Improving Soil with Wood Ash

Reader Contribution by Benedict Vanheems

Improve Your Soil Using Wood Ash

Wood ash is a valuable source of plant nutrients, which makes it very useful in the garden. It’s high in potassium, which encourages flowering and fruiting, and also contains phosphorous and a variety of micronutrients including manganese, iron, zinc and calcium.

Ash from hardwoods such as oak contain more nutrients than ashes of softwoods like as pine.

You can also use ash from lumpwood charcoal, but avoid using the ash from coal or treated timber as this may harm your soil and plants.

Composting Wood Ash

Adding wood ash to your compost heap helps to reduce the acidity of the compost slightly, making it perfect for mulching around vegetables. It also creates better conditions for the worms that help create compost.

Add a few handfuls or a shovelful of wood ash to your compost little and often, in thin layers.

Adding Wood Ash to Your Soil

Test your soil if you don’t already know its pH. Wood ash is alkaline, and most vegetables need a pH of 6.5 to 7.0, so if your soil’s below 6.5 wood ash can help increase it slightly. As a general rule, apply about two ounces of ash to every square yard. Scatter it over the surface on a still day, wearing gloves to protect your hands, then rake or fork it in.

Use wood ash to improve soil for brassicas such as cabbage and Brussels sprouts that prefer a more alkaline soil. You can add it to the soil the winter before planting or spread it around plants that are currently growing.

Wood ash is beneficial used around fruit bushes, including currants and gooseberries, and fruiting vegetables such as tomatoes, due to its high potassium content. It helps improve fruiting, disease resistance and hardiness by helping wood to ripen faster.

Don’t let wood ash come into contact with seedlings, and avoid using it around acid-loving plants such as blueberries. It shouldn’t be used on soil used to grow potatoes, as alkaline soil can encourage potato scab.

You would need to add a huge amount of wood ash to make your soil too alkaline for most crops, but do re-test your soil’s pH every couple of years to make sure it doesn’t go above 7.5.

Wood ashes need to be kept dry so that its nutrients don’t wash out. Use a container with a close-fitting lid to keep ash dry until you’re ready to use it.

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