When Should You Fertilize Potatoes?
The best time to fertilize potatoes is before you plant them. This gives the potato plants a chance to absorb the nutrients they need before they start growing. For early-season potatoes, apply 2/3 of the total nitrogen needed for the season before planting.
Then, split the remaining fertilizer into 2 or 3 biweekly applications starting 6–7 weeks after planting. These should be in the form of side-dressing to prevent root damage.
For medium- or late-season potatoes, apply 1/3 of the fertilizer before planting and split the rest according to the instructions above. Now you know how to use fertilizer for potatoes! But what should it contain? Read on to find out.
What Nutrients and Micronutrients Do Potato Plants Need?
Before planting, a balanced fertilizer for potatoes (with an NPK ratio of 15-15-15) will do the trick. Later, your potato plants will need fertilizers with dominant nitrogen and potassium. Nitrogen helps the plant to grow leaves, while potassium regulates the amount of water in the tubers.
Some phosphorus is also needed for tuber growth. In addition, potato plants need micronutrients like magnesium, zinc and calcium. These can be found in fertilizers formulated for potatoes, or you can use a separate fertilizer for each one.
What Soil pH Is Ideal for Potatoes?
Potatoes like slightly acidic soil with a pH of between 6 and 6.5. You can test your soil’s pH level with a kit from your local garden center. If the pH is too high, you can add sulfur to lower it. If the pH is too low, you can add limestone to raise it.
Best Fertilizer for Potatoes – After Planting
Growing potatoes is a bit different from other vegetables. For one, you don’t need to fertilize them shortly after planting. Wait a month or two before applying a high-nitrogen fertilizer (e.g., 34-0-0). This will encourage the potato plants to grow leaves and start photosynthesizing.
As we mentioned before, you should split the fertilizer into 2 or 3 applications after planting. This is important because too much nitrogen at once can damage the potato plants and pollute the groundwater. Apply the fertilizer to the soil, not the foliage, and water it in well.
You can also opt for a slow-release fertilizer. This fertilizer for potatoes releases nutrients over a period of time, so you don’t have to fertilize as often. Just be sure to read the label carefully to find out how often you need to apply it.
You probably won’t find nitrogen-rich fertilizers formulated for potatoes specifically, but during this phase of growth, lawn fertilizers will work just fine. Look for fertilizer with an NPK ratio similar to 25-0-2, 30-0-0 or 35-0-0, and apply it according to the instructions on the package. Here are two examples:
- Scotts Turf Builder Lawn Food;
- Pennington UltraGreen Lawn Fertilizer.
Best Fertilizer for Potato Plants – Before Harvest
The last couple of months before harvest are when your potato plants need potassium the most. This element helps to regulate water in the tubers and prevents them from shrinking. It also strengthens the plant’s resistance to disease. An NPK of 12-12-17 or 14-7-21 should work great.
You can side-dress potato plants with a fertilizer that contains potassium, or you can use slow-release fertilizer. If you opt for the latter, make sure to apply it a few months before harvest so that the plants have time to absorb the nutrients. Here are some good options:
- Vitax Organic Potato Fertilizer;
- NPK 12-12-17 Grandfield Adfert Fertilizer;
- Organic Kelp Fertilizer by GS Plant Foods.
Now you know everything there is to know about the best fertilizers for potatoes! Just remember to split it into several fertilizer applications (one before you plant potatoes and 2–3 after) and water it in well after each one. This will ensure that your potato plants are healthy and productive throughout the growing season. If you’re unsure what to use, do a soil test.
Have you found a good fertilizer for potatoes? Share your choice in the comments below!
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