Monday, April 9, 2012

Landscape Plants for N.C. Gardens: Spring

By Kate Blakely

As the last frost date approaches next week, our urge to plant is strong. But some plants fare far better in the Triangle than others, as gardeners often learn by trial and error.

If you’d like some guidance in selecting the best plants for this region and growing them successfully, we’ve got the perfect class for you. “Landscape Plants for North Carolina Gardens: Spring” begins this week and runs for four Thursdays from 10 a.m. to noon.

Robert Mottern, Duke Gardens’ director of horticulture, will teach the class. He shared a few tips to help get you started with soil preparation and plant placement.

The soil in the Triangle area is almost all clay. Clay-based soils can serve as rich ground for gardening, Mottern says, but it has to be loosened to facilitate strong root growth. You must also incorporate organic matter. That means amending the soil with composts, manures and sometimes sand.

Clay does a good job of holding nutrients and water. However, the soil structure of clay can make these nutrients and water unavailable to plants. Adding organic matter and some sand helps break up the clay, releasing vital nutrients and improving moisture availability that encourages root growth. Worms like a loose, moist soil as well, Mottern says. Their natural processes amend the soil as they assist in breaking down organic matter.

Mottern likes composted manures like Black Cow, and other organic sources of fertilizer. Composted products have much of their nutrient base already available for plants. You never want to add fresh kitchen waste or lawn clippings to your soil. Add these to your compost pile and make sure they are already broken down at least half-way before amending your soil with them.

Organic amendments are preferable to synthetic, Mottern says. They generally carry a low nutrient load and break down slowly in the soil, keeping plants and soil microbes in a state of harmony. Synthetic fertilizer can overload the soil with nutrients, thus encouraging rapid, unhealthy plant growth. If overused, these nutrients pollute stormwater runoff and contribute to algae blooms in our streams and wetlands.

Be mindful of temperature changes and your plants’ exposure. Freezing temperatures affect many plants, and low-lying areas tend to act as cold air sinks during the winter. A lower space can be 2 to 3 degrees cooler than surrounding higher ground. That makes a difference to many plants when the thermometer approaches freezing. Boulders, paving and building walls all help retain heat. Help protect cold-sensitive plants by planting them near these features. Orienting them facing south also helps, for maximum sun during the winter months.

If you’d like to learn more about planting, and about dozens of plant species that will fare well and look fantastic in your gardens, consider signing up for “Landscape Plants for North Carolina Gardens.” The class is limited to 15 students, so there is plenty of time for addressing gardeners’ questions and concerns. The fee is $105; $85 for Gardens members. Mottern’s summer plant class in this series (focusing on different plants) will run on Thursdays from May 31 to June 28, also from 10 a.m. to noon.

To register for this or other classes, or for more information, please call our registrar at 919-668-1707, or send an email. For more information about other classes and public events at Duke Gardens, please go to

Sarah P. Duke Gardens creates and nurtures an environment in the heart of Duke University for learning, inspiration and enjoyment through excellence in horticulture. The Gardens is at 420 Anderson St.

Columnist Kate Blakely is a graduate student at Duke Divinity School and a work-study assistant at Duke Gardens. This column first appeared in the Durham Herald-Sun.

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