It’s gardening season, this spring even more than usual.
The pandemic has made many people think about starting their own vegetable garden. Gardening is part art, part science. And in the Sandhills in particular, the science part may be particularly challenging. There are some soils in the state where gardening means putting a few transplants in the ground and adding water. Not in our sandy soils. In order to have a successful, productive vegetable garden, there are many subtle and yet complex elements that need to be addressed.
Most people are aware that plants need to be fertilized in order to grow well. Bags of fertilizer are labeled with the percentage of nitrogen, phosphorus, and potash (also known as N-P-K) in the bag. So a bag of 10-10-10 is 10% nitrogen, 10% phosphorus, and 10% potash (or potassium). A bag labelled 8-0-24 is eight percent nitrogen, zero phosphorus, and 24% potash. You get the picture. NPK are considered macronutrients for plants, along with carbon, hydrogen, oxygen, sulfur, magnesium, and calcium. Carbon, hydrogen and oxygen are provided by the environment (air and water); magnesium and calcium are readily available as long as the soil is properly limed to the correct pH, as both are components of liming material (if dolomitic lime is used). Sulfur is usually available from the atmosphere, although since air pollution has been reduced over the years, sulfur deficiencies are more common than they once were.
What is often forgotten in fertility considerations are the micronutrients. Micronutrients include iron, boron, manganese, nickel, zinc, copper, chlorine and molybdenum. Micronutrients, as the name suggests, are needed only in very, very small amounts by the plant, compared to macronutrients. For example, research in plant dry matter has found manganese at a level 1000 times less than nitrogen. And the amount of manganese is still 1,000 times more than the uber micronutrient, molybdenum. However, though needed in minute amounts, they are still essential for plant health. One commonly deficient micronutrient in sandy soils is boron. This nutrient is essential for pollen germination, seed and cell wall formation. Without sufficient boron, pollination may be poor, fruit misshapened, and developing leaves malformed. Boron is pretty important to have if you’re trying to grow vegetables!
In general, micronutrients are supplied through the soil, and the parent material – rock – from which that soil is derived. Unfortunately, sandy soil is a very poor source of micronutrients. Other sources include organic matter and organic fertilizers, such as compost and animal manures. Not only is compost and animal manure a source of micronutrients, those materials provide attachment points for all nutrients which sand alone does not have (water is also held by organic matter much better than sand alone). Correct soil pH is also critical to create an environment conducive to nutrient availability. Our natural soil pH is around 4.5-4.8, and most vegetables need 6.0-6.4. At low soil pH, nutrients are often unavailable to the plant or lost through leaching, especially boron and molybdenum.
Micronutrients can be purchased like any fertilizer, and applied to soil or, with some formulations, as a spray for direct foliar application (this is frequently done with boron and even calcium, which is not a micronutrient, but frequently deficient in fruit). Because micronutrients are need in such small amounts, foliar sprays can be an effective way to get micronutrients into plants. If you’re planting a vegetable garden, don’t forget to consider your micronutrients!
NC Cooperative Extension is here to help you with your gardening questions, even during this time of COVID 19. Give us a call at 910-997-8255, or follow us on Facebook, and check out our website at richmond.ces.ncsu.edu.
Paige Burns Clark is the director of the Richmond County Cooperative Extension.