Instead of buying plant food for fertilizing your houseplants, try amending ordinary potting soil with Epsom salt and coffee grounds. Epsom salt supplies magnesium and lowers the pH of potting soil, making it easier for plants to absorb other nutrients. Coffee grounds help plants absorb nitrogen. Using one or both is safe for your plants, pets and children and saves you money on fertilizer. In addition, using coffee grounds helps you recycle some household waste that might otherwise just get thrown away. There is more than one way to apply each of these natural fertilizers. Measure 1 teaspoon of Epsom salt for each foot of plant height. Sprinkle it directly onto the surface of the potting soil of the houseplant. Water the plant after applying the Epsom salt so the nutrients can sink into the soil. Repeat every week. Pour a tablespoon of Epsom salt into a gallon of water and mix well. Spray the solution onto the foliage of your plants and onto the surface of the potting soil. Both roots and leaves will absorb the nutrients. Repeat every several weeks.
Sprinkle coffee grounds on the surface of the potting soil at the base of a plant. Because the microorganisms that break down coffee grounds use nitrogen, sprinkle a nitrogen fertilizer over the coffee grounds for the plant to use while the microorganisms are active. Otherwise the plant may be deprived of sufficient nitrogen. Use a garden trowel to scratch both the grounds and the fertilizer into the soil. Be careful not to damage plant roots.
Spread coffee grounds on the surface of potting soil around the base of a plant to repel insects and slugs. Cover the grounds with a mulch of leaves, bark or compost — if the coffee grounds dry out they could repel water. Renew the coffee grounds and mulch whenever necessary. A few tips many coffee shops give away free coffee grounds for gardening purposes. Use Epsom salt and coffee grounds to amend the soil in outdoor gardens as well as for potting soil for container plants.