How to Fertilize Potatoes : The Secret for a Bumper Potato Harvest!

One of the best tricks for growing a healthy, abundant potato crop is knowing exactly when and how to fertilize them – and just as crucially, when to stop!

Why are potatoes the world’s favorite root vegetable? Baked, fried, boiled… They are delicious, children love them, and adults too, and they are a great source of carbohydrates, a great alternative to wheat and rice for homesteaders… And these earthy tubers give you insane bumper crops if you fertilize them well. Yes, because they are easier to grow, adaptable to many climates, and they can feed us with little money invested. In fact, these natives of the New Continent are very generous indeed!

Before they can feed us, we need to feed them. Potatoes demand a lot of nutrients to grow those big, healthy tubers. Proper fertilization is essential, not just in quantity but in timing and method.

If you don’t fertilize enough, your plants will be weak, and the potato yield will be poor. I’ve seen many folks either forget to fertilize or do it incorrectly, which ruins their harvest. This is even more important if you’re growing potatoes in pots or raised beds since the soil in these can lose nutrients quickly.

The tricky part with potatoes is that you can’t see how they’re doing underground until you dig them up. It’s hard to know if they’re getting enough nutrients. But with regular and proper feeding, you’ll have strong, productive plants and a great potato harvest. Trust me, it’s easier than it sounds!

Fertilize Potatoes Before Planting 

First Things First: “Serve Food to Your Potatoes”, i.e. the Soil!

How to Fertilize Potatoes: The Secret for a Bumper Potato Harvest! 1

In organic farming, we don’t feed the plants, we feed the land! And potatoes need the right type of soil to give their best. So, first of all, make sure it is loose; if it’s hard, they will find it difficult to grow their heavy tubers. Add sand and organic matter if it is compact, or gypsum if it is clay based.

Potatoes like slightly acidic soil pH, 6.5 is ideal, but they will tolerate it as low as 5.0. In case yours is alkaline, amend it, with sulfur.

The ideal soil type for potatoes is loam, but they will tolerate clay-based earth if it is loose, well aerated and nutrient rich, and sand, as long as it is organically rich. So, amend as necessary.

Prepare a “Healthy Bed” for Your Potato Slips

Comfrey as Potato Fertilizer

As you plant your potato slips, whether you use trenches or holes, make sure they have a healthy bed, with lots of minerals… So, sprinkle a dusting of organic, natural ash in them. This will provide lots of trace nutrients, helping their immune system, and it will also prevent molds and infections! When you’re planting potatoes in trenches, put 3 to 5 Comfrey leaves at the bottom before placing the seed potatoes on top. As the leaves break down, they’ll provide natural nutrients that help the tubers grow strong and healthy.

As I said, we need to treat them like babies at this stage.

Now that we have “laid the table” and “done the bed” for our potatoes, we can talk about food!

Start Early and Pre-Fertilize Your Potato Beds

Start Early and Pre-Fertilize Your Potato Beds

Give your potatoes a great start in life, and they will reward you with fast and strong growth, and with a huge harvest later on! So, before you plant them, add 2 inches of compost (5.0 cm), which is balanced and it is also rich in trace and micronutrients.

I would suggest you do it a week or two before you actually plant your potatoes if the weather is dry, so it has time to seep into the soil. But if it’s wet, as it often is in spring, just add it when you put the potato slips into the ground.

And this is their first meal, but you will have to keep feeding your potatoes up until the end, when you harvest them.

Like Children, Potatoes Need Calcium

Here I have a little tip for you to get a massive potato harvest… When you plant your potato slips, give them some calcium. They need it to build cell walls and strong roots, and it also helps them against diseases.

But potatoes don’t drink milk, unlike children, so, give them a handful or spoonful of bone meal for each plant instead. That will be enough to keep them going for 4 months! Actually, it will start becoming available to them after a month, so you have a 3-month window of healthy growth. And that will lead you straight into harvest time!

Fertilizing Potatoes During The Season

After their “baby food”, you will still need to fertilize potatoes. But how? How often? It depends on what you use, a fast or slow-release fertilizer. But one thing is essential to get really massive tubers: potassium!

