How to Make Natural Magnesium & Potassium for Plant Food

Updated February 21, 2017

All plants need potassium and magnesium to be strong and healthy. Potassium, like nitrogen and phosphorus, is one of the three primary macronutrients plants need. Magnesium is a secondary macronutrient, meaning that plants do not need nearly as much of it as they do potassium. You can use synthetic fertilisers on your plants, but doing so risks giving the plants too much of a good thing and has environmental impacts. Homemade, natural fertilisers are safer and less expensive to use.

Fill the 5-gallon bucket with about 2 gallons of room temperature water. Add about a pound of sea kelp to the water and cover the bucket.

Let the kelp steep for at least two days.

Strain the kelp from the water by pouring it through the mesh strainer into the second bucket. Don't throw out the kelp; you can dig it into the soil in your garden or lay it on top of the soil for extra fertilisation.

Pour the kelp water into a spray bottle, using a funnel to prevent spills.

Spray the kelp water directly on the leaves of plants to give them a foliar boost of potassium.

Pour 1 tsp of Epsom salts into the bottom of the second spray bottle.

Add 1 quart of water to the bottle. Put the lid on the bottle and shake it to dissolve the Epsom salts.

Spray the Epsom salt water directly on the flower buds of pepper, tomatoes and other nightshades to encourage fruit set.

Double the amount of Epsom salts to 2 tsp per quart of water and spray on houseplants to fertilise them every month.

Things You'll Need

  • 5-gallon bucket with lid
  • Kelp meal or fresh sea kelp
  • Water
  • Mesh strainer
  • Additional bucket
  • Funnel
  • 2 spray bottles
  • Epsom salts
  • Measuring spoons and cups
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About the Author

Based in Pennsylvania, Emily Weller has been writing professionally since 2007, when she began writing theater reviews Off-Off Broadway productions. Since then, she has written for TheNest, ModernMom and Rhode Island Home and Design magazine, among others. Weller attended CUNY/Brooklyn college and Temple University.