Most ornamental and edible plants prefer relatively neutral soil, but some gardens can be naturally acidic, or soil may become acidified due to other factors. Certain fertilizers and fresh manure, as well as environmental issues like acid rain, can cause soil pH to drop.
By definition, neutral soil has a pH of between 6.6 to 7.3. Acidic soils have a pH below this range, while alkaline soils have a pH above this range.
Depending on the crops you intend to grow, you may need to adjust your soil’s pH prior to planting. Correct pH levels can be critical to plant health, as they can influence a plant’s ability to absorb nutrients correctly. In this guide, we’ll teach you how to create alkaline soil by raising the pH through all-natural methods.
5 ways to make soil more alkaline
When your plants aren’t thriving, it may mean that it’s time to get your soil tested for nutrient availability and pH levels. If your soil test shows that you need to raise your soil’s pH, the methods below will do just that.
Compost is an amazing soil additive that can contribute so much to garden spaces. It is also one of the best ways to balance out pH issues in your soil.
Compost and aged manure have a relatively neutral pH. Adding them to your garden beds can slowly adjust soil pH over time, which is the healthiest for your plants and your garden. While this technique will take longer to raise soil pH than some other treatments, it is all-natural and will improve the overall health of your garden.
Not only can compost adjust pH levels, but it enhances your soil structure. Compost loosens up compact, clay soils, and it helps loose, sandy soils hold water and nutrients in better as well. Compost also contributes a lot of nutrients to your plants to support their health and growth.
To apply compost to your garden, add about 2” of compost over your beds and then work it into the top 6” of your soil.
While you can purchase bagged compost online or at garden centers, for a more budget-friendly solution, consider investing in a home composting bin and make your own. The more often you use your home composter, the more it will reduce your gardening costs and pay for itself.
Lime is produced from ground limestone or chalk and is a very popular soil additive used to “sweeten” or alkalize soil. Very easy to apply, lime can be readily found at most garden centers, and it is very effective for raising soil pH. That said, it’s best to apply lime as soon as you can, as it can take a year or more to raise soil pH.
If you’re growing an organic garden, you can use either calcitic lime or dolomite lime. Both limes work well; however, dolomite lime also contains a large amount of magnesium, which may or may not be needed in your garden. If your garden soil is already rich in magnesium, you’ll want to choose calcitic lime instead.
Quicklime is also available for purchase, but this lime type is not approved for organic gardens. It is also more reactive and can burn plant roots or your skin during application, and it is prone to leaching.
Garden lime can be spread across your beds by hand and then raked to distribute it. How much lime you need will depend on your garden, so be sure to follow the manufacturer's instructions when applying. In general, a 1000-square-foot garden with mildly acidic soil will need between 20 and 50 pounds of lime, but you may need more if your soil has higher acidity levels.
3. Wood Ash
People have been using wood ash in gardens for generations, and it is a wonderful way to boost soil pH and add nutrients to your beds at the same time. Using wood ash in this way also recycles ashes so that they don’t go to waste. This can be particularly beneficial if you have a wood stove or fireplace that you use frequently.
Wood ash doesn’t just alter soil pH. It also contains calcium and potassium, as well as magnesium and phosphorous in smaller quantities, making it perfect for improving your soil’s fertility. It can also contain trace amounts of iron, zinc, boron, and other nutrients that plants need.
Not all wood ash is equal, however, and you’ll want to avoid using any ash produced from treated or painted lumber. Wood ash from pellet stoves is also not recommended for garden use as it can contain polycyclic aromatic hydrocarbons (PAHs) and other toxic additives.
To apply wood ash in your garden, use dry ash and spread about 20 pounds (or one 5-gallon bucket’s worth of ashes) across your garden beds. This will produce about ¼” deep layer of ash in a 1000 square foot garden, which is enough to adjust slightly acidic soil, but you may need more if your garden is very acidic or you’re working with a larger growing space.
