Many readers have contacted me about a recurring query- can you grow potatoes in clay soil? We all know the ideal soil to grow potatoes in is a free-draining loam, high in organic matter with a pH of 5.5 to 6.0 – but not everyone has this perfect soil for growing potatoes in.
To get to the point of this article the answer is YES – you can grow potatoes in clay soils -but, (there’s always a but) you should be aware of some key points if you want to make growing potatoes in clay soil a rewarding and pleasant experience.
Can you grow potatoes in clay soil?
Yes, you can grow potatoes in clay soils, but it may help to add amendments to the soil which will allow it to break up and not bind together. Clay soil is very sticky and can dry out very hard, this prevents water and nutrients from reaching the potato plant. By incorporating amendments into the soil we can help it break up we and overcome this problem.
How to grow potatoes in clay soil
When it comes to growing potatoes in clay soil, you should be aware that it has certain qualities which you must pay attention to. I will list the main issues which should be addressed and the reasons why in the points below:
Add amendments to loosen it up
Clay soils are well known for being very sticky and can harden like a rock when they dry – this makes them difficult to work with. Trying to grow potatoes in clay soil can be challenging – the potatoes can either become saturated in the wet soil and rot, or they can become cocooned within the drill and get no access to moisture.
To make the best attempt at growing potatoes in clay soil it is important to add amendments to the soil well in advance of cultivating for planting. The types of amendments I would advise you to add are things like homemade compost, farmyard manure, straw, leaves, coarse sand, and good loamy soil if it is available. Anything which can break up the sticky clay soil will make your growing experience better.
Check the soil pH
Clay soils are almost always higher in pH, they are naturally alkaline and can range from 8.0 to 10.0. This is a little too high for what we want when growing potatoes.
The first thing to do is to measure the pH of the soil so we know exactly what we’re dealing with. Now we can begin to lower the pH to 5.5 or 6.0 – it is unlikely that you will move the pH more than 1 or 2 points within one growing season but it is always better to try and get it down rather than do nothing.
The types of amendments you can add to lower pH are things like wood ash, coffee, vinegar, iron sulphate, and elemental sulphur. Take care to add these to the soil in increments, so you don’t add too much. I would advise you to begin this process in the previous Autumn to allow time for the products to take effect. Apply a little, incorporate and then measure. I have an article that discusses lowering the pH of soil if you’d like to take a look at it.
Check drainage is working
Because clay soils have a habit of holding onto water, it is important to check that any land drains in your plot or field are working properly. It doesn’t take very long to fix a broken drain and it makes sense to do this before you plant an expensive crop in the soil.
Observe the plot you’re going to plant into when the weather is wet and make note of where wet patches are so you can do something about it before planting time. Always choose a plot with a slight slope if you can – especially in heavy clay soils. The slope will aid the natural drainage and hopefully avoid areas of standing water. Anywhere the soil sits saturated with water no potatoes will grow.
Avoid working/ cultivating when the soil is wet
This article has advised several times to incorporate varying amounts of soil and pH amendments into the soil – but it is very important to remember that the type of cultivation you perform on the soil will have restrictions.
If your soil is wet or damp -do not work it, you will damage the soil structure and cause further issues for drainage and compaction.
Perform the following test to know if your clay soil can be worked. Grab a handful of soil and squeeze it in your hand. If it forms a ball (if it stays in shape) it is too wet to work. If the soil falls apart when you open your hand it can be worked.
Do not overwork the soil
When you have decided that the soil is dry enough to cultivate, the next step is to cultivate it. Clay soil has a fragile profile that can be damaged easily by overworking or cultivating intensively.
Clay soils are heavy and energy-sapping to work with, but you can cultivate them with a tiller or powered cultivator as long as you keep the blade speed slow and don’t break up the soil too finely. By over-cultivating the soil into a fine powder you will prevent the natural drainage from occurring and the whole plot will end up like goop when it rains. This will take a long time to dry out and you may not be able to plant anything in it for a long time.
Pay attention to watering
I wanted to add in a point about being mindful about how much you water your potatoes because clay soils are so delicate in response to under and overwatering.
If your soil is cracking on top of your drills it can be a sign that the potatoes may need water. But don’t assume so without checking – put your hand into the middle of the drill and feel the soil – if it is damp the potatoes won’t need water.
By overwatering, you run the risk of turning your potato plot into a sticky mess, and if you are approaching the wetter time of year at the end of the season, it may not fully ever dry out in time for harvest.
Harvest early in good conditions
As mentioned above, the end of the season can be wet and the later on it gets the wetter it gets. Harvesting potatoes in loam soil is forgiving — even if the soil is damp or wet, as the soil dries quickly and falls off the potatoes. Not so with potatoes in clay soils.
If clay soil is wet it is almost impossible to harvest potatoes. It cant be difficult to put one foot in front of the other never mind digging up the soil. Clay soil sticks to potatoes like glue when it is wet and it takes a long time to dry.
If you have your potatoes in your store and each one has wet clay soil on it, they tend to stick together like glue – this makes it almost impossible for air to flow through them to dry them out. Some potatoes in the wettest parts in the middle of the store usually rot.
To try to avoid these issues, aim to get your potatoes out of the ground before the wet weather arrives for the winter in your location. This can be done by pre-sprouting your potato seed in advance of planting and selecting an earlier maturing variety.
While we would all love to have amazing soil for planting potatoes in, in reality not everyone does. This doesn’t mean we can’t grow potatoes, it just means we need to know the correct way to prepare and optimize our soil before planting. The upside of growing potatoes in your clay soil is that you will have massively improved your soil for the next crop you grow! Good luck.