If you are growing calendula on your small farm, you're probably planning to sell it one of a few ways: dried for others to make products like salves, oils, and teas with; or processed into any of those products. Perhaps you want to make a calendula-plantain-chickweed salve for skin conditions or put flower petals in your goat's milk soap. Whatever your value-added product, you will want to harvest and dry the calendula first. Here's how to do it.
The best time to harvest calendula flowers is in the morning after the dew has dried. They are fresh, opening to the sun, but don't have wet petals. You should also harvest the blossoms when they are half-open. Soon after this point they open more and are past their prime medicinally, and the petals begin to wither.
Snipping off the flower head at the top of the stalk is the standard way to harvest calendula. Use scissors or your fingers to pinch the stem. You could also pull entire plants and include the leaves, which have much of the same medicinal quality as the flowers, but it's so much easier to continually harvest flower blooms from a patch of calendula throughout the season.
You may want to trim back the stem that remains on the plant so that the stem does not begin to rot.
With calendula, the more often you harvest, the better. If you allow blossoms to stay on the plants, they will go to seed. When you deadhead frequently, the blooms will return and multiply. So snip early and snip often!
How to Dry
There are many ways to properly dry flowers for medicinal use. The basic idea is to provide air circulation as well as protection from too much sun (if outdoors, dry in a shady area). Don't wash the flower heads. Spread them onto a ventilated surface: cloth, screen, a mesh of some type. You can build drying screens from light lumber and screen―make a frame and staple screen to it. You can even build a cabinet to hold the screens and put a fan in it to circulate air.
Farmers who harvest herbs on a larger scale use hoop houses to dry them. Cover the hoop house with shade cloth and lay the screens along with an open bench on the sides, or hang mesh bags with multiple mesh drying layers from the supports.
You can also use an electric dehydrator indoors to dry the calendula. Use a temperature of 90 to 95 F. You don't want to expose the delicate flowers to too much direct heat.
Storage and Uses
Before storing calendula, make sure it is completely dry. The green flower heads are dense and take much longer to dry than the petals. The petals will feel wispy and fragile when they are completely dry, and they will pull out of the heads extremely easily.
You can store calendula flowers whole with the green flower head, or pull the petals out and compost the heads. For tea or tincture purposes, you may wish to provide just petals to your customers. If you're making oil, you may find it easier to use the whole head, avoiding the labor of plucking the petals.
Store dried calendula in glass jars with airtight seals or sealed plastic bags or under vacuum seal. Keep it out of the light.
Once dried, you may use calendula blossoms to make oil, which can then be used to make a salve.
Calendula Officinalis. North Carolina Extension Gardener Plant Toolbox
Marrone, Teresa. The Beginner's Guide to Making and Using Dried Foods: Preserve Fresh Fruits, Vegatables, Herbs, and Meat with a Dehydrator, a Kitchen over, or the Sun. Storey Publishing, 2014