Compost is simply the best way to improve your garden, and making your own compost is an engaging garden activity for kids. Turning a compost pile is a much-enjoyed hands-on activity, and it provides an excellent opportunity to teach kids about the nutrient cycle and the importance of environmentally sustainable practices. Compost offers many benefits to soil, and to the plants growing in it. Compost adds nutrients and organic matter, improves soil drainage and water-holding capacity, nurtures the soil ecosystem, and so much more.
If you're sold on the benefits of compost but are lacking in materials to add to your bin, consider growing a compost garden. As odd as it may sound, the idea of growing plants specifically to add to compost pile has been around a long time. It's a favorite technique used by advocates of permaculture (“permanent agriculture”), who know that healthy soil is the foundation for healthy, long-lived, and productive plants.
The idea is simple: Grow plants, cut off the tops, and add them as “green material” to your compost bin. This technique is especially helpful if you have loads of “brown” materials, such as dried leaves, but lack sufficient “greens” (food scraps, fresh grass clippings, just-pulled plants). Nitrogen-rich green materials are critical to keep the compost cooking. (Learn more about composting.) You can grow a whole garden of compost plants, or tuck plants here and there into empty spots or areas left open when crops are harvested.
What characteristics should you look for in a compost plant? Let’s look at borage (Borago officinalis), one of the best plants to grow in a compost garden. Borage:
- Germinates easily and grows quickly.
- Produces lots of above-ground biomass (a fancy way of describing a large volume of stems and foliage).
- Takes up many nutrients, notably zinc and potassium, gathering and storing them in its foliage until they’re released into the compost during decomposition.
- Is an attractive plant with fuzzy, nodding buds that open to pretty blue, pollinator-friendly flowers.
Borage (pronounced BORE-edge) has been used as a medicinal plant for centuries, if not longer. (The species name “officinalis” often denotes a plant with medicinal properties.) The leaves can be used to make a delicate, cucumber-flavored tea and the star-shaped flowers brighten a salad.
A warm-season annual, borage grows best in full sun to light shade with well-drained soil. Sow seeds after your average last frost date, planting them 1/4" to 1/2" deep. Once the seedlings are up and growing well, thin them to leave about one plant per square foot. Keep the soil moist but not saturated.
Although individual plants die back each year, the plant is famous for its tendency to self-sow — that is, to drop seeds that will germinate the following season, effectively creating a permanent stand. The seedlings are easy to pull when they’re small, but if you’re concerned about the plant taking over, prune off the flowers as they develop.
Off to the Compost Pile!
You can add borage trimmings to your compost any time. Ideally, you’ll alternate a layer of freshly cut stems with some dry, brown materials to help compost microbes thrive. Depending on the length of your growing season, you may be able to harvest the plant every month or so, cutting it back by 1/3 to 1/2 each time. Chopping the plant (with pruners or a mower) creates small pieces that will decompose more quickly than larger ones. Then, as the first fall frost approaches, cut off the plant at the soil line, prune away the thickest stems, and cut the rest into pieces as the final gift to your compost pile.
Other Compost Garden Plants
Comfrey. Permaculture afficionados often grow comfrey (Symphytum officinale) to add to their compost. The plants form very deep roots that “mine” nutrients from the depths of the soil and incorporate them in their huge leaves. The downside to those deep roots is that comfrey can become invasive. It’s impossible to pull out the entire plant by its roots, and every root piece you leave behind becomes a new comfrey plant. If you choose to grow comfrey, know that you’ll have it in your garden for many years. This fast-growing Russian native will tolerate temperatures down to -40 degrees F. and is rated for hardiness zones 3-9. (Comfrey fans will tell you that it will grow just about anywhere.) The plant can be grown in large containers to keep it in bounds, though the roots won’t be able to mine soil nutrients as effectively when they’re confined to a pot.
Legumes. The most obvious reason to grow legumes, such as clover, alfalfa, peas, and beans, to add to your compost is for the nitrogen. Legumes form a symbiotic (mutually beneficial) relationship with soil bacteria, which create nitrogen-rich nodules on the roots. When you pull up the plants, roots and all, and add them to your compost, it benefits from this added nitrogen. You can also shear the plants back during the growing season and add the trimmings to the pile.
Yarrow. Accumulating a variety of nutrients in its leaves, including sulfur, copper, and potassium, yarrow (Achillea millefolium) is a useful compost garden plant. Some people are convinced that it speeds up the composting process, too. Yarrow is hardy, drought-tolerant, adaptable, and forms flat-topped flower clusters that are magnets for pollinators. There one downside: Yarrow is so adaptable, it can spread and become invasive and weedy.