For healthy growth, all plants require certain nutrients. Recall the three macronutrients they need: nitrogen (N), phosphorus (P), and potassium (K). Nitrogen is important for stem and leaf growth and for the photosynthesis process. Phosphorus promotes root growth and improves flowering and fruiting. Potassium contributes to root development, the overall growth of the plant, and to disease resistance. Other essential nutrients are equally important, but plants require them in much smaller amounts. Plants acquire most nutrients from the soil by absorbing them through their roots. It is important that students learn that nutrition is as vital to plants as it is to them. Refer to the following lists for more detailed information.
Plant Macronutrients
Plant Micronutrients
The nutrient most often lacking in our soil is nitrogen, which is essential for good plant growth. During the growing season, most plants will periodically need additional applications of fertilizer. For example, vegetables need an application of nitrogen every 4 to 6 weeks. As a general rule, fertilize annuals when they produce the most active vegetative growth. Fertilize perennials before new growth begins and fruit trees, including citrus, in spring and early summer. California natives and succulents usually do not need fertilizer.
Fertilizers can be organic or inorganic. They can be liquid, water soluble or granular. Any product sold as a fertilizer will have a nutrient analysis on the label with three numbers. The numbers represent what percentage of the three major nutrients – nitrogen (first number), phosphorus (second number), and potassium (third number) – the fertilizer contains. The product label should also tell you how much to use for different crops and areas. NOTE: Check with school administrators to see if there are any restrictions on the type of fertilizer your class may use in the garden.
Follow the warnings on fertilizer products and store them in a secure location. Fertilizers should be handled by adults or under close adult supervision. Make sure to apply only the needed amount. Fertilize the plants after they have been well watered to avoid burning the roots. Seedlings should not be fertilized until they have at least one set of “true” leaves.
Read the instructions carefully and mix according to directions. When it comes to fertilizing, less is better. You might think that if a small amount of fertilizer will help your plant grow, that a lot of fertilizer will result in an even better harvest. However, the phrase “the more the better” is not applicable to fertilization. Excessive nitrogen fertilizer can damage plants, may produce succulent growth that is more susceptible to damage by pests and diseases, and lead to runoff of the extra nutrients.