3. Plant high. Set perennials with their crowns (the place where the plants' shoots meet the roots) slightly above the soil surface, say researchers at Cornell University's Flower Bulb Research Program. This produces stronger growth than the widespread practice of planting the crown 1 to 2 inches below the soil surface.
4. Feed for flowers. If a soil test shows that your soil needs more nutrients than compost can supply, apply a slow-release organic fertilizer. Scientists at the University of Assiut in Egypt found that New York asters (Aster novi-belgii) given slow-release fertilizer bore more flowers, developed more branches, and produced more chlorophyll. Look for granular organic fertilizers in nurseries, home centers, and mail-order catalogs.
5. Mulch matters. Shrubs growing in soil that has been mulched are larger, more vigorous, and more likely to survive their first year than unmulched plants, report researchers at Washington State University. Key to the mulched plots' success was improved water retention in the soil and less competition from weeds. The study was discontinued early, says the lead researcher Linda Chalker-Scott, Ph.D., because "all the plants in the unmulched sites died."