How to Stop Thyme Going Woody and Dying Out in the Middle

Why the middle goes bare

Thyme is a sub-shrub. Every stem it grows this year becomes bark next year, and bark does not carry buds. So the living, leafy part of the plant creeps outwards a couple of inches a season while the center behind it turns to bare gray wood. By the third summer an unclipped plant is a ring of green around a dead middle, and no amount of feeding or watering brings the center back.

The cause is not age or disease. It is simply that nobody cut it. A stem clipped while it is still green and soft pushes new shoots from just below the cut, and those shoots keep the base of the plant furnished. A stem left to run flowers at the tip, hardens all the way down, and is finished as a source of new growth.

Record the year you planted or last replaced each thyme. A plant is usually worth renewing at four or five years, and without the date written down nobody ever remembers which one is oldest.

Cut it twice a year while it is still green

Two clips a year keep a plant dense for years. The first is a light shortening in spring as growth restarts; the second is a hard cut straight after flowering, in the second half of summer. The rule that matters more than timing is where you cut: never below the green.

Look down a stem from the tip. There is soft green growth, then a section carrying small leaves, then bare gray wood. Cut anywhere in the green and it shoots. Cut into the gray and that stem is dead, permanently. Because thyme stems are thin, judge this stem by stem rather than running shears blindly across the top.

1. Spring: take the tips off As new growth starts, shorten every shoot by an inch or two (3 to 5 cm). This is not for the harvest, it is to make each shoot fork into two. Feel free to take winter-damaged, blackened tips right back to green at the same time.
2. After flowering: cut by a third Once the flowers have faded, cut the whole plant back by about a third, staying in leafy growth. This is the cut that keeps the center furnished, and it is the one people skip.
3. Leave two pairs of leaves On each stem, leave at least two pairs of leaves below your cut. The buds in those leaf joints are what produce the new shoots. A stem cut bare will not reshoot.
4. Stop cutting six weeks before frost Late cuts push soft shoots that have no time to harden, and those are the shoots that blacken and rot over winter. Once nights start dropping, leave the plant alone.

Never shear a woody plant back to a stump hoping it will regrow. Thyme has almost no dormant buds in old wood. If the green is gone, the plant does not come back.

Winter wet kills far more thyme than winter cold

Common thyme is hardy to well below 0F (-18C) in a dry soil, and dies at 25F (-4C) in a wet one. Almost every thyme lost over winter was drowned rather than frozen. The roots are fine and shallow, they need air, and a soil that stays saturated for weeks rots them from below while the top still looks alive.

The tell is a plant that greens up in early spring and then collapses gray and crisp in a fortnight, often with the whole rootball lifting away in your hand. By then it is too late. The work has to be done at planting, by raising the plant above the wet.

1. Plant high Set the crown an inch (2 to 3 cm) proud of the surrounding soil, never in a dip. Water should run away from the stem, not collect at it.
2. Open up heavy soil On clay, work in coarse grit at roughly a third by volume to a spade's depth, or build a raised bed or mound six inches (15 cm) high. Compost alone does not fix clay for thyme; it holds more water.
3. Mulch with grit, not bark Spread a half inch (1 cm) of grit or gravel around the crown. It keeps the lower foliage off wet soil and stops rain splashing soil into the plant. Bark and straw hold moisture against the stem and make the problem worse.
4. Tilt containers in winter Stand pots on feet, or tip them slightly, so they drain freely. A pot standing in its own saucer through a wet winter will kill thyme reliably.

In a pot, use a free-draining mix: about two parts all-purpose potting mix to one part coarse grit or perlite. A rich, water-retentive compost gives lush growth with weak scent and a plant that will not see spring.

Water and feed less than feels right

Thyme comes from thin, dry, stony Mediterranean ground and its flavor comes from being slightly stressed. Watered and fed like a vegetable it makes long soft shoots, pale leaves and noticeably weaker scent, and it goes woody faster because that soft growth hardens badly.

In open ground an established plant needs no watering at all except in a long drought. In a container, water only when the compost is dry an inch (2 to 3 cm) down, and then water thoroughly and let it dry again. Feeding is rarely needed: a single light dressing of a low-nitrogen general fertilizer in spring is plenty, and in the ground even that is optional.

Soft, floppy shoots with big pale leaves and little smell mean too much nitrogen or too much water. Cut them off, stop feeding, and the next growth comes back tighter and more aromatic.

Sun and air matter more than soil quality

Thyme wants at least six hours of direct sun and moving air around it. In shade the shoots stretch, the leaves thin out, the plant sprawls open and the center bares itself far earlier. Crowded against other plants or a wall the foliage stays damp after rain and gray mold takes hold at the base.

Poor, thin soil is not a problem at all. A gritty, alkaline-to-neutral soil that nothing else wants suits thyme better than a well-manured bed. The one thing it will not tolerate is shade combined with damp.

1. Give each plant a foot of space Set plants 12 inches (30 cm) apart. Closer than that and neighboring plants shade each other's bases, which is exactly where you want green growth.
2. Keep it off walls and edging Leave a hand's width between the plant and any solid surface. Air needs to pass through the plant, not stop at it.
3. Lift the skirt in autumn Trim off any shoots lying flat on soil or mulch. Those are the ones that rot first and take the crown with them.

A container is often the better answer on wet clay. A 10 inch (25 cm) pot of gritty potting mix in full sun, up on feet, will outlive the same plant in a border by years.