One hears again and again that wood ash can be used as fertilizer in the garden. We will show you what you should consider when fertilizing with ash.
Wood ash contains many nutrients, but unfortunately it is not used for fertilization far too often. That's a pity, after all, the recycling of nutrients is an important component of sustainable agriculture and garden culture. To enable you to use it, we have compiled all the necessary information on using wood ash as fertilizer.
Many stove and fireplace owners are unsure whether ash can even be used as fertilizer. We answer this question and then explain the effect, the correct application and explain which plants can benefit from fertilizing with ash.
Can you use ash as fertilizer?
Not every type of ashes can be safely distributed in the house or garden. Plant ashes are basically suitable to be used as fertilizer - this means ashes from burned wood, straw or other plant material. Normally printed, non-glossy paper is also suitable, so that the ash from your own fireplace can be used - provided only untreated wood has been burned. Ashes from briquettes, coal, treated wood and glossy printed paper must not be used. Because these materials contain substances that should not get into your garden soil.
How does ash work as fertilizer?
Ash has a pH value of 10 to 13, it contains a lot of alkaline acting calcium and magnesium.
| Contained Nutrient | Concentration in untreated wood ash |
|---|---|
| Calcium Oxide (CaO) | 26 - 40% |
| Phosphorous Oxide (P2O5) | 4 - 7 % |
| Potassium Oxide (K2O) | 7 - 12% |
| Magnesium Oxide (MgO) | 3 - 5% |
| Other trace elements | In variable proportions |
| Nitrogen (N) | Not included |
The inNutrients contained in plant ash are readily available: If they were still surrounded by organic carbon packaging before incineration, this oxidized during incineration and escaped as CO2. The calcium oxide it contains is also referred to as burnt lime. When burned, this form of calcium is also easily soluble and acts quickly. It is therefore also suitable for liming heavy, clay-rich soils. Quicklime reacts with water in the soil, increasing the pH of the soil solution and releasing calcium. It is now ready for uptake by plant roots. Incidentally, if the humus content is sufficiently high, calcium acts as a kind of electrical bridge between humus molecules and clay minerals, thus enabling the formation of stable soil crumbs. And these are a real blessing for many soil properties, one speaks of the so-called lime fermentation. It should be noted that ash contributes neither organic material nor nitrogen. It can be considered as a nitrogen-free mineral fertilizer with a very high pH.
Tip: Because quicklime is all too easy to cover light, sandy soils, it is better to use carbonate of lime - for example from egg shells.
Summary: How does ash work as a fertilizer?
- Ash is highly alkaline and can raise soil pH very quickly
- The contained plant nutrients are readily available - however, there is no nitrogen
- Light soils are easily calcified with ash, so the pH is raised too quickly and too much. Ash can be used on heavy, clayey soils
- The released calcium promotes the formation of stable soil crumbs (calcareous sludge)
Which plants can be fertilized with ash?
The alkaline effect of ash should by no means be underestimated: Precisely because quicklime is so easily soluble, there is a significant risk of overliming. A massive increase in the pH value due to a too generous distribution of ash can mess up the soil chemistry in such a way that the plants growing there can no longer absorb nutrients, are stunted in growth or even die, at least for a short time. This is especially true for plants that are actually used to acidic soil: rhododendrons (Rhododendron), blueberries (Vaccinium myrtillus ), checkerberries (Gaultheria), ferns and many wood perennials, for example. lime loversPlants and those with high calcium requirements tolerate ash better and may even benefit from it. In the following table we have put together a selection of lime-loving plants. You can find another selection of lime-loving plants in our special article on fertilizing with eggshells.
| Lime-loving perennials | Lime-loving shrubs |
|---|---|
| Silver avens (Dryas x suendermannii) | Various maple species (Acer campestre, Acer negundo, Acer platanoides,Acer pseudoplatanus etc.) |
| Globe Thistle (Echinops ritro subsp. ritro) | Hornbeam (Carpinus betulus) |
| Carpetal Spurge and Colorful Spurge (Euphorbia myrsinites / Euphorbia polychroma) | Deutzia (Deutzia in their types and varieties) |
| Wild Strawberry (Fragaria vesca var. Vesca) | Ivy (Hedera in their species and varieties) |
| Woodruff (Gallium odoratum) | Nacre Shrub (Kolkwitzia amabylis) |
| Blood Cranesbill (Geranium sanguineum) | Philadelphus / False Jasmine (Philadelphus in its species and varieties) |
| Gypsophila (Gypsophila paniculata) | Woolly, Common, Japanese and Tongue Viburnum (Viburnum lantana, Viburnum opulus, Viburnum plicatum , Viburnum rhytidophyllum) |
Application of ash as fertilizer
Because of the strongly alkaline effect of ash, a pH test of the soil should always precede its use. If your garden soil is only slightly acidic, neutral or even slightly alkaline, ash should be used cautiously or not at all. If pure ash gets on plant parts, it will burn the plant tissue. Because plant ashes do not contain any nitrogen or organic material, supplementary fertilization should definitely be used to provide for the plants. Organic long-term fertilizers are best suited, including our Plantura organic fertilizers - such as the Plantura organic universal fertilizer.
Basically:
- Spread ash when there is no wind: This prevents lime-sensitive plants from being damaged elsewhere in the garden
- Wear gloves when spreading ashes as the high pH will damage your skin
- Moistening the ash reduces dust formation
- Water thatSoil after application
- Never apply ash in connection with fertilizers containing ammonium such as liquid manure, manure or mineral nitrogen fertilizers - gaseous ammonia would be produced
- Never apply ash in combination with mineral phosphates or fertilizers containing phosphate - calcium phosphates would be formed which are difficult to dissolve and no longer available to plants
Remember that most garden soils do not require lime or calcium, as minerals containing calcium are found in almost all locations. The use of ash or lime is usually only necessary for planting with plants that expressly love lime or for peat-based potting soil. After a few years, peat soil placed in pots and beds is often very poor in calcium, since peat naturally contains almost no calcium.
How much ash to use as fertilizer?
On heavy, acidic soils (pH 4), 200 to 400 grams of plant ash per square meter can be applied every three to four years. Less acidic soils can be treated with 100 to 200 grams of plant ash every three to four years. You should not spread ash on light soils, as limescale can quickly occur. It is better to use ground egg shells as fertilizer, the effect of which we will explain to you in more detail in this special article.
Tip: Another use for ash is in your home compost heap. Since microorganisms become more active at high pH values, composting can be accelerated by adding ash. However, more volume of the compost is lost in the process than if the composting took place without lime. If possible, only use ash if you want to compost acidic compost: Oak leaves, pine wood shavings or peat soil can be dusted with a thin layer of ash.
Summary: Application of Ash as Fertilizer
- The use of ash only makes sense for lime-loving plants, peat soils or soils that are proven to be too acidic or low in calcium. The latter is very rare
- Ash should not get onto plant tissue undiluted, as it can cause burns
- Since ash contains no nitrogen, additional fertilization with an organic slow-release fertilizer is necessary
- Ash can also be spread on the compost on acidic rotting material to avoid itsBalance pH
If you want to learn more about using natural fertilizers, see our review article for more reading.
Since ash alone is not enough to cover the entire nutrient requirement of the plant, we recommend that you also fertilize with an organic long-term fertilizer. Due to their primarily organic raw materials, our Plantura organic fertilizers optimally supplement natural fertilization with ash and ensure a long-term supply of nutrients.