Lemon Thyme

Once the ground has frozen in midwinter, lay a loose mulch over the planting. Water about once a month during dry winter spells. Wait for a frozen surface rather than mulching in fall. Repeated freeze and thaw lifts these shallow, wiry root systems clear out of the soil and tears the roots. The mulch is there to hold the ground frozen, not to keep it warm, which is why it goes on after the freeze rather than before.

Skip the routine feeding. Lemon thyme does well in poor, coarse, gritty soil, and needs no more than a thin spring topdressing of compost on a truly depleted bed. Put the effort into drainage instead. Heavy nitrogen drives weak, tall, watery growth at the expense of the aromatic oil you are growing the plant for, and that soft growth sits wet and invites root rot and fungal trouble.

In spring, lift the whole root ball of an established plant and pull or cut it into smaller pieces, keeping rootlets attached to every piece. Replant at the original depth, 8 to 12 inches apart. Lemon thyme also comes readily from four-inch cuttings of shoot tips struck in sand. Division is how you renew the planting before the parent goes woody, and it is the reliable route for lemon thyme in particular, which does not come true from seed the way common thyme does.

Every few years, when the clump has gone gray and twiggy with leaves only at the tips, cut it back severely in spring as growth resumes. If a plant no longer answers a hard cut with new shoots, replace it from cuttings or a division. Lemon thyme is a subshrub that lays down wood from the base outward every year. Old wood carries no leaf buds, so without periodic renewal the productive green shell moves further out and the plant slowly hollows.

When the first flower buds appear but have not yet opened, cut the leafy branch tips back by two to three inches. Gather on a dry day after the dew has burned off and before midday. You can keep snipping tips all season, but this is the cut worth drying. Essential oil in the leaves peaks just before the plant flowers and then drops as the plant puts its energy into bloom, so the same leaves cut a few weeks later carry noticeably less lemon.

After the pink-lilac flowers brown off, shear the spent bloom and the top third of the growth away. Do not cut into the bare woody base, which will not resprout. Trimming after bloom pushes a flush of young tender stems instead of letting the plant set seed and harden off, and it slows the drift toward all-wood, no-leaf growth.