An important aspect of pruning is knowing when to prune plants. Proper timing helps to insure attractive, healthy, productive plants. The proper time to prune trees, shrubs, and vines in Iowa is indicated below.
February through March is generally regarded as the best time to prune most deciduous trees. The absence of foliage at this time of year gives the individual a clear view of the tree and allows the selection and removal of appropriate branches. Also, when pruned in late winter, the walling-off or compartmentalization of wounds can begin immediately with the onset of growth in spring. Oaks are an exception. The winter months – December, January, and February – are the best time to prune oak trees.
Deciduous trees can be pruned at other times of the year with little or no negative consequences (To clean up storm damage, for example). However, if possible, avoid pruning deciduous trees in spring when the trees are leafing out and in fall when the trees are dropping their leaves.
The Best Time to Prune Oaks
To reduce the risk of an oak wilt infection, do not prune oaks from March through October. Oak wilt is a fungal disease that is lethal to many oaks. It can spread from infected trees to healthy trees by sap-feeding beetles ("picnic bugs"). If an oak tree must be pruned in spring or summer (such as after a storm), apply latex house paint to the pruning cuts to avoid attracting sap-feeding beetles to the wounds. Learn more about Oak Wilt in these articles: Pruning Oak Trees to Avoid Oak Wilt and Oak Wilt.
FAQs - Deciduous Trees
- When is the best time to prune shade trees? | Short answer: February and March
- When is the best time to prune oak trees? | Short answer: December through February
Evergreen trees, such as pine, spruce, and fir, require little pruning. Dead, broken, and diseased branches can be removed at any time of the year. Late winter is the best time to remove unwanted lower branches on evergreen trees.
Spruce and fir trees possess side or lateral buds on their newest (outermost) growth. To promote denser growth, cut shoots back to just above a lateral bud or side branch in early spring.
Growth on pine trees develops from terminal buds. Pines do not produce side or lateral buds. The growth of pines can be slowed by pinching or pruning off one-half to two-thirds of the elongated terminal buds ("candles") in spring when the candles are approximately 2 to 3 inches long. Do not prune branches back to older growth down the stem as new growth will not develop from these areas.
The proper time to prune deciduous shrubs is determined by the plant's growth habit, bloom time, and health or condition.
Spring-flowering shrubs, such as lilac and forsythia, bloom in spring on the growth of the previous season. The plant's health or condition determines the best time to prune spring-flowering shrubs.
The best time to prune healthy, well-maintained spring-flowering shrubs is immediately after flowering. Healthy, well-maintained shrubs should require only light to moderate pruning. Pruning immediately after flowering allows gardeners to enjoy the spring flower display and provides adequate time for the shrubs to initiate new flower buds for next season.
Summer-flowering shrubs, such as potentilla and Japanese spirea, bloom in summer on the current year's growth. Prune summer-flowering shrubs in late winter or early spring. The pruned shrubs will bloom in summer on the current season's growth.
Shrubs with Non-Showy Flowers
Some deciduous shrubs don't produce attractive flowers, such as burning bush. These shrubs may possess colorful bark, fruit, or foliage. Prune these shrubs in late winter or early spring before growth begins.
Neglected, overgrown shrubs often require extensive pruning to rejuvenate or renew the plants. The best time to rejuvenate large, overgrown shrubs is late winter or early spring (March or early April). Heavy pruning in late winter or early spring will reduce or eliminate the flower display on spring-flowering shrubs for 2 or 3 years. However, rejuvenation pruning will restore the health of the shrubs. More information can be found in this article: Pruning Large, Overgrown Shrubs
Formal Deciduous Shrub Hedges
Most deciduous shrubs should not be sheared into formal hedges. It destroys their natural shape, reduces the number of leaves and flowers within the shrub's canopy, and causes a proliferation of small shoots at the branch tips that will look unsightly.