4. Baking Soda
For a very simple solution, standard baking soda can be used to adjust soil pH in smaller garden beds and potted gardens. Baking soda (also known as sodium bicarbonate) is very easy to find and budget-friendly, too, especially if you buy it in bulk. It also raises soil pH more quickly than lime does, but it doesn’t last as long in the soil and will need to be applied more frequently.
For standard applications, mix 1 tablespoon of baking soda into a gallon of water and then add it to a garden sprayer. Apply this mixture to your soil every few months for the best results.
5. Crushed oyster shells
Crushed oyster shells, clam shells, and eggshells all contain calcium carbonate, which can raise your soil’s pH. You can gather these items and crush them yourself, or you can purchase pre-crushed shells in bulk or from most garden supply centers.
While these materials are easy to apply and effective, they contain high levels of calcium, which may throw off the magnesium-calcium balance in your soil. To avoid this, be sure to test your soil before application to make sure oyster shells are appropriate for your garden. You can also use oyster shells in conjunction with Epsom salt, which contains magnesium, to balance out the added calcium.
Maintaining your soil’s pH levels
Once you’ve chosen the right soil amendment for you, apply it to your garden by following the manufacturer’s instructions and their recommended application rates. Afterward, water the amendment into the soil to activate it.
After a few months, test your soil again to see how the amendment is working. Depending on the results and the amendment you chose, you may need to apply more additives to your soil to further raise pH levels. Also, keep in mind that baking soda and wood ash produce more immediate results than lime and compost, but they will need to be applied more frequently.
Additionally, as soil pH levels are influenced by many factors, if you want to maintain the health of your soil, there are a few more things to keep in mind.
First, it’s a good idea to test your soil at least once every 3 years. This will help you spot nutrient and pH issues before they cause real trouble for plants.
Second, consider adding an annual application of compost or aged manure to your garden. This will maintain your soil’s health, work to neutralize pH levels, and replenish nutrients as your plants use them up.
Finally, you may also want to swap out synthetic fertilizers for organic fertilizers or compost. Synthetic fertilizers, particularly those containing ammonium sulfate, ammonium nitrate, and sulfur-coated urea, will lower soil pH levels and create an acidic environment, especially when over-applied. Natural fertilizers are usually easier on plants, and they are less likely to affect soil pH.
Frequently asked questions
Hydrangeas are well known for their color-changing flowers that can be influenced by soil pH. Acidic soils produce blue blooms, while alkaline soils produce pink or even red flowers. If you’d like to turn your hydrangea flowers pink, raise your soil’s pH levels above 7.0.
Different plants have different needs, so which plants you choose to grow may influence how acidic or alkaline your soil should be. A good rule of thumb is that most garden plants prefer relatively neutral pH levels between 6.5 and 7.0.
PH will influence the ability of plants to absorb nutrients. Improperly balanced soil pH can produce symptoms of nutrient deficiency, such as yellowing grass or leaves, stunted growth, visible leaf veining, and poor harvests.
Yes, you can test your soil pH at home with easy test kits or soil probes. However, for more accurate results, it’s best to send a soil sample to your local cooperative extension office. Not only will they be able to provide you with precise soil test results, but these offices can also recommend the best soil additives to use and the proper application rates for them.
Soil that is too alkaline may inhibit your plant’s ability to absorb nutrients properly. This can cause symptoms of nutrient deficiency to develop, such as yellow leaves, poor growth, and reduced harvest yields.
The pH of your soil may need to be altered based on the plants you choose to grow. In general, most plants prefer a neutral or slightly acidic soil pH, but this may vary depending on the plant type.
Adjusting your soil pH may sound intimidating and like something only a scientist can tackle. But raising your soil pH isn’t tricky, and it can be done with simple, all-natural soil amendments.
Which soil additive you choose to use in your own garden will depend upon your space, time commitment, and what’s readily available for you. If you have a fireplace, wood ash may make sense, or if you live near the sea, you may want to try out oyster shells. Whichever amendment you select, follow the manufacturer’s instructions to successfully adjust your soil’s pH and grow healthier plants.
Since compost is one of the best ways to adjust your soil’s pH, you may want to read up on home composting methods here.