Egg shells don't have to go to waste, they can serve as a source of nutrients for plants. We explain how to use egg shells as fertilizer.
On average, a German eats 245 eggs a year. The resulting egg shells usually end up in organic waste. However, some resourceful gardeners value the shells as fertilizer. We will explain what effect eggshells can have and how exactly they should be used.
After introducing the ingredients and the effects, this article will explain the correct use of eggshells. It is also important that only the right plants are fertilized with them. Therefore, the last paragraph presents a selection of suitable garden plants.
How do egg shells work as fertilizer?
Egg shells are made up of 90 to 95% calcium carbonate (CaCO3), also known as "calcium carbonate". Lime is useful for raising or stabilizing soil pH, but eggshells are slow to take effect. To dissolve the lime, carbonic acid (HCO3-) must be present in the soil, which is produced by the respiration of the plant roots. With the help of carbonic acid, the compound Ca(HCO3-)2 is formed, which in turn is converted into the calcium Ion Ca2+ , carbon and water rise - in this process the pH value increases. Unfortunately, this is not the case with clay-rich soils, as these are chemically too stable to be affected by the slowly acting addition of lime.
Tip: Heavy soils are better treated with quicklime or slaked lime if the pH needs to be raised. For example, quicklime is contained in untreated wood ash. You can read more detailed information on using wood ash as fertilizer in our special article. Always test the pH of your soil before applying lime.
The calcium ions released in the reaction with carbonic acid (Ca2+) are essential for cementing soil particles. They connect clay minerals to humus molecules and thus ensure stable crumbs that support plant growth in many wayssupport financially. And, of course, the released calcium is an essential nutrient element for plants: it serves to stabilize the cell wall and as a signal ion, which is involved in the opening of the stomata.
In addition to calcium, the nutrient elements potassium, phosphorus and magnesium are also contained in small amounts. Overall, the quantities of egg shells in the household are so small anyway that using them as fertilizer is only worthwhile in a few cases, as you will learn in the following paragraph.
Summary: How do eggshells work as fertilizer?
- Egg shells consist mainly of calcium carbonate
- Calcium carbonate can slowly raise soil pH
- The pH effect is limited to light, clay-poor soils
- Released calcium ions are valuable cements for soil particles and, together with humus and clay minerals, can improve the soil structure
- Calcium is one of the essential nutrients for plants
Because egg shells provide almost only calcium, it is not possible to fertilize with them alone. We therefore recommend an organic long-term fertilizer for the care of your plants: This promotes the build-up of humus molecules, which, in combination with Ca2+, become stable soil crumbs. Our Plantura organic fertilizers are such organic long-term fertilizers that even do without any animal components.
Application of eggshells as fertilizer
Egg shells are suitable for introducing calcium, raising the pH value and cementing soil particles. However, absolute calcium deficiencies and very low pH values are rare in German gardens; they occur, for example, on former moor areas. In peat-based potting soil, problems with calcium and the pH value can occur more frequently, because peat is very low in calcium. If large quantities of potting soil containing peat are introduced into the bed, a lack of lime can occur in the plants growing there over a long period of time. This is especially true in planters where volume is limited and there is no connection to the calcareous, natural soil. Of course, all lime-loving plants are particularly susceptible to this. In vegetable beds with lime-loving varieties and planters, the application of eggshells makes sense. On the other hand, distributing it over a large area on lawns or flower beds tends to have no effect, simply because of the small amount.
On light soilsand with beds improved with peat soil, you can apply about 100 to 200 grams of eggshells per square meter every three to four years - provided the pH is demonstrably too low. In any case, you should check this beforehand using a pH test so that the pH value is not influenced to levels that are harmful to plants. Basically, the effect of eggshells is greatly enhanced when they are finely ground. By increasing the surface area, the calcium carbonate dissolves faster. Incidentally, this depends on sufficient water being available for the solution, which is why it is advisable to apply it together with water.
Tip: Crush the eggshells in a mortar or pound them in a tea towel. You can then leave the resulting powder in a jug of rainwater for a day. When applying, however, you should make sure that you only wet the soil and not the plants - otherwise there will be unsightly lime stains. If possible, you should wear gloves when applying lime, as the high pH value damages the skin.
Please note: Calcium carbonate and also egg shells should never be distributed in connection with ammonium or phosphates. Therefore, keep a break of at least three months between the distribution of ammonium-containing fertilizers or phosphates and eggshells. When calcium and ammonium come into contact, gaseous, smelly ammonia is formed. Calcium and phosphate combine to form poorly soluble calcium phosphates, making both nutrients inaccessible to plants.
Egg shells on the compost heap
Another possible use of eggshells is to spread them on the compost heap. A high pH value stimulates the activity of bacterial soil dwellers and can thus accelerate composting. However, if the small composters are too active, the volume of the compost can be smaller. Egg shells should therefore only end up on the compost in connection with acidic material - such as rhododendron cuttings, ericaceous plants, peat soil, coniferous wood or oak leaves. A fine dusting of this material with ground eggshells is sufficient.
Summary: Application of Egg Shells as Fertilizer
- The calcium carbonate in egg shells can be used to increase the pH of acidic soils - these are quite rare in Germany though
- More oftenmay need to be applied to beds improved with peat soil or potted plants in peat based potting soil
- In any case, you should carry out a pH test of the soil before spreading
- Finely ground and mixed with water, the calcium carbonate of the egg shell works fastest
- You must never spread calcium carbonate in combination with ammonium or phosphates
- On the compost heap, eggshells can balance the low pH of acidic rotting material
Which plants can be fertilized with eggshells?
Lime-loving plants in beds and tubs will thank you for a supply of finely ground eggshells. The table below shows a selection of lime-loving garden plants. You can find some more lime-loving specimens in our article on fertilization with ash.
| Lime-loving shrubs | Calcite-loving vegetables | Lime-loving perennials |
|---|---|---|
| Roses (Pink) | All cabbage varieties (Brassica) | Columbine (Aquilegia) |
| Blackberries and raspberries (Rubus fruticosus/R. idaeus) | Carrots (Daucus carota subsp. sativus) | Crawling Bugle (Ajuga reptans) |
| Common Pear (Amelanchier ovalis) | Rhubarb (Rheum x hybridum) | Hazelroot (Asarum europaeum) |
| Barberries (Berberis) | Chicory Salad (Cichorium) | Asters (Aster) |
| Butterfly bush (Buddleja davidii) | Asparagus (Asparagus officinalis) | Blue Fescue (Festuca cinerea) |
| Boxwood (Buxus sempervirens) | Garlic (Allium sativum) | Grape hyacinth (Muscari botryoides) |
| Peonies (Paeonia i. S.) | Tomatoes (Solanom lycopersicum) | Lesser Snowdrop (Galanthus nivalis) |
| Currants (Ribes) | Onions (Allium cepa) | Cyclamen (Cyclamen) |
| Spiraen (Spiraea) | Celery (Apium graveolens) | Autumn Crocus (Colchicum autumnale) |
| Elder (Sambuccus) | Leek (Allium porrum var. porrum) | Star Globe and Giant Onion (Allium chrisophii,A. giganteum) |
| Fruit Trees | Beets (Beta vulgaris) | Sage (Salvia nemorosa) |
| And many more | And many more | And many more |
You can find more information about natural fertilizers in our special article.
Egg shells alone, however, cannot fully meet the nutritional needs of most plants. We therefore recommend that you also help with an organic long-term fertilizer. Our Plantura organic fertilizers naturally ensure strong and he althy plants over the long term and are therefore the ideal complement to fertilizing with eggshells.