Spring Garden’s Corner

April 7, 2020

Written by Eric Kimbrel, Director of Horticulture

Winter is gone now but winter weeds persist! I see chickweed species and bittercress creeping up in the landscape and quickly trying to flower. These weeds should be pulled as soon as possible, because once they begin producing seeds, they become more difficult to control. One organic method of weed control we use to help prevent against this spread is corn gluten. Corn gluten is a powdery byproduct of the corn milling process and contains about nine percent nitrogen. Corn gluten does not prevent weed seed from germinating, but instead inhibits seeds from forming roots after germination. This means that corn gluten must be timed to be applied before the weed has established, otherwise the corn gluten will serve only to fertilize the weeds. Corn gluten needs water just after application, but a dry period following is required in order to inhibit root production for those germinated weed seeds. It can be quite difficult to get this application timing precisely correct but it can be up to 80% effective if applied right.  Timing is important in gardening and horticultural tasks.  Depending on the weather, we adjust our horticultural tasks each week at the Reserve to ensure our work in the gardens has the best impact.

After winter cleanup of branches and limbs on the forest floor and arborist visits, we have plenty of wood chips to put back in the garden. Wood chips contain both nutrients and food for microbes, fungi, bacteria and other soil-borne organisms that are so beneficial to soil health.  We use them to line trails as well as to capture and slow water.  Returning the wood to the forest floor continues the natural cycle that helps generate the soil.

The health of our soils is so important to creating a vigorous and productive garden during the remainder of the year. As spring approaches, amendments such as fertilizers, manure, compost, and lime (just to name a few), may need to be added to keep soil chemistry in check.  One way we determine which amendments to use is to conduct a soil test. Soil testing can be done by the North Carolina Department of Agriculture and Consumer Services for free from April through November and for $4 from November through March. Take advantage of this great resource!

One of the most important characteristics to pay attention to is the pH of the soil. Remember that scale of 1 to 14, acidic to basic, battery acid to bleach? A pH between 6 and 7.5 is optimum for plant nutrient uptake. We aim for 6.50-6.80 at the Reserve, knowing our native soils can be as low as 4. Your region’s geology is a large part what determines your soil pH, so find out a little more about your area’s geologic history. Nitrogen fertilizer can also cause your pH to become more acidic, or drop, so if you fertilize regularly you may need to occasionally offset this decrease in pH. To increase the pH of soils, we like to use Pennington fast acting lime because it is five times stronger and begins working immediately. Best of all though you can use less of it, saving materials and labor. Other limes help to reduce the pH of soils as well; white lime takes one year to be broken down and used by the plant, while pelletized, dolomitic or burnt lime, which is grey in color, begins working immediately. Lime may be applied any time of year. While not as common, if you need to decrease the pH of your soil (perhaps for specific plants, such as azaleas or blueberries), we recommend powdered elemental sulfur, sometimes called flowers of sulfur, to make soil pH more acidic. To be effective, sulfur needs to be spread evenly, perhaps in several applications, and given several months to interact with the soil.

In early spring, we are focused on cleaning up our garden beds as plants are emerging from the winter dormancy.  Recently we cut down all perennials in our Wildflower Labyrinth and conducted our annual controlled burn on grasses.  We left the stalks of perennials up during winter as a habitat for native insects to overwinter.  In other garden rooms we are removing leaves and weeds to make room for more plantings and mulch.

We encourage you to explore the new “Ask a Horticulturist” section of our website, a free resource where we will attempt to answer your gardening and native plant questions.