Have you grown potatoes in the past and they turned out very small? If the answer is yes, then there will likely be a few reasons why this happened. One of the most important questions will be how much fertilizer was applied. But do you know what is the best fertilizer for growing potatoes?
The main mistake which many people make is not knowing the N,P,K breakdown of the soil. Not knowing these figures means the soil may not contain the right ratios of these nutrients to grow a crop of large potatoes.
Potatoes need fertile soil to grow successfully – if you skip this your crop will suffer in size and development.
What is even more important is getting the ratio of N, P, and K correct for growing potatoes. If you add large amounts of the wrong nutrient like nitrogen (potatoes do not need large amounts of nitrogen) then you will be doing more harm than good)- more on this later.
How to test soil for nutrients
You should carry out a soil analysis by either buying a soil test kit online or by sending a sample of your soil to an agricultural testing lab. I have found many of the kits online in which you do the analysis are hard to interpret and are a little vague. A more specific way to do soil analysis would be to get your local Agri supplies stores to arrange it.
After collecting the soil sample you put it into the bag and send it off to be analysed. An accredited lab tests it and sends you the results. The accredited lab should email you the results within a couple of weeks.
What type of fertilizer?
Choosing the type of fertilizer for growing your potatoes is a matter of personal preference. There are many different ways you can help your potatoes to grow, you can choose the organic route or standard chemical fertilizer.
Whichever way you choose to fertilize your crop (and you will need to apply some type of fertilizer to grow a good crop of potatoes) you need to decide if you are going to apply your fertilizer in a general way or if you want to add it in a specific way.
Adding farmyard manure/ compost for potatoes
For those who want to add fertilizer in a general way, I would recommend adding a wheelbarrow of farmyard manure or compost per 4m2 in autumn and digging it in well, and letting it sit until spring when you can rototill it to a fine tilth before planting.
I have an article that shows you how you can make your own fertilizer for potatoes.
More specific knowledge
For those who want to apply more specific knowledge to adding chemical fertilizer, the first thing you should do is to carry out soil analysis.
This begins by collecting a soil sample and either testing it yourself using a soil test kit bought online or by sending in your sample to your local Department of Agriculture for them to analyze.
Collecting your soil sample
To take your sample in a small area (less than a couple of m2) you simply dig down 4-6 inches and grab a handful of soil.
For larger areas, you make an imaginary x from corner to corner of your plot and take a handful every few steps along the two lines.
Mix these sub-samples together and take one sample from it. This will mean your small sample is made up of lots of small parts from all over your plot.
Reading your soil analysis report
When you receive your soil analysis results or complete your test you will have figures which relate to the amounts of Nitrogen (N) Phosphate (P) and Potash (K) that are present in your soil.
Now you have real data on how much of these nutrients are present, you should then consult the fertilizer manual I have linked to below to find out how much more of these nutrients you need to add to your soil for the crop you have chosen to grow.
These fertilizer articles are very useful reading. https://www.ers.usda.gov/topics/farm-practices-management/crop-livestock-practices/
Here is some information on a soil analysis test: https://efotg.sc.egov.usda.gov/references/public/WI/Soil_Quality_Test_Kit_Guide.pdf
This is typical of the layout of the soil analysis report you receive.
Using this report you will be able to accurately apply the correct amount of nutrients for the crop you have chosen.
What is the best fertilizer for growing potatoes?
The best fertilizer for growing potatoes is one that has relatively low Nitrogen (N) and is at least twice as high in Phosphorous (P) and Potash (K). A good example of a suitable potato fertilizer ratio would be a 5-10-10. A developing potato plant should have lower Nitrogen to prevent the top from becoming too lush and susceptible to diseases such as potato blight. The higher P and K are necessary for the potato tubers to grow large and healthy.
I have included an example of a good potato fertilizer in the link below. It is higher in P and K and lower in Nitrogen. This is essential for the proper development of your potatoes – especially for growing larger potatoes and keeping the potato tops size in check.
This potato fertilizer is: Urban Farmer Organic Potato Fertilizer with an N-P-K ratio of 3-6-6
Simply scatter the fertilizer over the tilled ground at planting time, or lay a trickle of fertilizer in the bottom of the trench you are planting into. As the season progresses you can check how they are growing to see if they need further application. Good luck!
I have made a short video of this article to act as a summary of the main points
12 thoughts on “What Is The Best Fertilizer For Growing Potatoes?”
Please help me with guidelines on the best ways to grow potatoes for greater yield and how to preserve them after harvest. Thank you for your kind consideration in anticipation.
Hello Jim for greater yield you need to know the NPK of your soil, what the potatoes require and apply the difference in fertilizer. Consult the fertilizer handbook for potatoes for figures. See my article on potato storage for some tips.
Why do the stalks be thick and hard at harvesting?
Hello John, you should let them die back for two weeks before harvesting. This make make the tops dry and brittle and easier to remove.
Thanks for this article,I believe it will guide me well as I plan to start planting potatoes
Why would I get small weird shaped potatoes? I figure it has to do with nutrients but I used a compost and potting soil in a 25 gallon container. I only got maybe a pound of potatoes off of 5 seed potatoes. It was my first year growing them and was disappointed to say the least, but not so much that I will not try again next year. Please help
Hello Maureen, I think most 25 gallon containers are around 21 inches in diameter. For that size you should plant 1 large seed potato in the middle – you probably got lots of small potatoes. Try to make sure your soil has no stones or hard lumps and your seed is good – this should prevent lumpy potatoes from forming. Let me know how it goes next time. Richard.
Very helpful site, enjoyed your video, waiting for next one.
A very helpful information. Commenting from Botswan
Would NPK. 2:3:2 work
Hello Joyce, yes it will work, apply a little and leave it for a week to see if you notice the potatoes growing much. Richard.
Thank you Joyce, Richard.