Pruning Perennials

Optimum health for your plants and a beautiful, well-maintained outdoor living area!

Why Prune?

Pruning is typically defined as removing growth from an herbaceous or woody plant to maintain the plant's health and vigor. The benefits of pruning include extending the blooming time, regenerating the plant, and encouraging new growth. Pruning regulates a plant's shape and size and also controls flowering and fruiting. It induces growth where and when it is wanted and can change the direction, quantity, and vigor of growth as desired. Pruning controls both the flower size and the number of flowers. When you prune your plant material, you allow for the optimum health of your plants but also for an ordered, well-maintained outdoor living area.

Tools Needed:

The tools needed for pruning your plant material include by-pass pruners, hand-held (or hedge) shears, loppers, and pruning saws. By-pass pruners are recommended for use in both deadheading and cutting back perennials because they make a clean cut through the stem of the plant. Hand-held, or hedge, shears are useful for pruning several stems at one time. They are a great pruning tool to use for cutting back plant material in the spring and the fall. Loppers are an efficient pruning tool for branches or thick stems that measure 1/2" to 2" in diameter. These are necessary for pruning bushes such as dogwood and lilac. Pruning saws are most effective for those plants, namely shrubs and trees, that have branches or stems measuring 1" to 3" in diameter. They make an extremely sharp, precise cut which allows the shrub or tree to heal.

All of these pruning tools are available for purchase from Ziegler's Landscape By Design .

Types of Pruning

The four basic types of pruning include deadheading, cutting back, pinching, and thinning.

Deadheading:

Deadheading perennials refers to the removal of spent flowers. When the spent flowers are left on the plant, they will eventually go to seed; and it is this production of seeds that consumes a great deal of the plant's energy. The plant's energy focuses on producing vegetative and root growth if it is not being used to produce seeds. Removing the spent, or old flowers is beneficial for the plant because it promotes the growth of new flowers.

Methods of deadheading differ depending on species and the growth habit of the plant. Most perennials should be pruned to the bud, lateral flower, or leaf. Pruning in this manner masks the cut that you have made and does not mar the attractiveness of the plant. Remember to look for new buds and flowers and to remove only the spent flowers from the plant. Perennials such as daylilies (Hermerocallis), have unattractive spent flowers and require frequent deadheading for aesthetic purposes. Other plants, such as hydrangea and false indigo (Baptisia australis), should be left unpruned because they offer beautiful seed heads. Certain plants need to be deadheaded to the ground or basal foliage, such as Heuchera and Alchemilla. If you are unsure which method of deadheading to use on which plant material, just consult your landscape designer.



Some plants need to be deadheaded to the ground or basal foliage such as Heuchera and Alchemilla. Most perennials should be pruned to the bud, lateral flower or leaf. When deadheading, prune off the spent flower stem to a new lateral flower or to a lateral bud. Pruning in this manner masks the cut that you have made and does not mar the attractiveness of the plant.

To promote self-seeding, it is best not to deadhead certain plant material. Columbine (Aquilegia) self-seeds in the garden and look very beautiful coming up in unexpected places. Hydrangea flowers look beautiful as they age and die. Yarrow (Achillea millefolium), bishop's goutweed (Aegopodium podagraria 'Variegatum'), bugleweed (Ajuga reptans), lady's mantle (Alchemilla mollis), columbine (Aquilegia hybrids), aster (Aster novi-belgii), maiden pink (Deanthus deltoides), purple coneflower (Echinacea purpurea), bloodred geranium (Geranium sanguineum), dame's rocket (Hesperis matronalis), wild sweet william (Phlox divaricata), orange coneflower (Rudbeckia fulgida 'Goldsturm'), and sweet violet (Viola odorata) make up some of the more common plants that self-seed. If necessary, deadheading becomes a useful method of keeping these plants confined to their designated space.

You may have selected plants to attract wildlife or birds in your outdoor living area. The seeds of many plants provide a great food source. These plants should be left unpruned so they go to seed. Purple coneflower (Echinacea purpurea), joe-pye weed (Eupatorium maculatum), sunflower (Helianthus salicifolius), spike gayfeather (Liatris spicata), beebalm (Monarda didyma), black-eyed susan (Rudbeckia hirta), and hosta offer attractive seed-heads that also are a good food source for birds.

Cutting Back:

Cutting back refers to pruning a plant to renew its appearance and to encourage new growth and flowering. Cutting a plant back to the ground is beneficial for certain spring-blooming species (see "Pruning Spring Flowering Perennials). Other perennials require cutting back later in the growing season.

