Can Ash Be Used As Fertilizer?

If hobby gardeners own a fireplace, it is reasonable to assume that they will continue to use the wood ash. After all, these are the remains of organic material. But if you want to use ash as fertilizer, there are a few things to consider. Wrong use can have negative consequences.

If the wood is completely burned, the remaining ash from the fireplace or tiled stove is disposed of directly in the residual waste in most households. It contains all kinds of concentrated minerals from the original plant tissue. Therefore, if you want to use ash as fertilizer for the plants in the garden, you shouldn’t act too quickly. Because the black powder is not suitable for all plants. As a general rule, you should only use ashes that have been proven to be untreated. The ashes from charcoal are not suitable as they contain all kinds of additives.

How does ash work as a fertilizer?

Ash is very basic and therefore has a very high pH value. For this reason, ash should only be used as a fertilizer for lime-loving plants as well as lime-poor and acidic soils. It is advisable to carry out a soil analysis beforehand in order to find out the corresponding pH value.

If you fertilize with wood ash inadvertently, you can damage the plants and the soil. Ash must also never come into direct contact with the plants or in its pure form, as the fabric can be corroded. In addition, ash does not contain any nitrogen, as it escapes during combustion. Therefore, ash cannot replace a nitrogenous plant fertilizer. Ash contains the following components:

  • calcium oxide (quicklime)
  • magnesium oxide
  • potassium oxide
  • phosphorus oxide
  • various trace elements (iron, sodium, manganese etc.)

Is any ash suitable as a fertilizer?

Ashes are not created equal – and should not be used as fertilizer in every case. In general, plant ash is suitable as a fertilizer – if it comes from untreated wood. However, you should not fertilize every soil with ash. It is also advisable to use only small amounts of it. The motto “a lot helps a lot” is generally out of place with fertilizers. The charcoal from the barbecue area has no place in the garden bed – there can be many pollutants in it that you can neither detect nor filter out.

Tip: After applying the ashes, you should water the soil thoroughly so that the material can bond well with the soil. In addition, ashes should not be touched with bare hands, but gloves should be worn as this can cause chemical burns.

Which plants can be fertilized with ashes?

As ash is highly alkaline, it is not suitable as a fertilizer for all plants and soil conditions. If a pH test shows that the soil is neutral or even slightly basic, you should refrain from fertilizing with ash. If, on the other hand, it is acidic, ash can neutralize the pH value again. The following lime-tolerant plants, among others, tolerate ashes fertilization:

  • Useful plants: grapevines, gooseberries and raspberries, tomatoes, Brussels sprouts, leeks, rosemary, salsify, onions
  • Ornamental plants: geraniums, fuchsias, roses, gladioli, phlox, lavender, boxwood

Can you fertilize the lawn with ashes?

If the lawn is too acidic, you can counteract this with a little ash. However, you should make sure that it is natural wood ash without additives so as not to damage the lawn.

How often should you fertilize with ashes?

In general, you should be very careful with ashes if you want to use them as fertilizer. A small amount is enough to change the pH value. If the soil is very acidic with a pH value of 4 or lower, you can spread around 300 grams of ash per square meter every three years. In less acidic soils, half the amount should be used. With neutral or even alkaline soils, you should stay away from the fertilization method.

What does ash do on the compost heap?

Ash can also be used on the compost heap at home. The background: the micro-organisms are more active when the pH value is lower. So with a little ash you can speed up the rotting. However, you lose the amount of compost. It is best to use ashes on the compost with acidic rotting material such as coniferous wood chips or oak leaves.

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