10 tips for autumn planting

Planting for the future, like any gardening task, requires skill and understanding, though plants in some situations can be more forgiving – for example, the odd bulb planted upside down will still perform, but a badly planted tree may never succeed. Given plants cost money, it makes sense to invest time to get the planting technique right and guarantee success.

More advice on how to plant:

• Complete guide to bulb planting
• How to plant perennials in autumn
• Plants to give borders an autumn boost

Discover our 10 tips for autumn planting success, below.

Plant at the right time

Timing is key to autumn planting. While the soil is typically warm and moist, conditions may suddenly turn very cold, so it's important to check conditions ahead of planting. What's more, exotic or frost-tender plants need more time to establish than hardy plants, so are best planted in the spring, instead.

As a rule, the sooner you plant your plant, the better. Spring-flowering bulbs and bare-root shrubs and trees should be planted as soon as you buy them.

Buy healthy plants

Look for plants that are well established in their containers but haven’t been sitting around for years in the same pot. Roots appearing out of the drainage hole that are fibrous, white and fresh-looking are a sign of a vigorous plant ready to go in the ground – thick woody roots indicate a plant that’s been in its pot too long and may not establish once planted. With bulbs, look for plump bulbs, free of mould or shrivelling. Peeling outer layers are normal and of no concern.

Save money

It’s well worth prioritising your budget and choosing smaller plants rather than splashing out on larger specimens. Many quick-growing plants, such as perennials and grasses, can be bought in good-value, small pots and usually establish quickly and easily. Expect larger plants to take longer to settle and establish, and avoid planting large trees that are severely pot-bound as they may never stabilise properly.

Larger trees and shrubs also need longer aftercare and may not start growing normally for 18 months to two years after planting. So, unless you want a more established look from day one, save your money and buy younger specimens that need less care and will establish more quickly.

Prepare the soil well

Fertile, well-cared for soil needs little more preparation than digging a hole that the plant will sit in, whereas compacted soil needs digging over and breaking up with a fork to aerate it first. For trees and large woody plants, dig a square hole three times the width but the same depth as the pot, and if the soil is a sticky clay, puncture the sides of the hole with a fork. Loosen the base of the hole but do not add organic matter. It will rot down and cause the plant to sink – instead keep the organic matter for a surface mulch once you’ve finished.

Use friendly fungi

Mycorrhizal fungi helps establishing plants to build successful underground networks for better uptake of moisture and nutrients. In established gardens, these networks often already exist and this process will happen naturally over time. But you can speed up the process by adding friendly fungi when planting.

Apply to young, active roots rather than just scattering it in the planting hole and ensure the product is stored correctly and used within the use-by date.

Help root development

Teasing out roots can help plants develop quickly and encourage roots to grow outwards faster, as opposed to remaining in a confined space. Ideally, don’t buy severely pot-bound plants, but don’t worry about ones that have masses of fibrous roots, such as heathers and hebes, and appear pot-bound. Lightly rubbing over the rootball with your hand or raking over the edges with a hand fork is usually all that’s needed.

With trees, especially bare-root ones, try and ensure any major roots are directed outwards, away from the stem, as opposed to curling around within the planting hole. Finally, avoid the vigorous root disturbance of any plants that hate being moved, such as daphne and edgeworthia.

Provide support

If a tree is stable after planting, don’t stake it. If there is a chance of the wind loosening it in the planting hole, insert a low stake at a 45° angle, ensuring the prevailing wind blows the stem away from the stake as opposed to knocking into it. A well-placed stake should allow the stem to flex in the wind but the rootball to stay stable. In most cases, stakes can be removed after 12-18 months. If the tree is still unstable after this time it could be establishment failure, typical with planting root-bound stock.

• How to plant a tree

Plant at the right depth

The rule of thumb for planting bulbs is 2-3 times the depth of the bulb. A bulb such as a crown imperial needs at least 30cm depth or it will not flower reliably.

With woody plants, the root flare (the point where the first roots emerge from the stem) should be placed at soil level. This is especially essential with trees as planting them too deeply is a common cause of death. If the root flare isn't visible, scrape the compost back until you can see it.

Mulch around plants

After planting trees or shrubs (or herbaceous plants in poor soil) apply a generous mulch. This can be manure, bark chips or homemade compost as it helps to seal in moisture, and adds slow-release nutrients as it breaks down. Never heap mulch around the base of a tree – the all-important root flare must be visible. Apply a thick ring around the base of the tree, about 15cm deep.

Never apply mulch on frozen or dry soil, always water thoroughly first, then mulch.

Soak plants before planting

Never plant dry root balls – spend time watering plants beforehand and, if in doubt, dunk the plant in a bucket of water for at least 10 minutes. Once planted, evergreens may still require watering during winter in dry spells as they lose water through their leaves. Continue watering new plants through their first summer season, possibly longer on sandy soils or in drought-prone areas.

Watering is most effective first thing in the morning or last thing at night, and applied directly to the soil slowly but consistently.