At Frank's Nursery in Columbia, the tardy arrival of spring has made for extra work to ensure the plants stay healthy as they wait for new owners. The cold is a factor, notes Frank Rhodes Jr., but the wind is especially dangerous to young plants. As a result, plants are staying in the greenhouses longer than normal this year. But Mother's Day, which is on May 13, and customers' spring gardening plans won't wait. So the flowering plants have to be ready. Temperatures are expected to be more seasonable this week.