Complete Your Gardening Cycle: Growing Seeds

In my garden, most of the annual herbs such as borage and love-in-a-mist reseed themselves without any intervention on my part. Many of the herbaceous (nonwoody) perennial herbs also tend to reseed with reckless abandon. I’m sure anyone who has grown lemon balm, feverfew, chives, elecampane, pennyroyal, fennel, or sweet violets knows only too well the multitudes of seedlings these plants can generate and the area they can claim as their own. The only reason I might collect seeds from such plants would be to give them away or to control their rampant spread. The woody perennial herbs such as lavender, rosemary, and the thymes are more restrained in self-seeding and produce far fewer offspring. I normally propagate these herbs vegetatively rather than by seed, however.

Some herbs don’t self-sow freely, some cast their seed far from the parent plant (even, like butterfly weed and dandelion, on the wind), and some are difficult to propagate by cuttings or root division. It is from these groups that I collect seed for propagation in later seasons.

General Harvest Methods

In late summer, I begin checking the garden for signs of seed development. The withering or dropping of flowers indicates that seeds have begun to form. After that milestone, I watch for flower stalks that have dried and turned brown and seedpods that have turned from green or yellowish brown to brown, gray, or black. The vast majority of herb seeds are brown or black when ready to harvest.

A reliable test of seed maturity is a light tap on the dry flower stalk. If any seeds rattle or are dislodged, they are ready for harvest. Also, watch for birds eating the seed heads (as they do reliably on my Agastache plants). This is an obvious indication not only that the seed may be mature (though some birds will eat green seeds) but that you’d better get out there and harvest it. If the seeds are small or contained in pods so that their maturity isn’t outwardly visible, as in the sages (Salvia spp.) or anise hyssop (Agastache foeniculum), I select a dry, brown flower stalk and remove some of its seeds; if they’re dark brown or black, it’s time to harvest them.

I harvest seeds late in the day after a few days of dry weather to ensure that all plant parts are dry. If the foliage or seed head is wet when picked, it will not dry quickly and is likely to mold. Few sights are more disappointing than a bag of seed heads that have turned to compost.

Cut the entire seed head or part of the flower stalk that contains seeds, avoiding any part of the plant that is still green, and place it in a large paper bag, cardboard box, or wooden bowl. Place only one kind of seed in each container, and label each with the name of the herb it contains.

Occasionally, I come across seed heads that are covered with aphids. I harvest them anyway but then place them in the freezer for a few days to kill the aphids. This doesn’t seem to harm the viability of the seed.