Autumn Care for Outdoor Hardy Exotics

September can still feel like summer in much of the UK, but for our outdoor Hardy Exotics, autumn is already beginning. While there may still be plenty of growth to enjoy, plants are starting to prepare for the colder months ahead.

As we move into October, the main concern shifts from keeping plants watered to protecting them from prolonged cold, wet weather. This is when a little preparation can make all the difference, whether you’re growing bananas, tree ferns, agaves or other hardy exotics.

Here’s our guide to the key jobs to tackle over the coming months, and how to give your plants the best chance of coming through winter happily.

Keep going, with one change

Through September the soil is still warm and roots are still active. Keep watering anything in a pot, because containers dry out even in cool, dull weather and a plant that goes into winter thirsty is a plant that struggles in spring. Keep deadheading. Keep an eye out for the last flush of slug damage on soft new growth.

The one change is feeding. Stop nitrogen-rich feed by the end of the first week of September. Nitrogen pushes soft new growth, and soft growth going into the first frost is exactly what gets damaged. If you want to feed at all this late, use something high in potassium, which supports the hardening off of the growth that is already there.

September is also the best planting month of the year for hardy exotics. Warm soil and reliable rain give roots eight to ten weeks to establish before the ground cools. A plant put in now is meaningfully better anchored by March than the same plant put in next April.

October is the month it changes

By October the growing has largely stopped and your job changes from encouraging growth to managing water. Wet is a bigger killer of exotic-looking plants in the UK than cold is. A plant that would shrug off a hard frost with dry roots will rot in a waterlogged pot at four degrees.

Three jobs matter in October. Lift pots onto feet or bricks so they drain freely. Clear fallen leaves out of crowns and rosettes, where they hold water against the plant. And mulch, generously, once the soil is still warm but the top growth has slowed. Our guide to mulching outdoor exotic plants covers depth and materials properly.

The part that matters is the crown and the roots. In late October, pile a thick mulch over the base, at least 20cm, using bark, straw or leaf mould. In colder or more exposed gardens, wrap the standing stem as well. Full method is in our winter protection guide.

The plants that hate wet more than cold

Agaves are the clearest case. Agave iophantha Quadricolor is rated RHS H2, so it is not a plant to leave out in a wet British winter regardless of how mild it is. Move it under cover, keep it nearly dry from October, and it will be fine. Cold is survivable, sodden compost is not.

Cannas sit in the middle. Canna 'Alaska White' is rated RHS H3. In a mild, well-drained garden you can leave the rhizomes in the ground under a deep mulch. Anywhere colder or heavier, lift them after the first frost has blackened the foliage, cut back to about 10cm, and store the rhizomes somewhere frost free and barely moist.

What garden jobs should you do in September?

For a garden built around hardy exotics, September comes down to five things. Stop nitrogen feed in the first week. Keep watering containers. Plant anything new while the soil is warm. Take cuttings of tender perennials as insurance. Order and plant spring bulbs, which want to go in while the ground is still workable.

What jobs should you do in the garden in October?

October is protection and drainage rather than growth. Raise every pot off the ground. Clear leaves out of crowns, rosettes and the centres of grasses. Mulch thickly around anything borderline. Move genuinely tender plants under cover. Cut back only what has actually collapsed, and leave standing stems on grasses and perennials, because they protect the crown and hold structure through winter.

When to actually protect, and why not yet

Almost every autumn casualty in an exotic-looking garden comes from protecting too early rather than too late. Fleece and straw wrapped on in early October, while the weather is still mild and damp, create a warm humid pocket around the plant. That is close to ideal conditions for rot, and it keeps the plant soft at exactly the point it should be hardening off.

Wait for the trigger, which is the first proper frost rather than a date in the diary. In most of southern England that falls in early to mid November, further north and inland it can be late October. Watch the forecast rather than the calendar. The plants themselves will tell you too, because a banana blackening at the leaf edges and a canna going over are both reliable signals.

The exception is anything genuinely tender in a pot, which comes under cover on the basis of the forecast and not the first frost. By the time you have had the frost, the damage is already done.

Wind does more damage than most people expect

Autumn gales cause more visible harm to large-leaved exotics than frost does, and they arrive earlier. Shredded banana leaves and browned frond edges in November are usually windburn rather than cold damage. Two things help. Stake anything tall and top-heavy before the first real blow rather than after, because a rocked root plate is far more serious than a torn leaf. And accept a certain amount of leaf damage as the price of growing big soft foliage in a maritime climate, because the plant is not harmed by it and will replace the leaves next year.

What to leave well alone

Do not prune bamboo in autumn. Fargesia rufa, rated RHS H5, is fully hardy and cutting it now removes the canopy that shelters its own root run. Do not cut back evergreen ferns or Fatsia japonica 'Spiders Web', also RHS H5. Do not tidy grasses to the ground. All of these are spring jobs, and doing them in October costs you both the winter structure and some of the plant's own protection.

Autumn is when the winter garden gets planted

The gap most exotic-looking gardens have is December to February. Autumn is when you fix it, because winter-performing plants need to go in now. Sarcococca hookeriana var. digyna, rated RHS H5, is a shade-tolerant evergreen that flowers from December to March and is powerfully scented at a time of year when nothing else is. Trachycarpus wagnerianus, rated RHS H5, holds a full evergreen crown through the worst of the weather and carries the tropical look right through winter.

Both are in our hardy exotics range, and every dispatch is protected by our live arrival guarantee.