Most people probably don’t think of aluminum as a key nutrient for field, garden, or orchard crops, and indeed scientists don’t consider it essential for plant growth. Nevertheless, it appears to have an important role in keeping pathogens in check. In particular, we know that aluminum helps prevent late blight in potatoes, and it appears to serve a similar role in avoiding root rot in other plants.
Besides keeping plants from getting diseases, aluminum may even promote positive root growth in some species, particularly soybeans, turnips, and Douglas firs.
Aluminum is very common in soil. It can be toxic to plants, so amending aluminum levels is not advisable, even to lower soil pH for blueberries or hydrangeas. Natural ways to lower pH for these acid-loving plants would include peat moss and coffee grounds.
Because aluminum is so common, a deficiency is highly unlikely.
Aluminum toxicity can occur when aluminum sulfate is added to the soil to lower the pH. This is dangerous for both the plants and for the humans who consume them.
But even where aluminum sulfate was not used, signs of toxicity can still be found in plants grown on acidic soils (usually with a pH below 5.0), as low pH makes this mineral more readily absorbed.
Symptoms of aluminum toxicity in plants include:
- Failure to thrive.
- Increased susceptibility to drought.
- Stunted growth.
- Pale color.
- Stunted, brittle roots.
- Symptoms of calcium deficiency.
If you have determined that your plants are receiving excess aluminum, the first thing to do is to raise the pH, preferably to at least 5.5, so that your plants will stop absorbing so much. In most cases, this will be sufficient to correct the problem.
However, if you still have too much aluminum built up in the soil, perhaps from previous pH adjustments, consider growing tea or buckwheat as a cover crop for a few years. These species will help pull the excess aluminum out of the soil.