Liquid Fertilizer For Potatoes: pros, cons, and how to choose

Fertilizing your potatoes during the growing season keeps them healthy and promotes a good yield. Many chose to apply granular fertilizer to the soil before planting them and side-dress the potatoes two weeks after planting them and then once a month up until two weeks before harvesting. But you don’t need to fuss with granular fertilizer. You can use liquid fertilizer on your potatoes instead.

What are the benefits of using liquid fertilizer for potatoes vs. granular?

Liquid fertilizer, also called foliage feeder, is quick and easy to apply and begins working immediately. Because liquid fertilizer is mainly used on potato plants that have already emerged through the soil, the nutrients in liquid fertilizer are absorbed through their leaves. This leads to a very fast uptake compared to granular fertilizers which are slow release. In fact, you may notice your potato plants ‘greening up’ within a day or two.

Granular fertilizer needs time to dissolve in the soil to make the nutrients available to the roots of your plants. So while it can be relatively quick-acting, it doesn’t provide nutrients immediately.

  • Plants absorb it through the leaves.
  • Quick Acting
  • Easy to Store
  • Easy to Mix
  • Easy to apply

What are the negatives of using liquid fertilizer for potatoes?

  • Requires some form of applicator/ sprayer
  • It may require a long garden hose
  • Leaves foliage wet — wet foliage at night can promote disease.
  • Fewer formulas to choose from
  • More expensive to use

What should I look for when choosing a liquid fertilizer for potatoes?

Potatoes need a fertilizer formula that is lower in Nitrogen (N) and higher in Phosphorus (P) and Potassium (K) when you first plant them in the spring. It is recommended to use a ratio of (5-10-10) because too much nitrogen causes potato plants to grow rapidly and become overgrown or weak, at the expense of poor tuber growth. This is a rough guide to the fertilizer requirements for growing potatoes – it is much better to take a soil sample and find out exactly what your crop needs.

Early fertilizing typically involves adding granular fertilizer and mixing it into the soil before you plant your potatoes. This gets the potatoes off to a good start. However, if you use a liquid fertilizer high in P or even a straight P formula, you will notice that your potatoes will come through the ground much faster than if you use a granular fertilizer of the same ratio. Phosphorus (P) promotes root development so it is a good idea to use enough at planting. If you have already used granular at planting you can apply liquid fertilizer to the plants once they are 4 to 6 inches tall.

According to Bob Villa, potatoes need a formula with more nitrogen during the middle of the growing season and thrive with a high amount of potassium in the last two months of the growing season. Potassium (K) is needed to bulk out your potatoes as they near the last third of their growth.

Neptune Harvest Tomato and Veg formula has an NPK ratio of 2-4-2 and is suitable for use at planting as it is high in Phosphate which gets root establishment underway quickly.

Miracle-Gro Aero Garden liquid fertilizer has an NPK ratio of 4-3-6 and is a good choice for mid-season or the last two months of plant growth.

When should I apply liquid fertilizer to potatoes?

The application rate and timing of applying liquid fertilizer depend on the specific product. Neptune Harvest is higher in P so should be used at the start of the season whereas Miracle-Gro is higher in N and K which makes it more beneficial to be applied from mid-season onwards. The final thing to remember is you should apply fertilizer when the crop needs it – it’s important not to over-fertilize as this can cause issues with massive potatoes with hollow hearts.

Always follow the application rate on the container and apply as directed when using liquid fertilizer.

Where should liquid fertilizer be applied to potatoes?

Most liquid fertilizers are designed as foliar feed and work best when applied to the foliage of your plants. Spraying the entire plant so that you wet the foliage ensures that the leaves will begin absorbing nutrients immediately. The roots of your potato plants will also absorb nutrients in the solution that runs into the soil.

While you can apply the solution at the soil level and let it sink in to provide your potatoes with a boost of nutrients, wetting the foliage with the liquid fertilizer is often more effective, unless you are applying the fertilizer at planting to speed up their establishment.

Always double-check that the liquid fertilizer you purchase is safe to apply to the leaves of your potato plants. While most liquid fertilizers are also foliar feeders, some are not.

What equipment do I need to apply liquid fertilizer?

Liquid fertilizer is typically applied with a sprayer. This can be a tractor sprayer, a knapsack sprayer, or a handheld bottle sprayer. Many fertilizer companies also produce smaller hose-end sprayer attachments that automatically mix the fertilizer with water as you spray your plants. If you choose this method, you will need a hose long enough to reach all your potatoes comfortably and a hose-end sprayer. Both can be purchased at gardening centers or your local hardware store.

a sprayer can apply liquid fertilizer
In smaller areas a knapsack sprayer can be used to apply liquid fertilizer.

Liquid fertilizer can also be mixed with water in a 5-gallon bucket and used to water your potato plants. If you choose this method, you will need a 5-gallon bucket, a watering can, or another container to dip and pour the liquid fertilizer.

Do you need to mix the liquid fertilizer?

You can buy premixed liquid fertilizer, but most come in a water-soluble formula to be mixed with water as you need it. This formula is granular or liquid and needs to be measured and mixed according to the manufacturer’s instructions. Most provide a convenient measuring spoon with the formula. If you are using a hose-end sprayer, the appropriate amount of granules is added to the hose-end sprayer reservoir. As water from the hose travels through the sprayer, it automatically mixes liquid fertilizer to the correct strength.

Can I make liquid fertilizer for potatoes at home?

You can make homemade liquid fertilizer easily in the backyard but beware. This homemade liquid fertilizer is not a foliar feeder and must be applied to the soil. In addition, it will burn the leaves if you apply it directly to your potato plants, warns GrowVeg.

  1. Pour one gallon of water into an old bucket or pail.
  2. Add one cup of well-rotted chicken manure.
  3. Toss in a handful or two of fresh grass clippings.
  4. Mix it well to blend all ingredients.
  5. Cover the pail with a loose cloth and set it in the shade to ferment for 48 hours.
  6. Strain the solution through an old colander or a piece of mesh.

To use the homemade liquid fertilizer, mix the solution with five parts water before applying it to the roots and soil around your potato plants. Also, take a look at this alternative homemade potato fertilizer.

What NPK ratio should liquid fertilizer for potatoes be?

The best NPK ratio of liquid fertilizer for potatoes depends on the condition of your soil, your plant’s health and growth rate, and the time of year you are applying it. Assuming you have a healthy balance of nutrients in your existing soil, a balanced or nearly balanced formula will work well throughout the season.

However, a potato plant’s nutritional needs also change during the growing season. While too much nitrogen at planting time can result in large, showy potato plants with few tubers, potato plants need enough nitrogen to promote healthy growth. Generally, a ratio of 5-10-10 is a good ratio for potato fertilizer, this ratio is backed by the University of Wisconsin Extension

The best way to determine which nutrients your soil needs is by performing a soil test in the spring before planting your potatoes, so you will know if your soil contains a balance of nutrients.


Using liquid fertilizer on your potatoes is quick and easy, you can apply it while watering them or when applying other sprays such as a blight spray. The speed at which your potato crop responds to liquid fertilizer is truly amazing. Most home gardeners find success with using a balanced formula all summer long, but there may be times when you need to adapt to the needs of your potatoes. Use your soil test results and the health of your potatoes as a guide to choosing the right liquid fertilizer for your garden. Try using liquid fertilizer on your next crop of potatoes to experience its effects for yourself.