Fertilizing the Summer Vegetable Garden
One of the most common questions that we get this time of year is how to fertilize vegetable gardens. That’s understandable, since there are so many products available, each promising lush growth. It’s sometimes difficult to wade through the hype and choose the right product.
So how do you know what your soil needs? A soil test will tell you how much lime and nutrients to add. Keep in mind that if your pH level is too low or too high, the fertilizer you put out won’t be taken up by the plants. Soil tests are free to North Carolina residents, and kits can be picked up at your local Extension office.
Plants require several nutrients, but the ones they need in the greatest quantities are nitrogen, phosphorus, and potassium. These nutrients correlate with the three numbers on a package of fertilizer. For example, 10-10-10 fertilizer contains 10% nitrogen, 10% phosphorus, and 10% potassium.
Often the nutrient that is most limiting in our soils is nitrogen. Nitrogen deficiency will usually show up in a plant as a yellowing of the lower leaves. We saw a lot of nitrogen deficiency last year, because the frequent rainfall was washing the fertilizer away from plants.
Fertilizers can be either synthetic or organic, based on their source of nutrients. Synthetic fertilizers include the traditional 10-10-10 and similar products.
Organic fertilizers are derived from natural substances and include fish emulsion and cottonseed meal. These products tend to have a lower concentration of nutrients than synthetic fertilizers. There are many different types of organic fertilizers available at garden centers.
Synthetic fertilizers tend to release nutrients quickly, so the nutrients are readily available to plants. Organic fertilizers, on the other hand, release the nutrients slowly, over a longer period of time.
There are also some synthetic slow-release fertilizers (also called controlled release fertilizers). These products contain nutrients coated with a covering that dissolves when soil moisture and temperature are adequate. These products release nutrients at about the same rate as organic fertilizers do.
When we talk about organic fertilizers, some people may think of compost. Compost is great for soil, because it improves the soil’s capacity to hold nutrients, but it is generally low in nutrients.
Generally, it is best to broadcast half of the recommended fertilizer over the garden and till it in prior to planting. Then follow up by banding fertilizer in furrows next to the row or side-dressing vegetables as they grow. Keep fertilizer a few inches from the base of the plant to avoid salt injury.
If you have questions about your garden or landscape, contact the Caldwell County Cooperative Extension Service at 828-757-1290.