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Growing Potatoes Under Straw Mulch

Growing potatoes under straw mulch is much favoured by organic gardeners using a no-dig system. Sadly, ‘no-dig’ does not mean ‘no-work’ but this can be an easy way to obtain a clean crop of potatoes.

Growing Potatoes Under Straw MulchIf you can get hold of a supply of straw that has not been treated with a selective herbicide (usually organic) at a reasonable price it’s worth considering growing potatoes under straw mulch but do be aware of the potential problems below.

Problems with Growing Potatoes Under Straw Mulch

One large drawback to this system in my experience, it seems to attract slugs. If you have a heavy slug population then you are going to have to take measures to protect the crop from them.

The other drawbacks to this system are that the plants are more vulnerable to frost and wind. Because of frosts you may not be able to plant as early as your neighbours using conventional methods.

Laying horticultural fleece over the straw potato mulch will certainly help if the weather turns cold and ensuring the fleece is held in place will also stop the mulch from being blown off in a storm.

If the straw has been treated with a selective herbicide then the straw mulch may poison your potatoes and your plot.

Some gardeners report a reduced yield with this method although others feel the yield of undamaged, first-quality tubers with clean skins is increased.

Some weeds, particularly bindweed, thrive under the mulch.

How to Grow Potatoes Under Straw Mulch

You start by hoeing off the soil, removing any perennial weed roots to achieve a clean surface. Then spread well rotted manure or good compost over the soil, aiming for at least 5cm depth.

Standard Spacing For Potatoes

  • First & Second Earlies 30cm apart in rows 60cm apart
  • Maincrop 40cm apart in rows 75cm apart

If you haven’t any manure or compost, then break up the surface by lightly forking and then apply some proprietary potato fertiliser or even a general purpose fertiliser like fish, blood and bone. Potatoes do need feeding well to produce a good crop.

Just lay your seed potatoes on the surface at the normal spacing and cover with 5cm of straw. As the potatoes start growing you may need to help the foliage through the straw.

Some French trials indicate that planting the seed potatoes about 8 cm deep, about half normal planting depth, results in improved yields.

Top up with more straw as they grow and when the straw mulch is about 20cm thick, cover with a thick layer of grass clipping or partially rotted leaves. This will stop any light getting to the tubers and help hold the straw in place in case of windy weather.

If tubers do appear through the mulch, just add more straw to keep them covered. Care must be taken or you could find exposed tubers going green and inedible.

As with conventionally grown potatoes, ensure you water well in dry periods. Feeding with dry fertiliser is more difficult but liquid feeds can be applied after the potatoes are straw mulched.

Harvesting Potatoes Grown Under Straw Mulch

With your first early potato crops, you will find you can just move the straw aside, pick your potatoes for a meal and leave the rest to grow on. Harvesting is certainly far easier than with the conventionally grown system. No digging, just move the mulch aside and pick up the crop.

After Cropping Straw Mulched Potatoes

The mulch can go onto the compost heap along with the haulm, providing balancing ‘browns’ to the ‘greens’ in your compost.

Alternatively the straw can be dug or rotavated into the soil to add humus. This will deplete nitrogen in the short term so balance with fertiliser if planting a follow on crop.

Caution!

Often potatoes are used to break in new plots. The thing is it is the conventional cultivation that breaks up the soil. Surface planting on compacted, poor soil – especially clay soils – will most often result in very poor crops.

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