Cutting back perennials controls the flowering time and the height of the plant. It can be done either before or after flowering. Cutting back is generally performed during the spring after growth has started. In an effort to cause the least amount of stress to the plant material, cut back early in the season when the weather is cool. In this type of pruning, remove all buds, flowers, and leaves with a hedge shears. As a general rule, plants that are cut back after they have flowered have regrowth that remains shorter than the normal mature height of the plant. Perennials should be pruned after flowering for maintenance or aesthetic reasons.

It may be necessary to cut some plants all the way down to the ground. Because new buds may be present slightly above the ground, allow approximately 2 inches of stem to remain. Special care needs to be taken with plants that are cut back to the ground. They should be well watered and the soil around the plant should be aerated.

Pinching:

Pinching improves the growth habit of the plant and also allows you to stagger bloom time. Only a small amount of the plant is removed in this type of pruning. Using your fingers, pinch the stem just aboce a node and only remove the growing tips and first set of leaves. Pinching is normally done in May or early-to-mid-June in the Midwest. Common yarrow (Achillea millefolium), Artemisia sp., Aster sp., pink turtlehead (Chelone iyonii), joe-pye weed (Eupatorium maculatum 'Gateway'), willowleaf sunflower (Helianthus salicifolius), cardinal flower (Lobelia cardinalis), beebalm (Monarda didyma), beardtongue (Penstemon barbatus), russian sage (Perovskia atriplicifolia), garden phlox (Phlox paniculata), Rudbeckia sp., Sedum 'Autumn Joy', goldenrod (Solidago hybrids), and spike speedwell (Veronica spicata) respond positively to pinching.

Thinning:

Thinning perennials improves their appearance, increases flower size, and prevents disease. Thinning refers to the removal of stems from a plant. To thin a plant, cut the stems to the ground in the spring. A general rule of thumb is to cut one in three stems. Plants prone to mildew, such as aster, delphinium, monarda, and phlox, respond favorably to thinning. The following perennials are also prone to rot or mildew and thinning improves the air circulation around these plants: Lady's mantle (Alchemilla mollis), bugleweed (Ajuga reptans), Bethlehem sage (Pulmonaria saccharata), beebalm (Monarda didyma), garden phlox (Phlox paniculata), and lamb's ear (Stachys byzantina).

Pruning Spring-Flowering Perennials

Many of the low-growing rock garden and edging plants benefit from being cut back to one-half the size of the plant after flowering. Pruning back by one-half the size of the plant prevents the plant from opening up at the center. This type of pruning is done mainly for aesthetic purposes. Rock garden plants that benefit from this type of pruning are: evergreen candytuft (Iberis sempervirens), maiden pink (Dianthus deltoides), and moss phlox (Phlox subulata). Some plants, such as catmint (Nepeta) rebloom after the pruning.

Many spring-flowering perennials can be cut back (as much as 1/2 the size) so that the garden remains well kept and green. The cutting of the plants promotes fresh, new growth that makes the plant look more attractive. The following is a short list of spring-blooming perennials that benefit from this type of pruning: Columbine (Aquilegia hybrids), rock cress (Arabis caucasica), siberian bugloss (Brunnera macrophylla), ground clematis (Clematis recta), maiden pink (Dianthus deltoides), dame's rocket (Hesperis matronalis), evergreen candytuft (Iberis sempervirens), bearded iris (Iris hybrids), spotted deadnettle (Lamium maculatum), catmint (Nepeta mussinii), wild sweet william (Phlox divaricata), moss phlox (Phlox subulata), and wooly thyme (Thymus praecox).

Pruning Summer-Flowering Perennials

The main difference between pruning spring-or- summer-flowering perennials is the amount of cutting back that is required after flowering. Some perennials should be pruned before flowering and others should be pruned after flowering. Pruning after flowering improves the aesthetics of the garden. Certain plants look best if they are cut back by 0ne-half or one-third of their mature height. Cutting out the brown parts of the plant stimulates growth of fresh green foliage. The following os a list of perennials that benefit from cutting back in the summer: Bishop's goutweed (Aegopodium podagraria 'Variegatum'), lady's mantle (Alchemilla mollis), southernwood (Artemisia abrotanum), wormwood (Artemisia schmidtiana 'Nana'), false indigo (Baptisia australis), tickseed (Coreopsis grandiflora), foxglove (Digitalis purpurea), queen-of -the-prairie (Filipendula rubra 'Venusta'), Geum hybrids, sunflower heliopsis (Heliopsis helianthoides), daylily (Hemerocallis sp.), small-flowered alumroot (Heuchera micrantha 'Palace Purple'), wild sweet william (Phlox maculata), garden phlox (Phlox paniculata), goldenrod (Solidago hybrids), and virginia spiderwort (Tradescantia x andersoniana).

Some perennials can be cut back before flowering for height control and to stagger or delay bloom time. Staggering the bloom time may lengthen the bloom time of the plant and it is also a great way to control when a plant will bloom.