Whether you’re getting into gardening as a hobby or to grow your own food, you may run into the subject of soil pH.
Soil pH is the measure of how acidic or alkaline your soil is. While it may sound like a trivial thing, soil pH is actually quite important as it’s one of the factors that affect plant growth. This is because soil pH directly affects nutrient availability.
The pH scale ranges from 0 to 14, with 6.5 to 7 being a neutral pH. Different plants prefer different soil pH which, therefore, requires a particular balance in soil nutrients. While some plants prefer acidic soil, it can be a problem if the soil you have is too acidic.
If your soil pH test result comes out as too acidic, you may want to make your soil a bit more alkaline.
Increase Your Soil pH
There are many ways to make your soil more alkaline. Below we’ve listed the top 8 ways to increase your soil pH. The entries aren’t arranged according to any ranking system and their use will depend on your soil’s needs.
1. Baking Soda
One of the easiest ways to make your soil more alkaline is by using baking soda. Baking soda or sodium bicarbonate is readily available in most grocery stores and is cost-effective even when bought in bulk.
To add baking soda to your soil, just mix 1 tbsp of baking soda to 1 gallon of water, stir well, then use the solution on your soil. You can repeat this process every few months.
2. Pure pH Up Concentrate
Pure Chem Co offers a product called Pure pH Up Solution Concentrate (pH Up).
pH Up is a 50% potassium hydroxide solution that improves nutrient uptake, facilitates faster plant growth, and makes plants more resistant to diseases and pests. You can use it on soil, coco coir, rockwool, clay pebbles, perlite, vermiculite, for hydroponic solutions as well as a foliar spray that helps enhance the health and growth of plants.
This product is perfect for indoor growers — whether using soil or hydroponics — because it allows them to more accurately adjust acidity/alkalinity levels in a calculated way. This is because liquid potassium hydroxide has been found to increase soil pH by increments of 1 based on a ratio of 10 kg per hectare.
To use pH Up on soil, mix 1-2 ml of the product in 1 gallon of water. You then spray this solution over your soil surface. The amount will depend on the size of your garden or the number of indoor planters you have. You can use the same formula (1-2 ml per gallon of water) for hydroponics solutions as well.
You can also band this solution with your soil when planting or replanting from a hydroponic system.
3. Wood Ashes
If your garden or farm is in a place where wood is commonly burnt in stoves, then you’re in luck. The act of using wood ashes to adjust soil pH has been around for a long time. Using wood ash is great because it’s low-cost, adds nutrients for your plants, increases soil pH, and recycles ash that would otherwise be thrown away.
Wood ash can be used if your soil lacks significant amounts of potassium and calcium or lacks small amounts of phosphorus, magnesium, and micro-nutrients like zinc and copper.
How much wood ash you’ll need will depend on the size of your garden. Generally, you’ll need just 20 pounds of wood ash (enough to fill a five-gallon bucket) for an average 1,000-square foot garden with a soil pH of 6.5.
Once you’ve spread a ¼ inch layer throughout your entire garden, mix the wood ash into the top 2 to 4 inches of soil. That should be enough for the whole year.
Do make sure your wood ash is dry before using and avoid using ash from chemically treated wood.
4. Organic Manure or Compost
Organic manure or compost is close to neutral 6.5 to 7 pH so using it in your soil brings the pH up to neutral. Compost also helps different types of soil as well. It helps sandy soil retain more water, helps plant roots spread better by loosening tightly bound clay or silt soil particles, and helps prevent soil erosion.
To use compost, apply a 1-2 inch layer on top of your soil and work it into the first 3-5 inches. You can also add several inches of compost to your garden during fall and till it into the soil come spring.
5. Garden Lime
Garden lime, also known as agricultural lime or calcium carbonate, is made from ground limestone or chalk. It’s one of the most recommended materials to increase soil pH, easy to use, and widely available in most garden centers.
Applying garden lime to your soil is as easy as raking it smooth on top of your soil, making sure to break up any large clumps. In the fall, it’s recommended to spread it evenly over dry soil by hand.
How much lime you’ll need will depend on the size and acidity of your garden soil. For an average 1,000-square foot garden, this can range from 20 to 50 pounds (9-23 kg.) of garden lime for mildly acidic soil. You may need as much as 100 pounds (46 kg.) if your soil is particularly acidic or consists of heavy clay soil.
6. Dolomite Lime
Another commonly recommended soil alkalizer is dolomite lime. Dolomite lime is nearly identical to garden lime as it too is made up mostly of calcium carbonate. The only difference being that dolomite lime has higher levels of magnesium, which may be better or worse depending on your soil’s nutrient needs.
You use it the same way and with similar amounts to garden lime.
7. Quicklime or Hydrated Lime
Did you know that while both garden lime and dolomite lime both have “lime” in their names and are usually recommended for “liming” your garden, neither of them are scientifically considered “true” lime? According to Lime.org, the word “lime”, in the context of soil and gardening, should only refer to quicklime and hydrated lime.
Quicklime is the product of the calcination (aka purification) of limestone (aka calcium carbonate and magnesium carbonate). It consists of the oxides of calcium and magnesium and is usually available in three forms in the United States. These three forms being high calcium quicklime, magnesian quicklime, and dolomitic quicklime.
Mixing quicklime with water converts the oxides to hydroxides and, thereby, producing a dry powder known as hydrated lime.
Since quicklime and hydrated lime are manufactured, it’s best to follow the instructions on the package if you want to use them to increase your soil’s pH.
8. Cement Kiln Dust
Cement kiln dust (CKD) is a product made by grinding the fine-grained, solid, highly alkaline waste product of cement kilns. This material is formed by a cement kiln’s exhaust gas going through air pollution control devices. CKD is highly alkaline due to its high lime and potassium content together with other minerals.
One study found that CKD increased soil pH more than lime despite having a neutralizing value of only 75% that of lime.
One downside to using CKD is that the nutrients it contains will depend on the cement it was manufactured from. It may require a lot more trial and error to properly balance your soil nutrients.