Crocus - Pruning

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JUNE PRUNING JOBS Alan Titchmarch on early summer pruning of trees, shrubs and climbers or July

Early summer is a time to relax and enjoy your garden, but there are still some early-flowering shrubs that will need pruning if they are to produce the best possible displays year after year. A few shrubs can also be trained into unusual and attractive standards at this time of the year. This week is not too late to complete the pruning jobs for May if you haven’t got round to them yet.

SHRUBS

Buddleja
Unlike the butterfly bush (Buddleja davidii), B. globosa and B. alternifolia flower on shoots produced during the previous year, so if you pruned them hard in spring you would loose all of this year’s flowers. For this reason they are best pruned after flowering in early summer. Remove any dead or damaged growth and shorten lop-sided or over-long shoots to balance the overall shape of the shrub. Old and neglected shrubs can be rejuvenated by cutting out one-in-three stems, starting with the oldest. Either cut them back to a sideshoot lower down or remove them completely. You will loose some flowering shoots for next year but the shrub will be the better for it in subsequent years.

You can also train B. alternifolia as an attractive and unusual weeping standard. Select the most vigorous stem and tie this to a vertical cane after planting. Cut back most of the other stems, so that about ¾ of the growth is removed. Each year, tie in the new growth of the main stem to the cane and thin out the oldest sideshoots. These will encourage the main stem to thicken and become self-supporting in time. When the main stem reaches the required height, pinch out the growing tip to encourage sideshoots to form. All sideshoots lower down the stem should be removed. The following year, pinch out the sideshoots that form the head of the standard so that they branch and become bushy. In subsequent years, prune the standard during June after flowering by removing dead or damaged stems as well as thinning out congested growth. Then cut back the weeping flowered stems to a sideshoot that hasn’t produced flowers or to a plump bud near the main framework of branches. In this way you will get a succession of flowering stems year after year.

Cornus (winter-flowering dogwood)
The winter-flowering dogwoods, Cornus mas and Cornus officinalis are also grown for their attractive foliage and colourful fruits. They require little or no pruning other than the removal of dead or damaged stems. The foliage displays of variegated forms can be improved by cutting back one-in-three stems, starting with the oldest. This will encourage vigorous new growth. Old and neglected plants can be rejuvenated in the same way. Cornus mas also lends itself to being trained as a standard (see Buddleja, above).

Deutzia
Maintain the flowering performance of deutzias by pruning each year immediately after flowering. After planting, lightly trim to encourage bushy growth. In subsequent years cut back flowered stems to a sideshoot that hasn’t produced flowers or to a plump bud. Congested plants can have one-in-three stems removed, starting with the oldest. Old and neglected plants can be rejuvenated in the
same way.

Elaeagnus (oleaster)
Deciduous Elaeagnus angustifolia and E. umbellata varieties require little routine pruning other than the removal of dead or damaged stems. Old and neglected plants can be rejuvenated by cutting back one-in-three stems, starting with the oldest. Hedges can also be given a light trim at this time of the year and again in September.

Hippophae
The problem when pruning hippophae is identifying the dead stems from the live. That’s why it’s a good idea to wait until this month when you can clearly tell the difference, but wear eye-protection and gloves to protect yourself from thorny stems. Although little or no routine pruning is necessary, if the shrub is well established and growing well, you may need to thin out overcrowded stems in the centre of the shrub. Hippophae is also prone to suckering, but unlike other suckering shrubs won’t throw up even more vigorous suckers if these are pruned off at ground level. Old and neglected plants can be rejuvenated by pruning to about 10cm (4in) during early spring. Alternatively, if you find this too drastic, cut back one-in-three stems to near ground level, starting with the oldest.

Rosmarinus (rosemary)
If left untrimmed for many years, rosemary will become bare and ugly at the base and produce fewer flowers. After the main period of flowering is over, remove any dead or damaged growth and shorten lop-sided or over-long shoots to balance the overall shape of the shrub - cutting back to a sideshoot lower down. However, rosemary is reluctant to produce new shoots from woody stems so avoid pruning back into old wood. Old and neglected shrubs that are well clothed in foliage near the base can have all stems cut back by about half to sideshoots lower down on each stem, otherwise they do not respond to severe pruning and so are best replaced.

Spiraea (bridal wreath)
Spiraea ‘Arguta’ and S. veitchii should be pruned immediately after flowering to maintain flowering performance. After planting, lightly trim to encourage bushy growth. In subsequent years cut back flowered stems to a sideshoot that hasn’t produced flowers or to a plump bud. Congested plants can have one-in-three stems removed, starting with the oldest. Old and neglected plants can be rejuvenated by cutting back to near ground level, but the flowering display will be reduced for a few years. Alternatively, cut back one-in-three stems each year for three years, starting with the oldest. Hedges can also be trimmed immediately after flowering.

