2. Baby the roots. The delicate tips of a plants roots are the primary place where it takes up water and nutrients. Be careful not to damage the tips by cutting or tearing the root mass when planting. If you damage them, the plant will take longer to get established and start blooming until new ones can form. One exception: If you lift a perennial plant from a pot and see that the primary roots are wrapping around themselves in the pot, you should carefully straighten the circling roots and cut them so that they will grow into the surrounding soil.
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."