How To Fertilize Potatoes

If you want a great potato crop, you need to know how to fertilize potatoes correctly. Getting the nutrients right is the secret to lots of big, healthy spuds under each plant. It’s not hard, but it does require some planning and the right materials at the right time. This guide will walk you through everything, from soil prep to the final feed before harvest.

Fertilizing potatoes isn’t a one-time job. It’s a process that supports the plant through its key growth stages. The goal is to encourage strong roots, vigorous leafy growth, and finally, the development of the tubers themselves. A balanced approach prevents problems and maximizes your yield.

Understanding What Potatoes Need

Potatoes are heavy feeders. They need a good supply of three primary nutrients: Nitrogen (N), Phosphorus (P), and Potassium (K). Each one plays a different role.

Nitrogen (N): This fuels the growth of the green, leafy vines. Too little, and plants are stunted. Too much, and you get huge plants with very few potatoes.
Phosphorus (P): Essential for strong root and tuber development. It helps the plant establish itself and form those initial spuds.
Potassium (K): Sometimes called potash, it improves overall plant health, disease resistance, and the quality and size of the potatoes.

A soil test is the best starting point. It tells you what your soil already has, so you don’t waste money or create an imbalance.

Best Fertilizer Types for Potatoes

You can use organic or synthetic fertilizers. Both work, but they feed the soil and plant in different ways.

Organic Options: These include compost, well-rotted manure, bone meal (for phosphorus), and kelp meal (for potassium). They release nutrients slowly and improve soil structure.
Balanced Synthetic Fertilizers: Look for a formula where the second and third numbers (P and K) are higher than the first (N). A ratio like 5-10-10 or 10-20-20 is often recommended for potatoes.

Many gardeners use a combination, like mixing compost into the soil at planting and then using a balanced organic granular fertilizer as a side dress later.

Step-by-Step Fertilizing Guide

Follow these steps to feed your potatoes from planting to harvest.

Step 1: Preparing the Soil at Planting

This is the most critical application. Work the soil well, removing rocks and clumps. Then, add your amendments.

Mix in 2-3 inches of compost or aged manure across the bed.
If using a granular fertilizer, apply it in the trench or hole before placing the seed potato. Follow package rates, but a general guide is about 1/2 cup of a 5-10-10 fertilizer per 10-foot row.
Cover the fertilizer with an inch of soil before setting the seed potato. This prevents direct contact which can burn the sprouting eyes.

Step 2: The First Side Dressing

When plants are about 6 inches tall, they need a nitrogen boost for vine growth. This is called “side dressing.”

Scrape back a little soil from the base of the plant to form a shallow trench in a circle, about 4 inches from the stem.
Sprinkle a nitrogen-rich fertilizer, like blood meal or a balanced organic blend, into the trench. Use about 1 tablespoon per plant.
Cover the trench back up with soil and water it in well.

Step 3: The Second Side Dressing at Hilling

When you hill soil around the plants (when they’re 8-12 inches tall), it’s time for another feed. This one supports tuber formation.

Use a fertilizer higher in potassium now, like a 0-0-60 muriate of potash or a organic potato fertilizer. Sprinkle it lightly on the soil before you pull the hills up around the plants. Water thoroughly after hilling. This step really helps with yield and skin quality.

Step 4: The Final Boost (Optional)

As plants begin to flower, tuber bulking is in full swing. A liquid feed with a high-potassium fertilizer, like compost tea or a liquid seaweed mix, can give them a final push. Apply it to the soil around the plants according to the bottle’s instructions. Stop all fertilizing once the plants start to yellow and die back, as the tubers need to mature.

Common Mistakes to Avoid

Even with good intentions, its easy to make a few errors. Here’s what to watch out for.

Over-fertilizing with Nitrogen: This is the biggest mistake. Lush, dark green, giant plants with few potatoes is the classic sign. Stick to the recommended amounts.
Fertilizing Too Late: Adding nitrogen late in the season keeps vines growing when they should be senescing, delaying tuber maturity.
Ignoring Soil pH: Potatoes prefer slightly acidic soil (pH 5.8 to 6.5). If your soil is too alkaline, nutrients get locked up. Soil test results usually include pH.
Not Watering After Feeding: Granular fertilizers need moisture to dissolve and move into the root zone. Always water after applying any dry fertilizer.

Signs of Nutrient Problems

Your plants will tell you if something is off. Learn to read the signs.

Purple Leaves or Stems: Often a sign of phosphorus deficiency, especially in cool, wet springs.
Yellow Lower Leaves: Could be a nitrogen deficiency, especially if it starts at the bottom of the plant and moves up.
Brown Leaf Edges or “Scorching”: Can indicate a potassium deficiency or sometimes over-fertilization.

Correcting deficiencies quickly is important. A foliar spray with a diluted liquid fertilizer can provide a fast fix for some issues.

FAQ: Fertilizing Potatoes

What is the best natural fertilizer for potatoes?

A mix of compost, bone meal, and kelp meal or greensand provides a excellent natural nutrient balance. Well-rotted chicken manure is also very effective but must be composted first to avoid burning plants.

Can I use just compost to grow potatoes?

You can, and you’ll get a crop. But for a truly bountiful harvest, compost alone often doesn’t provide enough phosphorus and potassium. Supplementing with other organic amendments is usually necessary for best results.

How often should you fertilize potato plants?

Typically, three times: at planting, at 6-inch height, and at hilling. A possible fourth liquid feed at flowering can be beneficial. Avoid fertilizing after vines begin to die back.

Is Epsom salt good for potatoes?

Epsom salt provides magnesium and sulfur. It can be beneficial if your soil is deficient in magnesium, which a soil test can reveal. Otherwise, it’s usually not necessary. Don’t rely on it as a main fertilizer.

What fertilizer makes potatoes bigger?

Adequate potassium (potash) is crucial for tuber size and quality. Ensuring a good supply at tuber initiation (during hilling) is key. Consistent watering during bulking also directly impacts size.

Mastering how to fertilize potatoes takes the guesswork out of growing. By focusing on soil prep, using the right nutrients at the right stages, and avoiding common pitfalls, you set the stage for success. Your reward will be a generous harvest of homegrown potatoes, perfect for storing and eating all season long. Remember, healthy soil grows healthy plants, so each year you improve your soil, you make next year’s crop even better.