To optimize performance, improve plant appearance, and ensure longevity there are a few maintenance activities that gardeners should consider. Most perennials can be grown successfully with relatively little maintenance, while other perennials will require more work to keep them in good condition.
Although most perennials are not considered to be ‘heavy feeders’, it is important that they are produced with an adequate nutrient supply. Mulching the perennial beds with compost each year often supplies an ample supply of nutrients. In beds covered with bark mulches, it is recommended to fertilize once or twice per year with a general purpose fertilizer. Applying too much fertilizer causes many perennials to grow too quickly and become floppy. Do not apply fertilizer directly on top of the crown or severe injury from the salts may result. Perennials with tall flower spikes or full heavy flowers, such as Alcea or Delphinium, may require staking to prevent them from toppling over following heavy rains and high winds.
Several perennials benefit from deadheading, thinning, or cutting them back. Deadheading entails removing the dead flower heads and faded flowers; this practice keeps the garden looking nice and encourages many perennials to continue blooming for an extended period and improves the appearance of the plant. A few perennials benefit from thinning or removing some of the stems from the dense bushy clumps in the early spring which allows more air circulation and reduces the conditions for certain foliar diseases such as powdery mildew. Similar to deadheading, cutting some perennials back after they flower will often rejuvenate the clump by regenerating new growth and may possibly lead to another flush of flowers later in the growing season. Cutting back is also used to prevent some perennials from flopping over or to prevent the centers of the plants from opening up and appearing ragged following bloom.
Another important consideration is to prepare perennials for the winter. Do not fertilize perennials after they stop growing in the late summer or early fall. This will allow them to prepare for dormancy rather than encouraging them to remain actively growing. Many perennials go completely dormant (die back to the ground each year) and should have the foliage trimmed back before winter. Removing the existing foliage will make the perennial beds look cleaner and will decrease the likelihood of diseases setting in over the winter months or being carried over and infecting next years growth. Other perennials, such as ornamental grasses, are often trimmed in the spring allowing the foliage to provide some structure to the winter landscape. In northern zones or where tender perennials are being grown (marginal hardiness in your area) it is beneficial to apply mulch after the ground has frozen to help protect these perennials during harsh winters.