You can buy ready-made plant fertilizer from your local nursery, but if you want to save money and know exactly what’s in the concoction, you can make your own from household ingredients.

First, let’s talk about what nutrients plants need from the soil, also known as mineral nutrients. (Plants get non-mineral nutrients, including hydrogen, carbon and oxygen, from air and water). Mineral nutrients can be divided into two categories: macronutrients and micronutrients. The primary macronutrients a plant needs are nitrogen, phosphorus and potassium. Then there are secondary macronutrients such as calcium, magnesium and sulfur. Most fertilizers have a balanced combination of the three primary macronutrients to be effective. In your homemade fertilizer, you are recreating that balance.

Before you do anything, test your soil to see what nutrients it contains naturally. (Don’t know how? You can buy a soil test kit, or try this quick and easy way.) The results of the soil test will help you make decisions around how to fertilize. For example, if your soil is low on potassium, using banana peels in your garden can help. (More on that later.)

You should also test the pH, as the levels of those primary macronutrients in your soil and your plants' absorption of them varies depending on the pH. The ideal soil pH level ranges from 6.0 to 7.0. If your soil's pH is low, it's acidic, and if the pH is high, it's alkaline. Add lime to acidic soil to make it more alkaline, and add elemental sulfur to make alkaline soil more acidic. In neutral soil, plants will generally take up nitrogen more quickly, leading to better growth.

It’s important to know what you’re working with before you start creating your own mixture. Once you do, here are some elements to try:

Banana peels: Your doctor may have told you to eat a banana a day if you’re low on potassium. The high concentration of potassium in bananas can help your plants grow too. There are a number of ways to use a banana peel in your garden, and it’s a great addition, particularly if you’re growing roses.

Compost: if you don’t already have one, consider starting a compost pile, which consists of both green matter (organic waste such as food scraps) and brown matter (dead leaves, sticks). Once you add water, it allows the material to break down and the nutrients from the organic waste to become absorbable. If you spread aged compost around the base of your plants, it will help keep your soil moist.

Coffee grounds: Used or fresh coffee grounds can fertilize your garden. Fresh coffee grounds, which have a lower pH than used coffee grounds, can be used as fertilizer for plants that thrive in acidic environments, like azaleas, hydrangeas and lilies, or root vegetables, like carrots or radishes. Toss used coffee grounds (and coffee filters) into your compost bin to add nitrogen and to aid with decomposition.

Sprinkle crushed eggshells around the base of your plants to provide calcium. Sprinkle crushed eggshells around the base of your plants to provide calcium. (Photo: ThamKC/Shutterstock)

Eggshells: Eggshells are a great source of calcium for your plant garden. Just wash them, crush them up into a powder using a blender and sprinkle around the base of your plants.

Pee: That’s right — urine from a healthy person is sterile and has many nutrients that can be beneficial to plant growth. Because urine is very concentrated however, be sure to dilute it before you apply it to your plants, otherwise it can burn them. Generally, you should use 20 cups of water for one cup of urine and then pour it around the base of your garden.

Epsom salts: Epsom salts, a naturally derived mineral salt from England, have been used for years to help treat various illnesses. It can also help your plants. How so?

From the National Gardening Association:

Chemically, Epsom salts is hydrated magnesium sulfate (about 10 percent magnesium and 13 percent sulfur). Magnesium is critical for seed germination and the production of chlorophyll, fruit, and nuts. Magnesium helps strengthen cell walls and improves plants' uptake of nitrogen, phosphorus, and sulfur.

Happy planting!