Syringa (common lilac)
After planting, trim lightly to produce a balanced shape. Where practical, deadhead lilacs as the flowers fade, taking care not to remove the new shoots that lie just underneath that will carry the following year’s flowers. Use a pair of secateurs and make a clean cut right at the base of the faded flower spike. Remove suckers by cutting them off cleanly from the roots or main stem. Old and neglected plants can be renovated by cutting all stems to a stubby framework about 45cm (18in) from the ground, or if this is too drastic for you, remove one-in-three of the oldest stems each year for three years until the whole shrub has been rejuvenated. Syringa meyeri also lends itself to being trained as a standard (see Buddleja, above).

TREES

Grevillea (spider flower)
Grevillea robusta is a half-hardy tree sometimes grown as a short-lived, foliage house plant in cool climates. It will not produce its characteristic spidery flowers but the feathery leaves are attractive. Little pruning is necessary apart from the removal of dead or damaged stems. It can also be trained as an unusual wall shrub against a south-facing, sheltered vertical surface, but will need winter protection. In this case, train as a cordon tying in branches to horizontal wires spaced about 45cm (18in) apart up the wall. During June each year, tie in selected new stems at a 45 degree angle each side of the main stem and lower those tied in the previous year to 90 degrees, so that they are in line with the supporting wires. Repeat this process until all the tiers of the main framework are complete, then pinch out the growing tip of each branch when it reaches the edge of the support. Thereafter, shorten any side-shoots to two or three leaves.

Paulownia (foxglove tree)
If grown as a specimen tree, Paulownia tomentosa needs little pruning other than the removal of dead or damaged growth in early summer. Create a clear stem on well-established trees by removing sideshoots when young. However, they also respond well to severe pruning and so can be cut back hard each spring to encourage vigorous new shoots and large, attractive leaves that will add a tropical feel to beds and borders (see March).

SHRUBS

Abutilon vitifolium
Although frost hardy, this abutilon can suffer from winter damage which should be pruned out after flowering. Deadheading spent flowers is also worthwhile.

Buxus (box)
All new box plants should be trimmed back by about half after planting to encourage bushy growth from low down on the plant. Thereafter, formal hedges and topiary should be trimmed this month once the initial spurt of growth is over. Pruning will then produce a sharp and neat outline that will last most of the summer. But if you grow it as an informal shrub, box does not require any routine pruning other than the removal of dead, diseased or damaged growth. If the shrub becomes lop-sided, over-long stems can be cut back to balance the outline. Old and neglected plants respond well to severe pruning and can be cut back to within 15-30cm (6-12in) of the ground.

Carpenteria
This early-summer-flowering shrub bears its blooms on wood produced in the previous season. No routine pruning is necessary, other than the removal of dead or damaged stems as well as any rubbing branches. However if you do need to prune do so immediately after flowering so that new wood has time to mature and ripen before the onset of winter. Mature branches that no longer flower can be rejuvenated by cutting back one-in-three stems to a younger shoot lower down or near
ground level.

Ceanothus (Californian lilac)
Lightly trim ceanothus after planting to encourage a neat habit and bushy growth. Evergreen types such as Ceanothus arboreus ‘Trewithen Blue’, C. ‘Concha’, C. impressus, C. thyrsiflorus do not need routine pruning, but can be kept neat by trimming after flowering each year. Any lop-sided growth can be balanced, by cutting back long shoots by about one-third to a sideshoot lower down. However, evergreen ceanothus is reluctant to produce new shoots from woody stems so avoid pruning back into old wood. Old and neglected shrubs that are well clothed in foliage near the base can have all stems cut back by about half to sideshoots lower down on each stem, otherwise they do not respond to severe pruning and so are best replaced.

Cytisus battandieri (pineapple broom)
Little or no pruning is usually required, other than the removal of dead or damaged stems. Wall-trained specimens will need wayward stems cut back to the main framework and older plants can be rejuvenated by cutting out one of the older stems to a younger sideshoot low down that can be trained up the support to replace it. This is best carried out after flowering.

Escallonia
In the first spring after planting tip back the main branches to encourage bushy growth. Thereafter, little or no routine pruning is required unless you want to restrict growth. In this case prune after flowering. Wall- trained specimens should have flowered shoots cut back to a sideshoot near the main framework of branches that will grow and produce most of the flowers the following year. Escallonia grown as informal hedges can be trimmed now that flowering is over. Bear in mind that the harder you trim the less flowers you’ll get the following year. Old and neglected plants can be cut back hard, but you will loose the flowering display for a few years. If flowering finishes very late you could leave pruning until the following spring.

Euphorbia (spurge)
Popular varieties of euphorbia including E. characias ‘Wulfenii’ and E. myrsinites can have stems that have finished flowering cut back to the first sideshoot that hasn’t flowered lower down on the stem. Take care when pruning and wear long sleeves and gloves to prevent the irritant sap getting in contact with your skin. Old and neglected plants can be rejuvenated by pruning back hard to a stubby framework, but you will miss out on flowers the following season.

Fremontodendron
Little or no pruning is usually required, other than the removal of dead or damaged stems. Wall-trained specimens will need wayward stems cut back to the main framework after flowering. Old and neglected plants do not respond to severe pruning and are best replaced.

Hebe
Dwarf forms of hebe, such as H. pinguifolia, H. albicans, H. brachysiphon and H. rakaiensis, require little or no regular pruning, apart from the removal of winter-damaged stems and any that have died back. Otherwise, simply deadhead the plants by trimming off fading flowers using shears to keep the plants neat and dense. Hedges should be trimmed in the same way.