This nutrient is essential for root growth, and potatoes are, indeed, roots! So, let’s see…

How to Fertilize Potatoes: The Secret for a Bumper Potato Harvest! 2

Fertilize Potatoes with an Off-The Shelf Fast-Release Fertilizer

When the plants reach about six inches tall, it’s the right time to start hilling them up. At this growth stage, it’s also beneficial to begin a regular fertilizing routine, as potatoes require ample moisture and nutrients to help their tubers grow. If you want to use a fast-release fertilizer you buy off-the-shelf, it will save you time; it’s an easy, practical option. Choose an organic brand with NPK 5-10-10. You don’t need much nitrogen, because it will promote leaf growth.

Start about 2 to 4 weeks after planting, and repeat every 4 weeks with the full recommended dose, or every 2 weeks with half dosage.

Recommended Fertilizers for Potatoes

Selecting the right fertilizer sets your potatoes up for success. Here are a few tried and true options:

  1. 5-10-10 Tomato & Vegetable Fertilizer: With its 5-10-10 ratio, it’s excellent for potatoes. The higher phosphorus and potassium levels promote stronger roots and tubers without overloading on nitrogen.
  2. Espoma Organic Garden-Tone 3-4-4: While this has a lower phosphorus and potassium content, it’s still a viable option for early growth stages and offers the benefits of being organic.
  3. Jobe’s Organics All-Purpose Fertilizer 4-4-4: This balanced fertilizer provides equal parts of all three nutrients and is especially good for container or raised bed potatoes.
  4. Miracle-Gro Water Soluble Plant Food 18-18-21: If you need a quick nutrient boost, Miracle-Gro’s water-soluble option can be sprayed directly on plants, but be cautious of its high nitrogen content.

Fertilize Potatoes with a Home-Made Fast Release Fertilizer

How to Fertilize Potatoes with a Home-Made Fast Release Fertilizer

If you like to make your own fast-release fertilizer, by now you know that you will need a low nitrogen one, so, you can choose between a manure tea (but use chicken or horse, the others can be too high in N), or a banana peel brew.

The first is very easy; just put the manure in a bucket (2/3), cover it with water (full) , wait for 10 to 15 days, and scoop the top liquid. Mix one part to 10 parts of water, and then refill the bucket. Be aware that it gets stronger and stronger as time goes by.

However, I would suggest you add a cup per gallon of something rich in potassium, like kelp, greensand or hardwood ashes… That will really plump up your tubers.

If you choose the second, you won’t need to add any potassium, instead, you can add some kitchen waste and some ashes, to give your potatoes a complete meal. Also, if you want to produce it faster, add a tablespoon of molasses…

This too is simple to make. Collect banana peels, put them in a bucket, add kitchen waste (I suggest in equal parts) and ashes, then the molasses, stir well and cover with a cloth. In a week it will be ready…

The timing is the same as with an off-the-shelf fertilizer; start after 2 to 4 weeks, and then every 2 to 4 weeks diluted in 10 parts of water.

When To Stop Fertilizing Your Potatoes

How to Fertilize Potatoes: The Secret for a Bumper Potato Harvest! 3

As the season comes to a close, it’s time to ease up on feeding your potatoes. About two or three weeks before you plan to harvest, stop adding fertilizer. This will help prevent the tubers from rotting and ensure they’re in great shape when you dig them up.

Also, stop watering your potatoes about two weeks before harvest. Harvesting is much easier when the soil is dry, and it also helps prevent the crop from rotting in the ground late in the season.

A Final Tip…

You can still supplement your potato diet with light doses of compost in the meantime; it will help balance their diet and give some slow-release nutrition, also in case you forget, but by now, you also know that adding some greensand or kelp to it, will boost their root growth, and it will give you a much bigger harvest!

Feed Your Potatoes Well and They Will Feed You a Lot!

As I said before, your potatoes need feeding before they feed you. On the other hand, all they eat is cheap and readily available. You can choose an easy option, like compost and an off-the-shelf slow-release fertilizer later on, and, if you come across some kelp, add it as well. So, I’ll leave you to prepare their dinner, and enjoy your bumper harvest later on…

Adriano Bulla

Written By

Adriano Bulla

After many years as an academic in London, Adriano Bulla became a writer, publishing books like A History of Gardening, Organic Gardening and Elements of Garden Design; he then decided to become a gardener, following his childhood dream, and has been following his dream writing and gardening professionally in Southern Europe, where he has specialized in new and innovative organic gardening fields and techniques, like permaculture, regenerative agriculture, food forests and hydroponics.

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