Do potato plants like acidic or alkaline soil?

  • Date: August 20, 2021
  • Time to read: 7 min.

If you are keen to grow your own vegetables at home, you are probably trying to select the best vegetables for your conditions, or at least create the best conditions you can for the vegetables that you want to grow. Many people choose potatoes as a reasonably easy and productive crop, but what kind of soil do potatoes prefer?

Potatoes will grow in soil of quite varied pH values, meaning they can cope in either acidic or alkaline soil. However, they do have a preference for acidic soil, and they are less likely to develop a disease called scab if they are grown in acidic soil. You may want to reduce the pH value of your soil to help your potatoes grow well.

What pH Value Should I Aim For?

Potatoes will grow in soils that are as low as 4.5 or as high as 8.0; they are versatile and hardy plants that will generally cope even if the conditions are far from ideal. You are unlikely to have such extremely acidic or alkaline soil in your garden, but the potatoes should keep growing even if you do.

However, to create the optimum growing conditions, you should aim to grow your potatoes in soils around 5.0 or 6.0. Neutral or low alkaline soils shouldn’t be a problem, but as the alkalinity increases, potatoes find it harder to absorb phosphorus from the surrounding soil and become deficient in this nutrient.

Very low pH soils can cause a similar problem, and will also make it harder for your plant to take up molybdenum, an essential trace nutrient that is found in the soil.

You may notice that your potato plants have yellow leaves. This is usually due to a nutrient deficiency, but if the problem is caused by the wrong pH value, no amount of fertilizer or compost will fix it.

When the pH is wildly wrong, the plant simply cannot absorb the nutrients it needs. The more the pH value climbs above 6.0 or drops below 5.0, the harder it will be for the plant to get the nutrients it needs, and the less healthy it will be overall.

Soil that is neutral or slightly alkaline will usually give you an average yield of potatoes, but nothing special. To maximize the health of your plants and the quantity of your crop, plant in acidic soil.

How Do I Measure pH Values?

The cheapest way to measure the pH value is to purchase some litmus paper. This will not give you a brilliantly accurate result but should guide you as to what kind of soil you’re dealing with, and it’s the lowest cost option.

However, you will get a lot more information from a soil testing kit, without having to spend enormously more money. These can be bought reasonably inexpensively online, and they will give you plenty of information about your soil, including what the pH is.

Understanding your soil empowers you as a gardener. It lets you know what plants are likely to thrive, and what you need to do in order to alter the conditions to help different plants thrive. It is a good idea to test your soil every year or so, as it will gradually change over time, and the test will keep you up to date on the conditions.

Soil tests can save you a lot of money in some circumstances. Misdiagnosing what is wrong with a plant can be expensive. After all, if you keep fertilizing their potatoes but their leaves remain yellow because the pH is wrong, you’ll have spent a lot of money on compost or fertilizer with no gain.

Before you try to diagnose and fix a problem, always test your soil so that you know you are addressing the right issue, and your solution will work.

A soil tester kit will come with instructions, but it usually involves scraping back the top layer of the soil in your garden and then taking a small sample from the soil beneath the surface. Add this to the tester kit and follow the instructions about how long to wait.

You should then consult the information included with the kit to help you interpret the results. There are many kinds of kits available, and some will give you more information than others. Some kits even suggest solutions for problems in the soil. It is definitely a good idea to test your soil if you’re getting keen on gardening (or even if you are already a pro!)

How Do I Alter The pH Of My Soil? 

So, if you have found that the pH of your soil is not ideal for growing potatoes, what can you do about it? It depends on whether you want to make it more acidic or more alkaline, so we’re going to cover both options.

Before we discuss the methods, it is important to point out that altering the pH of your soil does not happen overnight. It can take months to change the pH, and you may have to wait until the following year before you can plant in the space.

How To Make My Soil More Acidic

There are quite a few different ways to make your soil more acidic. Some are commercial products and some are things that you may have at home.

Firstly, you can buy sulfur as chips or as dust, and this can be sprinkled on top of the soil’s surface. Over the next few weeks or months, the sulfur will slowly make your soil more acidic. It is worth noting that sandy soils will change much more quickly than clay ones, and clay soils will need considerably more sulfur to alter their pH value.

If your soil is alkaline, you can make it more neutral by adding compost to it. This will feed the plants and reduce the alkalinity, so it can be a good option if you already have potatoes growing and you don’t want to dig the whole bed up.

Ericaceous compost is more expensive but will have a greater impact, as it is acidic, rather than neutral.

Alternatively, if you have a pine tree, consider adding a thick mulch of pine needles to the surface of the soil. These are acidic and as they break down, they will help to decrease the soil’s pH. However, they may not be as effective as ericaceous compost or sulfur.

You can also add vinegar to your soil, but this must be heavily diluted and done with great care, otherwise, you are liable to kill your plants. Vinegar is very effective for weed control and should not be added directly to any plant unless you want to kill it.

How To Make My Soil More Alkaline

You probably won’t want to make your soil more alkaline for potatoes, but in case you do, it is best done by applying lime to the surface. This can be purchased commercially and spread on top of the soil, and then dug in.

It is important to dig lime in, rather than leaving it on the surface. The more you increase the lime’s contact with the soil, the more effective it will be, as it is not very water-soluble and may otherwise have little result.

dirty potatoes
Do potato plants like acidic or alkaline soil?

What Is “Scab”?

Scab is an unpleasant disease that disfigures your potatoes and makes them look very unpleasant and unappetizing. It is frustrating to end up with scab on your potatoes when you have spent a lot of time growing them, and you may find this disease on other thin-skinned root crops such as carrots and parsnips too.

Potato scab is the result of bacteria in your garden soil, which is a very common issue. You can still eat the potatoes that have been infected by scab, but you need to peel them first to remove the rather unappealing exterior that the scab causes.

Scab is more likely to form if you grow your potatoes in alkaline soil, so it is best to reduce the pH value and make the soil slightly acidic if possible. This may not completely stop scab from infecting your potatoes, but it will decrease the risk.

You can also plant scab-resistant varieties, but these tend to have thicker skins and this limits your options, so it is best to go for acidic soil as the solution where possible.

What Else Do Potatoes Need?

You might be wondering if you need to do anything else to keep your potatoes happy. The answer is that they are heavy feeders, so they do like a lot of nutrients in their soil. Making sure they can make use of these nutrients by balancing the pH to their liking is important, but you also need to make sure the nutrients are there.

Conclusion: Acid Or Alkaline?

Acidic soil is best for potatoes overall, although highly acidic soil will cause problems by making it harder for the potatoes to absorb phosphorus. You can alter the pH of your soil using many commercial options such as ericaceous compost or sulfur, or you can use homemade (but possibly less effective) methods such as pine needles.

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