Q&A for How to Acidify Soil

Coffee grounds do not do a great deal to acidify the soil––scientific studies done on coffee grounds show a wide variety of results, some of which show a slight acidification of the soil but most are either inconclusive or neutral. Where coffee grounds may be helpful is as a mulch that helps plants to better access nutrients, which helps them to grow better. You might find it helpful to check out the wikiHow: How to Water Plants with Coffee .

By following the steps above, the suggestions will help you to acidify your soil properly. You’ll need to test the soil first, so you can be sure how much the soil needs to be changed, and you’ll also need to know what type of soil you have. Then, you can match the soil type to such solutions as iron sulfate, ammonia-rich fertilizer or elemental sulfur. Each method is detailed in the article above.

Although there is various "organic gardening" advice suggesting it’s okay to use vinegar to acidify soil, this is really not a good idea. The vinegar, even when diluted, can all too easily kill off the soil organisms and it can be harmful to plants and may even kill them too. As such, it’s not recommended that you add vinegar to soil but instead choose a method that is gentler on the soil biota and plants.

Although soil acidification is a natural process that occurs over a very long time (e.g., when lichens and algae break down rocks, weathering), some of the main accelerated causes of soil acidity include: Application of ammonium-based fertilizers, pollution, removal of plants by harvesting or grazing and many agricultural practices. Wikipedia has a useful explanatory article on "Soil Acidification" if you need more detail on the actual process.

Elemental sulfur is reasonably priced and is easy to distribute with a rotary spreader for a large area, or by hand on a small area.

Epsom salt is a neutral substance and will not alter the acidity or alkalinity of soil. Elemental sulfur is what is recommended.

No, pine needles are not recommended as they won't affect the acidity of your soil much, even when fresh.

They tolerate a fairly wide range of soil pH and prefer a soil that remains well-aerated. A 5.5 to 7.5 pH range would work well.

Hydrochloric acid is destructive. It will have same effects as vinegar. Use elemental sulfur or iron sulfate.

As stated above, organic material does not lower pH. Instead, it will raise it.

Depends on the plant, but most vegetable crops do best at 6.5 - 6.8.

It adds cations (ammonium, calcium, magnesium,potassium etc.). That displaces the cationic hydrogen in the soil.

You can purchase ericaceous potting compost and repot your gardenia into that. You can also purchase a special fertilizer for ericaceous plants that provides the plants with the nutrients not available in alkaline soil. Alternatively, apply sequestered iron periodically to combat iron deficiency in ericaceous plants grown in alkaline soil. Use rainwater wherever possible to water with. Especially avoid using tap water if you are on hard water.

pH sensitive papers may exhibit a range of colors depending on the solution pH. The container should have a color scale With which to compare the test strip color. Litmus paper is binary; either pink or blue and a color transition very close to neutral (pH = 7). Acids turn the litmus paper pink. Bases (alkali) turn it blue. Just remember “Base is Blue.”