Plants & Potassium: Using Potassium in the Garden

By Heather Rhoades
Published: February 28, 2017 | Last updated: March 2, 2017
Key Takeaways

Providing potassium to plants improves how well they grow and produce, but exactly why and how is not known. As a gardener, you do not need to know the why and how to be hurt by potassium deficiency in plants. Keep reading to learn more about how this macronutrient affects your plants and how to correct a deficiency.

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Effects of Potassium on Plants


Potassium is important to plant growth and development. Potassium helps plants:

  • Grow faster
  • Use water better
  • Be more drought-resistant
  • Fight off diseases
  • Resist pests
  • Grow stronger
  • Produce more crops

So, in other words, when a plant has enough potassium, it will simply become a better plant.


Signs of Potassium Deficiency

It can be difficult to see specific signs of potassium deficiency in plants—plants will simply not perform as well as they should. When severe deficiency happens, you may be able to see some signs in the leaves. The leaves, especially older leaves, may have brown spots, yellow edges, yellow veins or brown veins.

Potassium Fertilizer


Potassium fertilizer is sometimes called potash fertilizer because it often contains a substance called potash, a naturally occurring substance found in wood ash or in mines and oceans. While potash is technically a naturally occurring substance, only certain kinds of potassium fertilizers containing potash are considered organic.

Some products are referred to as high-potassium fertilizers. This simply means they contain only potassium, or otherwise have a much higher amount of potassium than nitrogen or phosphorus. If you wish to add potassium to your soil at home, there are several ways you can do so.


The first is applying a high-potassium fertilizer product. The next way is to use compost. Compost made primarily from food by-products, particularly bananas, is an excellent source of potassium.

Wood ash can also be used, but make sure you apply it lightly, as too much can burn your plants. Greensand, which is available from most nurseries, will also add potassium to you garden.

Because potassium deficiency in plants can be hard to spot simply by looking at the plant, it is always a good idea to have your soil tested before adding fertilizers.

PRO TIP: Using Ashes in the Garden

Wood ash is an excellent source of lime and potassium for your garden. Using ashes in the garden also provides many of the trace elements that plants need to thrive. Wood ash fertilizer is best used either lightly scattered or composted first along with the rest of your compost. This is because wood ash will produce lye and salts if it gets wet.

In small quantities, the lye and salt will not cause problems, but in larger amounts, they may burn your plants. Composting fireplace ashes allows the lye and salt to be leached away.

Not all wood ash fertilizers are the same. If the fireplace ashes in your compost are made primarily from hardwoods, like oak and maple, the nutrients and minerals in your wood ash will be much higher.

If the fireplace ashes in your compost are made mostly by burning softwoods, like pine or firs, there will be less nutrients and minerals in the ash.

Other Uses for Wood Ash

Wood ash is also useful for pest control. The salt in the wood ash will kill bothersome pests like snails, slugs and some kinds of soft-bodied invertebrates. To use wood ash for pest control, simply sprinkle it around the bases of plants that are being attacked by soft-bodied pests.

If the ash gets wet, you will need to refresh the wood ashes, as the water will leach away the salt that makes wood ashes an effective pest control.

Another use for ashes in the garden is changing the pH of the soil. Wood ashes will raise the pH of soil. Because of this, you should also be careful not to use wood ashes as fertilizer on acid-loving plants like azaleas, gardenias and blueberries.

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Written by Heather Rhoades

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Heather Rhoades is the founder of Gardening Know How, where she continues to write articles and answer questions relating to gardening.

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