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How to improve your soil in autumn

Val Bourne / 09 October 2018

Autumn is the ideal time to start giving your soil some attention in time for next year's spring planting.

Autumn leaves
There's no shortage of fallen leaves in autumn, and luckily they make one of the best soil improvers there is

Autumn is the perfect time to improve your soil, because you’re bound to have lots of woody stems and leaves that either need cutting down or collecting. Don’t put them in the green bin unless you really need to, because you can make soil-enriching leaf mould and friable garden compost that you can use in several ways. There is still time to plant annual green manure crop and these will germinate and when they reach about 6 inches in height it’s possible to dig them in and this will feed the soil.

Most of us will never produce enough leaf mould or garden compost to apply to the whole garden, so the trick is to target certain areas such as vegetable beds, or woodland areas.

In any case lots of plants prefer poor soil and these include many sun-loving plants such as lavender, dianthus, sages and thymes. Over feed these and they’ll flop and fail to flower.

In this article

Making leaf mould
Garden compost heap
Making comfrey tea
Double digging
Winter digging
Planting green manure

Using autumn leaves

Most gardeners find themselves picking up leaves at this time of the year and you can’t add lots of them to the compost heap because they take far too long to rot down. It’s far better to use them for leaf mould. You can create a square structure made from chicken wire or wood on the outer edges of the garden. Or you could use one of those square rubble sacks, the sort sand is delivered in. If space is tight, black plastic sacks could also be used, although you have to punch some holes in the sides. Make a stack behind the shed.

Shredding and mowing leaves

Left to their own devices leaves may take two years to rot down, but you can speed it up by turning the leaves over and then it could be ready in about a year. Some gardeners speed up the process by running over their leaves with a mower before they add them to their leaf bins. Or you can use a shredder and this is one of the most useful bits of garden kit you can have if you’re into recycling. It will not only break up your leaves it will also shred woody stems and these can be added to the compost heap.

Evergreen foliage takes years to rot conventionally because it tends to be tough and leathery so this certainly needs chopping up with a shredder or mower. Some deciduous leaves are leathery as well and these include walnut, sycamore and horse chestnut so these also need chopping up. The best leaves at rotting down quickly are hazel, hornbeam and beech so these do not need chopping up. Pine needles make acidic leaf mould which is very useful for ericaceous plants such as rhododendrons, azaleas and blueberries. Conifer foliage should not be added to leaf mould bins, although that could be shredded and put on the compost heap.

Speeding up the leaf rotting process

The secret ingredient is water because damp leaves rot down far more efficiently so you may have to water your leaf bins to speed up the process. If you’ve got lots of leaves on the lawn it’s far better to mow over them and pick them up and try to rake them up.

The perfect tool for the job

Picking them up in the border is far easier if you use a rubber rake and Bulldog Tools stock a very good one. It is possible to rake over plants with the rubbery tines without causing damage.

The older the better

Leaf mould is rather like vintage wine, the older it gets the better so try to leave it for two years so that it resembles crumbly chocolate. This is the best soil conditioning mulch the amateur gardener can make and it should be used as round choice woodland plants, such as trilliums, or put round special trees and shrubs. It’s laid on the surface in autumn and early winter and you don’t have to dig it in because there are no weed seeds. Some gardeners even use leaf mould as a potting compost, but I prefer to lavish it on my choice plants.

Garden compost

You’ve probably got a full compost heap at this time of year, full of stems and vegetable waste. This will rot slowly at a low temperature and it will take almost a year. It will not kill off weed seedlings or seeds from over enthusiastic perennials, so garden compost is generally put into a trench, or dug in. It needs to be well-rotted before it’s used so it’s worth watering your compost heap well at this time of year and covering it up with cardboard, or a tarpaulin. Then it will carry on decomposing during the winter months when it’s warm enough.

Find out how to create a compost heap

Speeding up your compost heap

You can speed up the decomposition process by adding chicken, rabbit or hamster droppings. You can also add animal bedding. However dog and cat faeces should not be added for health reasons and because it makes the compost very acidic.

No compost heap? Use green waste

Many counties recycle green waste on a weekly basis and it’s rotted down under heat and sold back to the public in bags, or in bulk. The heat process kills weed seeds and plant diseases. Although it’s a good option for most gardeners because it’s cheap to buy and it aerates and fertilises the soil, it isn’t strictly organic because green waste contains chemical residues.

It can be added to the ground as a mulch, because there are no weed seeds to worry about, and it can be dug in as well. You can use it on flower and vegetable and this worthy process stops leafy material going into landfill.

Grow some comfrey

Comfrey leaves also speed up compost making and you can cut them and add them in layers about once a month. The best clone is Bocking 14, often available from seed companies as plants, because this sterile clone doesn’t produce seeds. The leaves also make good compost tea.

Comfrey tea recipe

Put chopped comfrey leaves in a container with a lid and leave them to rot for a couple of weeks. No water is required.

As the leaves decompose they produce a brown liquid called comfrey tea. This can be diluted one part comfrey tea to twenty parts water.

Use it in the same way as you would water-on tomato feed.

Find out more about growing and using comfrey

Double digging

Lift one spit (spade depth) of soil with a spade and place it on a tarpaulin.

Break up the bottom of your trench with a garden fork.

Add the compost and spread into the trench to a depth of 6 to 8 inches.

Replace the garden soil to form a mound.

As decomposition continues the soil level falls and the temperature rises helping hungry vegetables, such as brassicas, to grow.

Do this in the winter to give the soil time to settle.

Don’t plant carrots and parsnips on these beds, the enriched soil won’t suit them.

A double digging tip

Dividing your vegetable garden into 8 x 4 beds makes double digging less challenging.

Winter digging

Winter digging is very valuable because it helps to break up the soil and it also brings pests such as like slug eggs to the surface so the birds can eat them.

Use a garden fork and turn the soil over WITHOUT breaking up any of the clods. As the ground freezes and thaws the clods disintegrate to produce a fine tilth. The only thing you need to do us rake and level the ground.

Winter digging tip

The golden rule when digging is not to tread on the soil, because your weight will compact it. Short scaffold planks are ideal for standing on and not too heavy to move.

Planting green manures

This is another method of incorporating leafy material into the ground. The crop is sown in early to mid autumn as scattered seed and will germinate between autumn and spring. Annual green manures are dug in when they reach 4 to 5 inches in height, before they flower. They include mustards, grazing rye grass, phacelia and some clover mixtures.

Most green manures need to be left on the ground for more than one year because many of them are leguminous members of the pea and been family. Their roots have nitrogen-fixing nodules. Lucerne or alfalfa, for instance, is left in the ground between two and four years. This technique is more useful on an allotment, or in a large garden, but difficult if you’ve got a small plot.

Find out more about green manure

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The opinions expressed are those of the author and are not held by Saga unless specifically stated. The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.