Soil testing is an important activity for a successful garden. Soil stewardship is an ongoing process, where you test and amend, grow some stuff, then test, amend and grow some stuff….and so on. Focus on building soil tilth so it can really hold and make available to the plants all the important nutrients. You do this in part by adding compost, manure, rock dust, bone meal, kelp & fish emulsions. Read this article series to learn more about each of the 13 key nutrients for your garden.


Potassium is needed by plants for normal growth and high fruit quality. Potassium atoms are positively charged and balance out negatively charged compounds like sulphates, nitrates and chlorides. Potassium is necessary for the plant to manage its transpiration, the process of moving water through the plant and out the pores into the atmosphere, and is also used in opening and closing the stomates, the small holes in the leaves. It is important for creating cell walls.

Plants that are deficient in Potassium will show signs beginning at the oldest leaves, which will develop yellow margins and curl downward while the veins remain green. Fruit will also be impacted, and have a skimpy stem end. Growth will be stunted and leaves will be small. Potassium deficiency tends to cause or worsen an iron deficiency. Legumes may be particularly impacted by having their Nitrogen fixing bacteria produce less Nitrogen due to decreased sugar processed within the plant nodules.

To correct a deficiency of Potassium
  • first ensure that your soil has adequate organic matter and is not too sandy
  • make sure the pH is not too low, as low pH makes it harder for plants to absorb Potassium
  • add kelp, banana peels, greensand and small amounts of wood ash to the soil to add Potassium

Plants with too much Potassium in their soil may have dead leaf margins but Potassium toxicity is rare.

To offset excessive Potassium
  • create a strategy to boost other nutrients, especially Nitrogen without using manure (because manure is very high in Phosphorous)
  • plant beans and peas (legumes) which will fix Nitrogen and make it available to other plants without introducing Phosphorous or Potassium
  • both cucumbers and tomatoes like slightly less Nitrogen versus Phosphorous and could help use up some of the Phosphorous in the soil
  • Root vegetables like parsnips, carrots, beets and radishes all require Phosphorous and Potassium
  • Clover and vetch (do not eat vetch it is poisonous) can be used to balance the nutrients in the soil
  • Design a rotation something like this: Carrots, Beets, Radishes, Clover, Parsnip, Beans, Vetch (do not eat vetch it is poisonous), Peas, Cucumber, Tomato
Copyright © 2015 Lori Wardell