Liquid fertilizer is a good choice for container plants because it reacts more quickly than granular or organic fertilizers and can be applied easily and quickly. A liquid fertilizer application can be done either by attaching a mixing unit to the end of your hose, or by mixing the correct amount of the fertilizer in a watering can or pail and then watering the container plant with the mixture.
A 24-12-10 liquid fertilizer will encourage green growth in plant material grown in fiberglass planters very rapidly because it is high in nitrogen. Nitrogen is the compound that plants need for good foliage growth.
The numbers on a fertilizer label explain what percentage of nitrogen, phosphorus, and potassium are in the fertilizer. The first number refers to the amount of nitrogen, the second to the amount of phosphorus, and the third to the amount of potassium. These ingredients are often abbreviated as N-P-K. (The ‘K’ stands for potassium.) So a 24-12-10 liquid fertilizer is made up of 24% nitrogen, 12% phosphorus, and 10% potassium.
A liquid fertilizer that is high in nitrogen (such as a 24-12-10 mixture) is often used on grass to make it thicker and greener, or on container plants that are mostly leaves. High nitrogen plant food can stress the root systems of perennial plants and shrubbery, but for container plants, it can be useful since container plants don’t generally winter over.
Feeding high nitrogen liquid fertilizer to lawns and grassy areas is coming under increased criticism because of the damage that nitrogen run-off does to rivers and local water tables, but for houseplants or annuals in pots, it is not dangerous.
When choosing a liquid fertilizer it is very important to consider what kind of plant you are feeding. Nitrogen encourages leaf growth and greenery, but phosphorus encourages root and bud growth (for fruit and flowers). Potassium contributes to the overall health of any kind of plant.
For most flowering and fruiting plants, a more traditional liquid fertilizer ratio is 1-2-1 (regardless of how big the numbers are). So a 12-24-10 liquid fertilizer is better for flowers, because the first and last numbers are about half the middle number.
For a general, all-purpose liquid fertilizer, look for any kind with a high middle number (phosphorus), and first and third numbers that are about half of the middle number (for example, 5-10-5, or 10-20-10).
Some liquid fertilizers are created specifically to stimulate root growth. Root stimulating liquid fertilizer commonly has a phosphorus content which is more than double the other two numbers, (such as 4-10-3).
Other liquid fertilizers are labeled ‘organic’ because they have carbon compounds in them that come from plants or animals. An organic liquid fertilizer has the same N-P-K numbers as a synthetic fertilizer, but after each N-P-K number, the percentage that comes from natural or synthetic sources will be noted in parentheses.
Whatever liquid fertilizer you choose, make sure it fits the plant you want to feed. When in doubt, research your plant online and choose a plant food formulated for its specific needs.