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Get the most out of your fertilizer

  • Nanette Londeree
  • Many fruits and vegetables use up nutrients in the soil rapidly and need to have them replenished during the growing season.  Photo: PxHere
    Many fruits and vegetables use up nutrients in the soil rapidly and need to have them replenished during the growing season. Photo: PxHere
    We gardeners are an enthusiastic bunch who want to give our plants all they need to flourish. This includes the right location, healthy soil, and water, as well as a balanced diet. It takes a lot of energy for a plant to produce flowers, fruit, and seeds while developing healthy roots and leaves for photosynthesis. Plants pull out nutrients as they grow, and fertilizing replenishes them.

    Plants get their nutrients from the organic matter and minerals found in the soil or from added fertilizers and compost. With the best of intentions, we routinely fertilize, whether the plant needs it or not. Rather than spend money on something that may not be necessary, here are some Earth-friendly ways you can get the most out of your fertilizer:

    Know what your plant needs: Different types of plants have varying nutrient needs, and the soil's ability to supply those nutrients can vary by location, season, and weather conditions. Many woody ornamentals such as nonflowering trees and shrubs, along with native plants, don't require fertilizer, even at planting. Fruit trees, vegetables, and flowering annual plants have variable fertilizer requirements. 

    Add only what's needed: Most of the 18 chemical elements plants need for growth are already in the soil or the air and don't need to be added regularly. Test your soil for the big three—nitrogen, phosphorus, and potassium (N-P-K)—and then add only the nutrients the soil test results indicate are lacking. 

    In addition to small amounts of nitrogen, phosphorus, and potassium, compost supplies micronutrients and organic matter to the soil. Photo: Pexels
    In addition to small amounts of nitrogen, phosphorus, and potassium, compost supplies micronutrients and organic matter to the soil. Photo: Pexels
    Pay attention to soil pH (acidity/alkalinity): When pH is too low or too high, chemical reactions can alter soil nutrient availability and biological activity. Most garden plants grow best in a soil pH range of 6.0 to 7.0.   

    Use it at the right time of year: Fertilizing too early or late in the season can be a waste of material and money. Nutrients may be leached out of the soil if applied before seasonal rains end. Fertilizing in late summer and early fall can encourage tender late growth that is easily killed in winter.

    Opt for natural fertilizers: Many organic materials (carbon-based and derived from living organisms) contain not only N, P, and K but also other essential plant nutrients. They also provide carbon to feed soil microorganisms, increase soil organic matter, and improve overall soil health. Often sold as meals, these materials release nutrients slowly over a longer period, allowing plants to absorb them more efficiently. 

    Know what you're using: It's easy to be swayed by costly specialized products for different plant types – one for azaleas, roses, citrus, etc. Often, these products are simply N, P, and K in various concentrations. You can get the same nutrients in more affordable, generic products. Before buying, please read the product label and be sure it contains what you need.  

    More is not better: Too much fertilizer, whether applied too often, too much in a single application or added at the wrong time, can burn or desiccate roots. It can lead to weak, succulent growth, encourage insect pests and disease problems, and contribute to water pollution. 

    Soil pH above 7.0 can reduce iron availability to plants and result in chlorosis - pale leaves with green veins. Photo: Wikimedia Commons
    Soil pH above 7.0 can reduce iron availability to plants and result in chlorosis - pale leaves with green veins. Photo: Wikimedia Commons
    Take care with controlled-release products: Pellet-like granules of multi-element fertilizer are coated with a substance that slowly breaks down, allowing the release of a small, steady amount of nutrients over time. However, the types of coatings used vary and may include synthetic polymers that may persist in soils.   

    Avoid multipurpose products: These products contain a mixture of fertilizer, insecticide, and fungicide or fertilizer and herbicide (weed and feed lawn products). Using combination fertilizer products when no specific insect pest, disease, or weeds are present adds pesticides to the soil for no purpose. It can negatively impact soil organisms, bees, and other pollinators and is much more expensive than single-use products.   

    Not a cure-all: Fertilizers won't help plants injured by insect pests and diseases, location, or weather problems unless soil nutrients are deficient.  

    To learn more about fertilizing, visit our website at https://marinmg.ucanr.edu/.