Plants need light, water, and nutrients. Most plants get their nutrients from the soil, but over time a soil’s nutrients can get depleted, especially with potted plants. This is when fertilizer comes in handy. But there are a few things you should know about fertilizer before feeding your plant.
Most commercial fertilizers include 3 main nutrients: nitrogen, phosphorus and potassium (NPK for short). These are often listed as numbers on a fertilizer’s packaging, in the form of 10-20-15 or 15-15-15. The numbers correspond to the percentages of N-P-K in the fertilizer. All purpose fertilizer usually has them in equal proportions, but the labeling should be clear. There are special fertilizers for plants like orchids or roses that have different proprotions of NPK and other micronutrients the plants might need, and there are even fertilizers for stages of growth (ex: younger plants often need more phosphorous). A fertilizer’s label should tell you all you need to know about what it’s meant to be used for.
Now about when to fertilize: the general guideline is to fertilize during the growing season, which is usually spring and summer. The extra warmth and light during these seasons stimulates plant growth that pauses during the cold and dark of winter. This is also why plants need less water during the winter. Adding nutrients at the right time helps spur that growth.
Something else to note is that it’s very possible to give a plant too much fertilizer. It’s possible to “burn” a plant with too much fertilizer at once, and you’ll notice this if the tips of the leaves turn yellow/brown. Always follow the guidelines that come with the fertilizer you’ve purchased. Some fertilizer is liquid that you mix in when you water the plant, and some comes in solid form you stick in the soil or sprinkle above it.
Also note that new commercial potting mix generally already has fertilizer in it, so you wouldn’t want to fertilize a freshly potted plant right away – wait about a month or so.
That’s about it. Now go forth and feed your hungry plants!