Fertilizing is important for keeping plants healthy | Hometown focus
As gardeners, we want to keep our plants healthy and productive. Unfortunately, most garden soils do not provide enough nutrients for our plants to thrive. It’s up to us to help.
Adding compost and other organic materials improves the health and fertility of our soil, but our plants need readily available nutrients to grow strong. Below are the key nutrients that plants need.
Nitrogen promotes new growth. It is a water-soluble nutrient that is washed away by rain or consumed by the plant.
Phosphorus stimulates root growth and helps plants move nutrients between the roots and the leaves and flowers. Phosphorus may be present in the soil but not available to the plant due to pH, microbes, or soil temperature.
Potassium helps plants move water, nutrients, and carbohydrates from one area to another. It is also responsible for stimulating early growth, improving resilience and increasing resistance to insect pests and diseases. Most fertilizers contain the three most important plant nutrients.
Nitrogen (N), phosphorus (P) and potassium (K) and secondary nutrients magnesium, calcium, sulfur, iron and boron. The NPK ratio on the fertilizer package indicates the percentage by weight of each nutrient.
Organic fertilizers are made from naturally occurring mineral deposits and organic components such as bone meal or manure. Over time, they contribute to soil texture and fertility and add important secondary nutrients and trace elements. Most organic fertilizers are insoluble in water, so their nutrients are slowly available to the plants over a period of months or years. However, liquid fish and algae emulsions are exceptions and bring nutrients to the plants immediately.
Synthetic fertilizers often start organic but are treated chemically to make them water soluble and readily available to plants. They are valuable when plants are growing quickly and in need of nutrients. However, they do not improve soil life or soil fertility. They are available in slow release and water soluble forms.
The recommended application rate must not be exceeded with any fertilizer, especially with synthetic fertilizers.
Not all plants require the same amount of nutrients or need them at the same time during the season. Always follow the instructions on the pack as the application rates will vary depending on the nutrient content, whether the fertilizer is synthetic or organic, and whether it is granular, timed or water-soluble.
Trees and bushes: When planting, work fertilizer into the root zone to release the plant food slowly and evenly. Established trees and shrubs can be fertilized in early spring. If trees and shrubs are healthy and developing well, they may not need fertilization at all. There are special fertilizers for different types of trees and bushes.
Perennials: Mix in an organic all-purpose fertilizer when planting.
Bulbs: Spring-blooming bulbs such as tulips do not need fertilization. Onions grown as perennials such as daffodils can be fertilized before or after flowering. Summer blooming flowers like dahlias and lilies can be fertilized at planting time. Heavy fertilizers like dahlias can be fertilized monthly with a low-nitrogen fertilizer.
Annuals: Most annual flowers and vegetables are powerful feeders. Use an all-purpose granular fertilizer at planting time, then use a low-nitrogen liquid fertilizer once or twice a month. If it’s extremely hot, which we had this summer, cut down on the extra fertilizer until it cools down.
Container plants: Most container plants need more fertilizer than your garden plants. Potting soil contains fewer nutrients, and watering washes the nutrients out of the soil before they can be absorbed by the plants. Flowering annual plants need a good supply of nutrients in order to bloom continuously. For best results, apply a water-soluble half strength fertilizer during the growing season or every 6 to 8 weeks, apply a time-release fertilizer. While you want your plants to be healthy, applying too much fertilizer can be harmful.
Too much nitrogen produces a lot of leaves and fewer flowers and fruits. Too much phosphorus makes it difficult for plants to absorb iron and zinc. Too much potassium prevents them from absorbing calcium. Excess fertilizer can find its way into groundwater and bodies of water, damage ecosystems and pollute drinking water.
Always follow the package directions for application rates and timing. When in doubt, be conservative. Get to know your plants too. Many plants, such as lavender, do not need additional fertilizer. Have fun gardening!
Donna Tini is a master gardener who lives on Long Lake near Eveleth. She is retired but retains the title of professional grandmother. She enjoys her book club, does handicrafts, bakes and of course in the garden in the change of seasons. She is a new home and garden columnist whose column is currently scheduled to appear on the third Friday of each month.