Helianthemum (rock rose)
Lightly trim rock roses after planting to encourage a neat habit and bushy growth. If they get too leggy and straggly you can cut the whole plant back lightly after flowering using a pair of secateurs. Feed and water well to encourage new shoots and, with luck, a second flush of flowers towards the end of the season. Old and neglected shrubs are best replaced.

Kolkwitzia (beauty bush)
Maintain the flowering performance of the beauty bush by pruning each year immediately after flowering. Cut back flowered stems to a sideshoot that hasn’t produced flowers or to a plump bud. Congested plants can have one-in-three stems removed, starting with the oldest. Old and neglected plants can be rejuvenated in the same way. Established plants tend to sucker and these may need to be removed.

Laurus (bay laurel)
Little or no pruning is usually required, other than the removal of dead or damaged stems. However, you can keep shrubs neat and rounded by pruning new growth back using a pair of secateurs. Bay laurel trained as standards will need any new shoots cut from the main stem. Hedges can also be trimmed at this time of year.

Lonicera (shrubby honeysuckles)
Shrubby honeysuckles, such as the popular evergreen L. nitida ‘Baggesen’s Gold’ and the flowering deciduous L. tatarica can both be pruned now. Evergreen hedges should be cut back by removing about half the new growth each year until they reach the desired height. Thereafter, trim the hedge during May and again in September. Flowering shrubby honeysuckles need no routine pruning, but can be kept neat and flowering well by cutting out one-in-three stems, starting with the oldest, after flowering is over.

Paeonia (tree peony)
No routine pruning is usually necessary, other than the removal of dead flowers or damaged stems. Leggy plants can be reshaped by pruning out one-in-three stems, starting with the oldest, after flowering is over. Avoid drastic pruning on grafted plants.

Rubus (ornamental bramble)
Ornamental brambles, such as Rubus cockburnianus, flower on wood produced the previous year, but are grown mainly for their attractive white winter stems. To get the best flowering and stem displays, remove stems that have flowered at this time of year by cutting them right back to ground level. The young stems left behind will have the best winter colour and will flower the
following summer.

Rosa
Now in full bloom, all types of roses will benefit from regular deadheading as flowers fade throughout the month. Concentrate your efforts on repeat-flowering varieties.

Sophora
No routine pruning is usually necessary, other than the removal of dead flowers or damaged stems. This is best carried out during midsummer when the cuts are less likely to bleed. Wall-trained specimens need tying into their support and any wayward stems cut back or removed completely. Old and neglected plants are best replaced.

Tamarix
Prune early-summer-flowering tamarix, such as T. tetrandra and T. parvifolia, after the blooms start to fade - cutting all stems back by about half of the previous season’s growth.

Viburnum
The deciduous Japanese snowball tree (Viburnum plicatum) and the popular winter-flowering, evergreen V. tinus, can be pruned now. Prune the Japanese snowball tree carefully to preserve the natural tiered appearance. Viburnum tinus does not any need routine pruning other than the removal of dead or damaged stems and the reduction of over-long shoots. Hedges can also be trimmed at this time of year, but use secateurs to avoid leaving cut leaves on the shrub. Viburnum tinus also make excellent standards.

Weigela
After planting lightly trim to encourage bushy growth. In subsequent years, immediately after flowering, cut back flowered stems to a sideshoot that hasn’t produced flowers or to a plump bud – this will help maintain the flowering performance. Remove completely, any all-green shoots on variegated varieties. Congested plants can have one-in-three stems removed, starting with the oldest. Old and neglected plants can be rejuvenated in the same way.

TREES

Juglans (walnut)
English walnuts and black walnuts are prone to winter damage when they are young, so if the main leader is damaged, cut it back into healthy wood and train up another leader to take its place. Do not prune older trees unless absolutely necessary. They are prone to cavities after severe pruning if the collar at the base of the branch is damaged or stumps are left behind. For this reason it is worth raising the canopy when the tree is still young and keeping the stem clear as it grows.

Prunus
All prunus trees are prone to serious disease infection, such as silver leaf, through cuts made while pruning. It is, therefore, a good idea to keep any pruning to a mimimum and to prune only during midsummer when infection is much less likely. Prune out dead or damaged growth and remove suckers. Prune Prunus cerasifera hedges at this time of year too.

Robinia pseudoacacia (false acacia)
False acacia has brittle branches that’s prone to storm damage and in exposed gardens are prone to frost damage. They are best pruned in midsummer because the cuts are slow to heal. No routine pruning is necessary, but remove any suckers as soon as they are noticed. Old and neglected trees are best replaced.

Tilia (lime)
Limes are best pruned in midsummer because they are prone to bleeding if pruned in spring and slow to heal at other times. Most lime trees will form an attractive, well-balanced canopy without intervention and so require no pruning other than the removal of crossing or wind-damaged branches. Young trees should also be encouraged to produce a clear trunk, so remove lower side branches to gradually raise the canopy as the tree grows.

CLIMBERS