There are three main nutrients that plants need to grow and thrive: Nitrogen, Phosphorus, and Potassium (think back to high school chemistry and remember that “K” is the symbol for potassium). All commercially packaged fertilizers have a set of numbers that correspond with these elements–those numbers indicate the percentage of that nutrient.
10-10-10 contains 10% nitrogen, 10% phosphorus, and 10% potassium
16-16-8 contains 16% nitrogen, 16% phosphorus, and 8% potassium
21-0-0 contains 21% nitrogen and no phosphorus or potassium
When a fertilizer contains all three elements, it is called a “complete fertilizer.”
What balance of nutrients to add depends on your soil. In this article I will assume that you are using a soil mix of compost, peat moss, and vermiculite.
Nitrogen is essential for lush, green vegetation. But be careful–add too much and you’ll get lots of leaves and no fruit! Potatoes, corn, and onions need LOTS of nitrogen (about 4x’s what other vegetables require), while peas and beans need less.
Phosphorus promotes healthy root growth, flowering, and fruit. When there is an extreme deficiency, the leaves will turn purple, but moderate deficiencies result in small plants and stunted growth. This element is less available during cool temperatures, so it may be important to add it early in the spring.
Potassium promotes thick, sturdy stems in fruiting plants and higher yields from root vegetables. A deficiency leads to long, spindly stems and weak plants. This element is less available during cool temperatures, so it may be important to add it early in the spring.
Besides these major nutrients, plants need several trace elements to grow well–like calcium, zinc, iron, boron, and manganese. Zinc and iron deficiencies cause the leaves to turn yellow or tan in between dark green veins.
Putting it all together
My recommendation for those using Mel’s mix is to combine 1 cup of 16-16-8 complete fertilizer with 1/4 cup of Ironite mineral supplement. Sprinkle and mix into the top 6-8 inches of soil before planting in the spring.
Be sure to purchase plant fertilizer instead of slow release lawn fertilizer. It is much less expensive to purchase bulk–either keep it for years to come, or divide among some gardening friends.
|1/3 cup||4′x4′||16 sq ft|
|2/3 cup||4′x8′||32 sq ft|
|1 cup||4′x12′||48 sq ft|
For those who prefer to fertilize only with organic materials, you have lots of options. I love Jerry Baker’s Backyard Problem Solver and Giant Book of Garden Solutions. He includes tons of home made recipes to help in the garden.
There are also commercially available organic sources–blood meal (N), fish meal (N), mushroom compost (P), bone meal (P), seaweed (K), and wood ashes (K) are some examples. Just combine them in the same proportions listed above, and fertilize away!
Another obvious choice is to create and add compost to the garden. Just a quick word of warning–if you add organic materials that are not yet decomposed they can create a shortage of nutrients in the garden. But if you allow microorganisms to work their magic, your grass clippings, food scraps, leaves, and manure can be a gold mine!