally, if you want to determine the PH of your soil more precisely, you can ask for a chemical analysis (Many garden centers offer it… And you will know other data about your soil… But count on a hundred euros), or use a PH meter for the soil, or strips (unreliable)
What are the disadvantages of acidic soil for crops?
In a really acidic soil, the soil life is strongly disturbed.
You will therefore find it difficult to find earthworms there… And the micro-organisms living in the soil (fungi, bacteria, etc.) will be active a lot slower.
This can potentially lead to poor absorption of mineral elements (nitrogen, potassium, phosphorus, trace elements, etc.) by plants, leading to deficiencies and poor plant growth.
These plants, which are not vital, will also be more susceptible to disease or animal attacks…
Add to that the fact that metal ions are easily absorbed by plants in acidic soil. So if they are present in the soil, contaminant metals such as lead, cadmium or mercury can end up in your fruits and vegetables… Well, don’t panic: unless your garden is on the site of a former factory or waste disposal facility, these will metals are rarely present in significant amounts.
We will see below how to remedy excessive acidity in the soil, but you should already know that some plants, on the other hand, thrive perfectly in acidic soil…
Which plants appreciate the acidity of a soil?
Is your soil acidic?
Take the opportunity to grow acid loving plants (commonly known as “heath ground plants”):
Weakly acidic soil
It is believed that with a PH between 6 and 7 (corresponding to a low fizz with the bicarbonate test) a soil is weakly acidic.
The mineralization remains correct. And most plants normally adjust to such a PH.
These are the plants that will grow without problems (if there are no concerns other than the PH) with this low acidity:
- Fruits and vegetables: garlic, asparagus, Swiss chard, carrot, cauliflower, kale, Brussels sprouts, broccoli, cucumber, zucchini, shallot, strawberries, raspberries, currants, beans, endive, turnips, peppers, potatoes, radishes, rhubarb, tomatoes.
- Herbs: garlic, basil, chives, fennel, sorrel, parsley, rosemary, sage, thyme
- Flowers: aster, bellflowers, chrysanthemums, dahlias, delphiniums, foxgloves, gladioli, hyacinths, lavender, lupins, lathyrus, primroses, roses…
Vegetables with a pH between 6.5 and 7.5, such as artichokes, beets, celery, head cabbage, squash, spinach, beans, lettuce, onions, leeks or peas, can be a little more difficult to grow in soil with a PH between 6 and 6.5… But if you amend your soil correctly, you will have good harvests.
very acidic soil
When the pH is below 6 (strong effervescence in the bicarbonate test), the soil is considered highly acidic.
And the choice of crops is a priori more limited:
- Fruits and vegetables: asparagus, carrots, zucchini, shallots, strawberries, raspberries, gooseberries, lamb’s lettuce, blueberries, parsnips, peppers and peppers, potatoes, rhubarb
- Aromatic herbs: chives, fennel, parsley, sorrel, rosemary…
- Flowers: azaleas, camellias, bluebells, cosmos, delphiniums, irises, lilies, lupins, rhododendrons…
Fruit trees generally do not like too much acidity…
But here too, if you enrich your land in a sustainable way, you can easily expand the cultivation options.
We will now look at how to increase the pH of a soil, if necessary…
Raising the pH is not always necessary
Base soils with low PH
Some soils have a low PH (below 7) while being rich in calcium.
Simply put, this calcium is not released into the soil, often due to blockages. Making fundamental adjustments to this type of soil would therefore only disrupt microbial life a little more…
The following plants, if they dominate, probably indicate such a land: capselle shepherd’s purse, meadow sage, walleye, field maple…
In this case, don’t try to raise the PH with lime additives… Instead, enrich your soil as we’ll see below.
A humus-rich soil often has an acidic PH… This is normal.
This type of soil is rich and naturally ensures good harvests of all kinds of fruits and vegetables.
Again, lime amendments will not help.
Nature is well made!
A plant never just spontaneously appears…
And that also applies to acidophilic plants.
As they develop, they will of course tend to rebalance the PH… It is then a matter of patience (several years).
Expand cultivation options in acidic soil?
Enrich your soil with humus!
As we have just seen, a humus soil, while it may have an acidic PH, will allow most plants to grow. Even those that are normally quite adapted to calcareous soils.
Therefore, and this is in any case a recommendation that I will continue to make, your goal should be to improve the soil in your garden with the right inputs.
In acidic soils, additions of compost and manure (prefer horse manure – cow manure is more acidic) will be particularly helpful.
Similarly, ground covers with an RCW of deciduous trees (don’t use conifers in this situation), straw or even dead leaves will contribute to the gradual (yet lasting) humus formation of the soil in your yard.
Sow “pH corrector” green manures
In addition to their beneficial effect on the structure of the soil, certain green manure crops have the ability to correct the PH of a soil.
This is particularly the case for lupine, millet, sweet clover and buckwheat.
Raise the PH with lime amendments
The above solutions, cheaper, and especially without risk if the soil in your garden is alkaline, but with a low PH, are preferable in my opinion.
But the effects are slower…
Therefore, lime adjustments will also raise soil pH more quickly. Try not to go too fast though…
These are crushed limestone, dolomite, marl, chalk, lithothamne or maerl (avoid if possible… Stocks of these seaweeds are running out). Respect the frequencies, doses and methods of intake recommended by the manufacturers or distributors of these amendments… Any abuse that could harm the health (of the soil)! Generally, these contributions are made in the fall or early winter. They are buried superficially in the ground by a light claw.
On the other hand, I strongly advise against (pun intended…) lime, very harmful to soil life in the long term…
Baking soda can raise the pH of soil that is too acidic. Just bury a few small mounds of baking soda; this will reduce the potential acidity of your soil. But be careful, it is better to start with small amounts and then test the acidity again about 1 month after the addition… Otherwise you risk ending up with a soil that is too calcareous…
And if you’re lucky enough to have it, keep in mind that wood ash is also a high-quality (and free) limestone amendment.