potatoes growing in compost

Can I Grow Potatoes In Straight Compost: + how to increase its P and K

You may have read about growing potatoes in compost and wondered if it was really a good idea. Technically, potatoes can be grown in compost alone, but it isn’t always the best choice. Amending your soil with compost or making a potting mix with compost and soilless mix for containers may be a better choice.

Do you grow potatoes in soil or compost?

Potatoes can be grown in either soil or compost but are typically grown in soil that has been amended with compost. Sometimes, compost and soil are combined and then used in containers for growing potatoes.

Potatoes grown in the garden prefer sandy, well-drained soil with a pH between 6 and 6.5, explains the University of Minnesota Extension. Adding compost to your existing soil improves drainage, provides slow-release nutrients, and improves aeration.

However, garden soil is not recommended for potatoes grown in containers as it compacts easily when watered, dries out quickly, and may contain weed seeds. The University of New Hampshire recommends one part soilless mix (or peat moss) and one part compost for growing potatoes in containers.

Can you grow potatoes in just compost?

Some report success with growing potatoes in compost bags filled with compost, but it is not the best way to grow potatoes. Because compost is usually as high in nitrogen as it is in phosphorus and potassium it poses a high risk of producing a potato plant with large foliage/leaves with only small potatoes under the soil.

Even though potatoes are heavy feeders and require more fertilizer than other garden veggies, they need to have fertilizer in the correct ratio. Potatoes grown in compost alone will likely grow oversize tops, resulting in tall, weak plants that break or flop easily from wind and rain.

Weak plants will produce tubers, but they will likely be smaller, and your yield will be low.

What is the NPK value of regular compost?

The NPK value of compost varies depending on whether your compost is made up primarily of kitchen and yard wastes or if it contains animal manures. Typical compost made from kitchen and yard wastes has an NPK ratio of  2 percent nitrogen (N), .5 to 1 percent phosphorus (P), and  2 percent potassium (K), giving it a ratio of 2-.5-2 or 2-1-2, says Britannica.

Compost from animal manures, particularly chicken and rabbit manure, may be considerably higher in nitrogen, especially if the compost isn’t fully mature.

Are there different types of compost?

Traditional Compost

This is the compost from a backyard compost pile or compost bin. It is typically made from kitchen scraps and yard and garden wastes. You can also buy traditional compost in bags at garden centers and hardware stores.

Farmyard Manure Compost

Manure compost is made primarily from horse, cow, or chicken manure. It may include other farmyard animal manures, such as goats or rabbits. This manure generally contains high amounts of nitrogen and is nutrient-rich. It may burn the roots of plants or may cause excessive foliage growth with reduced fruiting.

Green Manure Compost

Green manure is a cover crop of legumes grown when the soil is fallow. These crops break down into the soil at the end of the season as the plants decompose that add natural compost to the soil. Green manure benefits rice, sugarcane, wheat, and corn, explains Luxury Landscape Supply.

Vermicompost

Vermicompost is made by adding earthworms to the decomposing matter. Earthworms help to break down the organic matter and add worm castings to the soil. Vermicompost provides a highly concentrated source of nutrients. To use vermicompost, use one-third the amount you would of traditional compost, says Common Compost.

What is the best compost to grow potatoes in?

Traditional compost is usually the best compost to grow potatoes in. It is dark and rich and smells like fresh soil because all the organic matter has decomposed. It provides a good source of organic matter to the soil. Organic matter is rich in nutrients and improves the texture of the soil. It improves both drainage and water retention while providing plenty of aeration to your plant’s roots. Potatoes can be grown in traditional compost alone, but it is always best to mix compost with the existing soil when growing potatoes.

How can I add more P and K to compost to grow potatoes?

Like other plants, potatoes need adequate amounts of nitrogen, phosphorus, and potassium to thrive. Understanding how each nutrient affects the growth of your potatoes will help you decide when and if you need to add additional nutrients when using compost.

  • Nitrogen: Nitrogen is responsible for both stem and leaf growth. It is necessary for healthy plant growth and gives the foliage a bright green coloring.
  • Phosphorus: Phosphorus helps to produce the tubers. It affects the overall yield, size, and health of the potato tubers. Dark green or reddish-purple along the edges of leaves and lack of new shoots are signs of a phosphorus deficiency.
  • Potassium: Potassium also helps sustain a good yield. It also reduces black spots on potatoes. Signs of a potassium deficiency include browning and curling edges on the leaves and yellowing between the veins of the leaves.

How to Add Phosphorus (P) to the Soil

Compost is a good source of phosphorus for your potato plants and is often used as a soil amendment to increase phosphorus in the soil. However, you can add more phosphorus with several products found in gardening centers and hardware stores.

  • Bone Meal: Bone meal is made from ground-up animal bones and provides a fast-acting source of phosphorus for your soil.
  • Rock Phosphate: Rock phosphate is slower acting than bone meal. It is best to add rock phosphate in the spring so that it has time to work.
  • Phosphorus Fertilizer: Look for a fertilizer with a high phosphorus content, with the middle number being the highest in the NPK ratio.

How to Add Potassium (K) to Soil

There are several products you can use to add potassium to the soil. Most are readily available at your local home improvement center or hardware store. Follow the application rate on the container.

  • Greensand: Greensand is a natural soil amendment made from marine deposits. Because it is sandy, it may be best used in soils high in clay content.
  • Potassium Sulfate: Potassium sulfate may be either organic or manufactured and is readily available in garden centers.
  • Alfalfa Meal: Alfalfa meal is an excellent organic source of potassium, but it is slow-release and takes longer to begin working. If you choose alfalfa meal, apply it in the early spring, so it has time to work its magic when your potatoes need it.

Summary

There is no doubt about it; compost is good for your potatoes as it provides many nutrients they need to thrive and improves your soil too. Whether you amend the existing soil with compost or use soilless compost is up to you. Try it out for yourself, grow potatoes side by side in the two different mediums to compare how they grow.