A few helpful tips for autumn trimming.
What has to go?
All dead and diseased wood (branches with brown rot on red cherry trees, nectria canker on maples etc.)
Competing branches if they chafe each other and cause bark injuries or have the potential to do so
Anything which gets in the way and could prevent people from safely using winter path
Soft top shoots and their undeveloped buds, buds that have blossomed and any seed stems (e.g. on blue mist, perovskia, roses, and butterfly bushes)
Dead leaves on bushes and grasses. But: Over-mature or snow-covered grasses and bush seed stems can look very pretty in autumn/winter gardens, particularly when lit with GARDENA garden lights. In addition, garden insects spend the winter in hollow straws and seed stems. You should therefore assess the situation and possibly cut them down in the spring, instead.
What to leave?
You should cut with restraint at this stage. Frost can damage cuts but can also freeze back branches. So if you now cut back to the spring level and the plant suffers frost damage, you will have no freedom left to correct it in the spring. Cut less away now so that your freedom to care for your plants is not restricted in the spring.
Notes on certain popular varieties
Box hedge: Box is an evergreen and maybe at risk of frost. You should therefore only cut it into the desired shape in spring. Box can cope with with being cut down to the old wood in the spring and will then push itself out again. When it starts to push out, apply a little fertiliser and reshape when the branches are around 5 cm long. See also > Hedge plants
Cotoneaster: Floor-covering cotoneasters are very resistant to frost. They can now be shaped to suit the planting area with a hedge trimmer. The plant will withstand being cut back to the old wood but this is best done in spring. Young plants should be trimmed in spring to half of the branch length of the previous year for a more compact structure and better branching.
Yew: Can handle being trimmed extremely well, even right down to the oldest wood. You should ideally cut it back in spring because conifers act as wind breakers in winter gardens and offer protection for birds.
Lilac: Hardly needs to be trimmed. Often responds to trimming with strong growth which can also mean wild branching in the dressing area. Handles being trimmed down to the oldest wood; best done in spring. If you decide to cut it back, trim the older branches and twigs to an even length all around. If you want to promote new growth, cut free the long branches in the middle; do not shorten them, Only leave the strongest 5-7 of these. Cut back older bushes to 30-50 cm if necessary in order to regenerate the bush through new growth in 2-3 years.
Fig: Trim in spring since it can freeze easily. The fruits for 2009 can already be seen on it. You should therefore only cut it back a little in spring. Then mainly concentrate on the shape and on thinning it out. Like quince trees, figs do not respond sustainably to pruning. They do not branch better if you trim the one-year top shoots. Only one-year long branches can be encouraged to branch if they are cut back in a suitable place.
Grasses: You do not have to cut them back right now; instead, rope them together if necessary and cut them in spring. This protects the heart of the plant from frost and winter moisture as is required, for example, for pampas grass.
Hedges: Do not cut now in the autumn! Young hedges: First cut in May/June, second cut in August/September. For old hedges, one cut after their second flush (at the end of June) may be enough. It is best to cut conifer hedges before they shoot so that the wounds heal quickly. Some German states issue guidelines on when to cut hedges (to protect breeding and young birds). For more information, ask your local authorities (parks and gardens department and conservation authority). When cutting hedges, try to shape sloping sides to prevent the bottom quarter from becoming bare. For each 100 cm as you move upwards, each side should be 10 cm further in (i.e. a total of 20 cm narrower).
Currant bushes: In 2009, the light 2008 shoots with a thickness around that of a pencil will bear quality fruit; these shoots should be released by trimming (in spring). At the same time, trimming should also promote the 2009 shoots (i.e. the fruiting branches of 2010). Thin out the bushes by removing thick, dark growth which is more than 3 years old (just above the soil or at soil level if the branching is good). Trim the bushes by cutting back shoots to the level of branching required. Only leave 5 to 7 of the strongest soil-level shoots and do not shorten them.
Cherry trees: Thin out ornamental cherry trees in spring after they blossom. Fruiting cherry trees should be trimmed immediately after the harvest in June/July. Only cut/thin them out a little! Trimming too heavily will cause gum to flow, which can kill the plant after a few years.
Kiwi trees: Leave around three to seven side branches on the main vertical branch (depending on the support system supporting the kiwi tree); these are the main branches which will bear fruit. The buds of fruit bearing branches will grow from these main branches. Shorten these in the summer to around eight to ten leaves starting from the first leaf above the fruits. In late winter, shorten the same branches to three to five buds and new fruiting branches will sprout from here again. Every three to four years, remove this ageing branch complex right at the main branch and replace it with a young fruit branch.
Corkscrew willow: Best trimmed in spring; in the winter the thinner branches in particular freeze back. You will notice this in spring and can remove them. This tree can cope with both light and very heavy trimming, even down to the old wood.
Privet: Handles trimming extremely well, even down to the old wood just a hand's width above the soil. Otherwise the same applies as for hedges.
Olive trees: Best trimmed in the spring. Then thin out by removing older growth or branches which are too tightly packed. Reduce the shoot length by trimming back to another branch deeper in and round off evenly. Handles very heavy trimming down to the oldest wood in spring. The olive tree handles very strong cuts by pushing out long shoots. Thin these out to a few structural branches.
Plum trees: Do not trim in autumn; cut back in late winter before the buds swell in March.
Rhododendron: Shorten the branches when blossoming ends, trimming back to a favourable lower branch. Alternatively, trim back to the old wood; strong rhododendrons handle trimming very well.
Roses: Cut all flowerbed roses and climbing/bush roses back by a third. Finely trim in spring. Leave the rose hips on wild roses as decoration and thin down in spring rather than cutting them now.
Japanese umbrella pine: Does not handle trimming well; only trim in spring due to sensitivity to frost. Then cut back a shoot to a favourable twig. This makes the shoot shorter but a green frond remains as tension wood.
Snowball tree: Except for the Guelder rose, only trim in spring. Otherwise, trim in the same way as > Lilac.
Buddleia: In autumn, only shorten by a third to a half; do not cut back more than this to prevent frost damage (see above). Trim finely (thin out and reduce by around 50 cm) in March/April before growth starts.
Citrus trees: Only cut in spring; then thin out and round off evenly if necessary to encourage new growth and a large amount of blossom (e.g. oranges blossom on one-year old wood).
Angel's trumpets: Only trim a little before winter. The more you cut back now, the later the plant will bloom in the new year because the blossom growth has to form first.
Blue potato bush: Trim by a third now and prune structurally in spring. Can then be cut back to the old wood.
Oleander: Handles trimming very well; can even be cut back to the old wood in spring. However, it is always better to trim back to a fork so that leafy shoots remain as tension wood. Please also note that different varieties of oleander branch better than others after pruning. Oleander should normally be trimmed immediately after blooming. If you cut it back now in autumn, you could remove the buds for the coming year.
Lantana camara: As for blue potato bush
Citronella: Citronella plants are not usually cut back because they get more beautiful from year to year. However, if necessary you can cut back a good hand's width. This is best done in spring.