How much fertilizer do I add?
Labels give a dose "per gallon" - but your watering can isn't a gallon, and most houseplants do better on a weaker mix. Enter what the bottle says and your can size to get the exact amount, at the strength you want.
Half strength - a safe everyday default for most houseplants.
How to use it: water the plant first if the soil is bone dry, then apply the diluted feed to damp soil until it drains from the bottom. Stir or shake well so it's evenly mixed.
Underfeeding is easy to fix - overfeeding burns roots. When in doubt, go weaker and feed more often. Flush the pot with plain water every 4-6 weeks to clear salt build-up, and don't feed dormant or stressed plants.
How to dose fertilizer for houseplants and garden plants
This calculator is for liquid and water-soluble feeds that you mix into water, for houseplants and garden plants; it is not written for aquarium plants. How strong a mix and how often depend on the plant. Here is what extension services say for some common ones, so you know what to enter as the strength. In the garden, start from a soil test.
| Plant | What to use | How strong and how often | Source |
|---|---|---|---|
| Peace lily | Balanced liquid houseplant fertilizer, such as 20-20-20 | One-quarter of the recommended strength, every 6 to 8 weeks in spring and summer | Clemson |
| Indoor ferns | Liquid houseplant fertilizer | About half the recommended rate, once a month from April to September; none in winter or for six months after repotting | Clemson |
| Rubber plant | Water-soluble houseplant fertilizer | Every two weeks in spring and summer; less often in lower light | Clemson |
| Jade plant | Liquid houseplant fertilizer | Once every three to four months; wait four months after repotting | Clemson |
| Philodendrons | Dilute water-soluble houseplant fertilizer, or a time-release one | Regularly; too much makes leaf tips curl and brown | Clemson |
| Tomatoes (garden) | Granular complete fertilizer, such as 8-8-8 or 10-10-10 | 2 to 3 tablespoons per plant once fruit sets, then every 4 to 6 weeks, kept 4 to 6 inches from the stem | NC State |
| Bigleaf hydrangea | Granular 10-10-10 | 2 cups per 100 square feet in March, May and July | Clemson |
| Peonies | Low-nitrogen 5-10-5 or 5-10-10 | 2 to 3 pounds per 100 square feet in spring, when the stems are 2 to 3 inches high | Clemson |
| Onions | 10-10-10, then 5-10-10 and calcium nitrate | Without a soil test: 9 pounds of 10-10-10 per 1,000 square feet before planting, then two side-dressings as the bulbs swell | Clemson |
The granular rows are not for this calculator: weigh or measure them as written. For a liquid feed, enter the dose from your label and pick the strength from the table, for example a quarter for a peace lily or a half for a fern.
This is a dilution helper, not feeding advice for a specific plant. Always follow your fertilizer's own safety directions, and remember that "less, more often" beats one strong dose. Liquid and granular products differ - this tool is for liquid/water-soluble feeds you mix into water.
For measuring the dose
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