A few species, namely privet, alpine currant, and barberry, can be successfully managed as formal, sheared hedges. To maintain a formal shape, pruning is required at least twice a year. Begin shearing deciduous hedges in spring just after the new flush of growth appears (May). A second shearing can be done in mid-summer (July) if needed. Avoid extensive pruning after mid-summer as it will promote new growth that cannot harden off well before winter arrives. More information can be found in this article: How to Prune Formal Hedges
Don't Prune in Late Summer and Fall
Do not prune deciduous shrubs in late summer. Pruning shrubs in August or early September may encourage a late flush of growth. This new growth may not harden sufficiently before the arrival of cold weather and be susceptible to winter injury.
FAQs - Pruning Shrubs
- When should I prune spring-flowering deciduous shrubs? | Short answer: Immediately after flowering
- When is the best time to prune forsythias? | Short answer: Immediately after flowering
- When should I prune my weigela? | Short answer: Lightly in early spring and again (if needed) after bloom
- When should I prune summer-flowering deciduous shrubs? | Short answer: March and early April
- When would be the best time to prune potentillas? | Short answer: March and early April
- When should I prune “non-flowering” deciduous shrubs? | Short answer: February and March
Prune evergreen shrubs, such as juniper and yew, in late March or early April before new growth begins. Light pruning may also be done in mid-summer. Avoid pruning evergreen shrubs in the fall. Fall-pruned evergreens are more susceptible to winter injury.
Formal Evergreen Hedges
To maintain a formal shape, pruning is required at least twice a year - the tidiest of hedges require pruning almost monthly. Begin shearing evergreen hedges in late spring or early summer just after the new flush of growth appears (May through early June). Avoid extensive pruning after mid-summer.
Boxwoods often experience dieback in severe winters. Prune out dead growth in early spring (early to mid-April). Light pruning/shearing (to shape plants) can be done from spring to mid-summer. Do not prune boxwoods in late summer as late-season growth may not have sufficient time to harden before winter. More information can be found in this article: How to Prune Formal Hedges
FAQs - Pruning Evergreen Shrubs
- When should I prune evergreen shrubs? | Short answer: Early Spring and (if needed) mid-summer
Late February to early April is the best time to prune fruit trees in Iowa. Pruning should be completed before the fruit trees begin to break bud (leaf out) in early spring.
Early spring is also the best time to prune most small fruits with woody stems such as grapes, raspberries, blueberries, gooseberries, and currents.
FAQs - Pruning Fruit
- When should I prune my fruit trees? | Short answer: Late February through early April
- When is the best time to prune grapevines? | Short answer: Late February through early April
The upper portions of modern roses, such as hybrid teas, floribundas, and grandifloras, typically have winter dieback due to exposure to low winter temperatures and extreme temperature changes. Gardeners should prune out the dead wood after the winter protection is removed from modern roses in late March to mid-April.
Old garden roses, hybrid rugosas, and other hardy shrub or landscape roses often survive Iowa's winters with little or no winter injury. Those that bloom only once a year should be pruned immediately after flowering. Those that bloom throughout the summer should be pruned in March or early April.
More information can be found in this article: How to Prune Roses.
Most vines can be pruned in late winter or early spring before they begin to leaf out (March through early April). The exception to this are spring flowering vines, such as wistera, which should be pruned immediately after flowering.
Clematis varieties can be placed into three groups based on their flowering characteristics.
- Bloom on the current season’s growth. These varieties tend to produce one flush of blooms sometime between late May and September. They are some of the most common types found in Iowa. (Examples: Clematis viticella, Clematis terniflora, and large-flowered hybrids such as Clematis × jackmanii, ‘Ernest Markham’, and ‘Hagley Hybrid’)
- Bloom on the previous year’s growth referred to as old wood. These varieties are the earliest to bloom in Iowa often flowering in May. (Examples: Clematis alpina and Clematis macropetala)
- Bloom on both old and new wood. These varieties bloom twice each season. Large flowers appear between May and July and a second flush of smaller flowers happens in late summer. (Examples: ‘The President', ‘Henryi’, and ‘Ramona’)
Prune clematis vines that bloom on the current season's growth back to within 6 to 12 inches of the ground in late winter/early spring (Mid-March to Mid-April).
Wait until the vines begin to leaf out before pruning the other two groups of clematis. Prune out all the dead wood once the vines begin to leaf out. Clematis vines of the last 2 groups will bloom poorly if much of the old growth is destroyed in winter.