If you heat with wood and/or coal in the winter months, you can not only enjoy cozy warmth, but you also have to dispose of a lot of combustion residue. Our grandparents used ash directly as fertilizer and added the fine powder to the compost. But is this still relevant today and does ash actually have a fertilizing benefit?
Can you use ash as fertilizer on compost?
Ash in compost can have fertilizing benefits in small amounts as long as it comes from untreated wood. However, you should be careful with larger quantities, as heavy metals and high pH values can unintentionally pollute the garden soil.
Wood ash in natural fertilizer should not be viewed uncritically
According to experts, disposing of large amounts of wood ash in the compost is not entirely unproblematic. This is due to the composition of the gray powder.
Wood ash consists of:
- 25 to 45 percent quicklime (calcium),
- 3 to 6 percent magnesium and potassium oxide,
- 2 to 3 percent phosphorus pentoxide,
- as well as traces of iron, manganese, sodium and boron.
- Depending on the origin of the fuel, there may also be heavy metals such as cadmium, lead and chromium. Sometimes even in critical quantities.
That's why ash should only be used very sparingly as fertilizer in the garden. If you compost all of the ash produced in your household, the valuable fertilizer will inevitably accumulate on one side with the substances mentioned above.
What impact does this have?
Due to the high pH value, this fertilizer would no longer be optimal for the garden. Spreading the compost is like liming the soil. In agriculture, such fertilizers are only used to improve bare, very clayey soils.
In addition, without analysis you will neither know the exact proportions of trace elements nor how high the heavy metal content is. This can lead to you unintentionally enriching the garden soil with toxic substances.
Less is more
As is often the case in this case: a little ash in the compost can improve the quality. However, too much must be avoided at all costs. The following applies:
- Only add ash from untreated wood to the compost. Varnish, glue or the plastic coatings of glossy magazines can contain dangerous, toxic substances.
- Only use firewood whose origin you know. If the tree was on a busy road or in an industrial area, toxic heavy metals may have accumulated in the bark and wood.
- Natural fertilizer enriched with wood ash is ideal for loamy or clayey soils. This fertilizer can help you get the high pH values under control.
- Sprinkle just a fine layer of the gray powder into the compost and cover with a thick layer of green material.
Tip
Ash from the charcoal grill should always be disposed of with household waste. This ash contains fatty residues, such as the discredited acrylamide. These substances have no place in the garden soil.
