Whether you grow herbs in your kitchen or outside in the garden, sooner or later they are going to need fertilizing. However, if you happen to be growing herbs with woody stems — such as rosemary (Salvia rosmarinus), lavender (Lavandula angustifolia), and thyme (Thymus vulgaris) — you can skip the fancy store-bought fertilizers and just use your kitchen scraps from breakfast. Eggshells are a great source of calcium carbonate, but also contain smaller amounts of other important nutrients such as iron, magnesium, manganese, phosphorus, potassium, and zinc. 

Because of the calcium content, eggshells can act as a cheap, easy replacement for lime in your garden, especially for plants that don’t need many other nutrients. Woody herbs, many of which tend to be sun-loving Mediterranean herbs, thrive in poor, dry soil. In other words, they don’t want to be over-fertilized. In fact, if you do give these plants too much fertilizer, you may impact the way they smell and taste. Generally, these plants only really need fertilizing once per year, if at all. Calcium helps plants develop strong, healthy roots and shoots, build stronger cell walls, and generally be more healthy. So, if you want to give your woody herbs a boost, calcium-rich eggshells are a simple effective way to give them some nutrients without overdoing it.

Eggshells have many unexpected uses around your home and garden, but if you’ve ever put them into your compost bin, you may have noticed they don’t break down quickly. Because of this, simply tossing your eggshells into the soil probably won’t do much good in the short term. Before you begin, rinse the eggshells and microwave them for about two minutes to kill any potential pathogens lurking within.

Some gardeners like to use a blender, food processor, or even a coffee grinder to break the shells up into a fine powder. You can crush the eggs by hand as well, but using your kitchen gadgets will speed up the process and likely result in a finer powder. However, calcium carbonate is not always easily bioavailable to plants and is not a quick fix in this form. That shouldn’t be a problem, as your woody herbs aren’t likely to be starved for nutrients. Still, plants can only take up minerals when they are dissolved in water, so simply soaking shells in water for a few days before using that water to give your plants a drink may be a simpler, quicker way to get calcium to your plants. You can also sprinkle this leftover kitchen scrap around your hydrangeas or other plants in your garden. Just be careful not to overdo it and cause an imbalance.