Pruning Rules of Thumb

Why prune?

  • Form
  • Size control
  • Health
  • Rehabilitation

Pruning Evergreens

  • Arborvitae, Juniper and Chamaecyparis should be pruned when pushing new growth in late spring or early summer. These types of evergreens won’t form new buds on old wood so don’t prune back to the older brown, aged stems. Snip branch tips back lightly.
  • Hemlocks and Yews should be pruned when dormant in late winter or late summer. They can be trained into formal hedges or to encourage fullness. After pruning they will get a new flush of growth.
  • Pines can be pruned when pushing new growth in spring. Current years new shoots (“candles”) can be cut or pinched off. If you prune during the push of new growth new shoots will have time to develop for next year’s growth.
  • Firs and Spruces can be pruned when dormant in late winter or late summer. Trim the outermost branch tips to encourage fullness. Also trim the leader to control height and encourage outward growth. Cut ½ inch or so above a bud.

Pruning Deciduous shrubs

  • Remove dead or damaged branches.
  • Prune spring-flowering shrubs AFTER they’ve finished blooming.
  • Privet, Dwarf Spireas and Red Twig Dogwoods can be cut back heavily to stimulate fresh new stems.

Pruning Shrub Roses

  • Remove stems that have died back through the winter.
  • Remove any damaged canes, or any weak stems.
  • Unless you are pruning to control size the roses should not be pruned back further. During the flowering season you may want to dead-head your roses (cut dead flowers off back to just above healthy leaf set) to improve appearance and promote more flowering.

Pruning Hydrangeas

With Hydrangeas, NO pruning is better than incorrect pruning. In fact, most varieties will grow and flower to some degree if they are never pruned at all, provided that they are properly cared for and planted in a protected location (if required). When and how you prune your Hydrangea depends on the type of Hydrangea, and if flowers are produced on old or new growth. “Old Wood” are stems that have been on the hydrangea since the summer before the current season. “New wood” are stems that developed on the plant during the current season.

Annabelle (arborescens) and Pee Gee (Paniculata) flower on new growth. This includes Limelight, Quickfire, Pinky Winky, and Little Lamb types. No pruning is really necessary except to remove spent flowers, broken or entangled branches and for general shaping. The best time to prune is in early spring before growth begins, or late fall and winter. Annabelle Hydrangeas may be treated like woody perennials and cut down to 3” each spring to encourage compact growth habit. They will still bloom beautifully in the spring/summer, however this drastic pruning may not allow stems to increase in size, and they may need staking to hold up the large heads.

Endless Summer series flowers on old growth and new growth. Prune dead stem growth after buds emerge in the spring. Don’t treat your Endless Summer Hydrangeas like an Annabelle Hydrangea by cutting them back in the fall or early spring. By cutting to the ground or within a few inches of the ground, most if not all of the buds on old wood are being removed. In addition, the old blooms of Endless Summer add to the winter interest of your garden. Endless Summer Hydrangeas certainly do bloom on new wood, but it may take longer for flower buds to develop on the new growth of a young plant.

Oakleaf types flower on old growth. Delay spring pruning until growth has fully emerged. At this time, remove any winter damaged tips or stems that have not produced leaves. Once established (3 +years), Oakleaf Hydrangeas suffer little dieback if they are planted in a winter protected area, unless the previous winter has been extremely cold with sustained temperatures below — 10 F. Heavy pruning should occur immediately after flowering, while removal of an occasional branch or two for shaping purposes can be done at any time during the growing season.

Big Leaf and Serrata types flower on old growth. This group of hydrangeas produces flower buds on stems around August, September or October for the following summer’s blooms. Delay spring pruning until growth has fully emerged. At this time, remove any winter damaged tips or stems that have not produced leaves. Flower buds form near the stem tips during the previous year and may be accidentally removed if pruned back too far, and you may have a beautiful plant with no flowers because of winter die-back or incorrect pruning. Additional selective pruning may be done in late summer to remove the spent blossoms if desired.

There are certain instances when pruning Hydrangeas can be helpful:

  1. All dead stems should be removed from hydrangeas every year.
  2. After the plants are at least 5 years old, about 1/3 of the older (living) stems can be removed down to the ground each summer. This will revitalize the plant.
  3. In addition, if it becomes necessary to prune a plant to reduce its size, it may be cut back in June or July without harming the next year’s bloom. But it will return almost immediately to its former size. This is one reason why it’s best to plant a hydrangea where it does not have to be pruned.

Beware the Urge to Prune Everything in the Fall

Educate yourself about the plants that you have, and how they react to pruning. Find out when your plants bloom, and plan pruning according to that schedule. Spring-flowering shrubs and trees will have already set buds for the next year. Pruning in the fall removes the flowers that you’ve worked so hard to preserve.

Avoid pruning:

  • Lilac
  • Viburnum
  • Smokebush
  • Fothergilla
  • Forsythia
  • Magnolia
  • Ninebark
  • Spiraea
  • Weigela

Perennials may be left to stand and provide winter interest, or maybe cut back to the ground. It’s a matter of personal preference. Some perennials provide food for birds and other wildlife through the winter if left standing.

Grasses should be left standing until spring. We’ve found that grasses survive better if left until early spring. At that point cut grasses back to several inches tall before they begin to show new growth.

If you’re not sure please contact us at the nursery (Phone: 260-637-5816) or contact the Allen County Purdue Extension Office (Phone: 260-481-6826)

Sources: Maintenance PruningHow to Prune Conifers (April 2009), Maintenance Pruning

Beware the Urge to Prune Everything in the Fall