Gadenin日本語Get the appAim for dormant, not green
The instinct with a tender plant is to bring it into the warmest room in the house and keep it growing. With lemon verbena that instinct is exactly wrong, and it is the single most common reason plants are lost over the cold months. Warm air, short dark days and dry indoor heating give you long weak drawn shoots, leaves that fall anyway, and a red spider mite infestation by the time spring arrives.
This plant is deciduous. It is built to lose its leaves and rest, and it comes back better for having done so. The target is a plant that stands bare, cool and nearly dry for the whole cold season and then breaks bud strongly when warmth returns. A bare verbena is not a failed verbena; it is a verbena being overwintered correctly.
So do not fight the leaf drop. When nights cool and the leaves yellow, take the harvest, let the rest fall, and move the plant into its rest. What it needs from you after that is shelter from frost and restraint with the watering can, and very little else.
| Overwintering spot | Suits it? | Notes |
|---|---|---|
| Unheated garage or shed with a window | Ideal | Cool, frost-free, dim light is fine once bare |
| Cool spare room or porch | Very good | Keep it well away from radiators |
| Frost-free greenhouse | Very good | Watch for cold snaps; wrap the pot if needed |
| Warm living room | Poor | Drawn growth, leaf drop anyway, spider mite |
| Left outdoors in a pot in a cold area | Risky | The root ball freezes through; only viable in mild areas with heavy protection |
How cold it will take
An established plant in open ground in a mild area, with the crown mulched deeply, will come through short spells around 20F (minus 7C) and reshoot from the base even if all top growth is killed. That is the best case and it depends on well-drained soil; cold plus wet kills it where cold alone would not.
A plant in a pot is far less hardy than the same plant in the ground, because the root ball freezes right through where soil-insulated roots would not. Treat a container plant as needing genuine frost protection rather than a sheltered corner. Somewhere that stays between roughly 35F and 50F (2C and 10C) is close to perfect: cold enough to hold it properly dormant, warm enough that the roots never freeze.
The other half of hardiness is preparation. A plant that was still being fed and still pushing soft growth when the cold arrived is much more likely to suffer than one that stopped feeding as summer ended and had time to ripen its wood. Stopping the feed on time is part of overwintering, and it happens weeks before you move the pot.
- Stop feeding as the season cools Late nitrogen produces soft growth that cannot harden. Stopping in good time lets the wood ripen, which is what actually carries the plant through cold.
- Take the main harvest before the first cold nights The leaves will drop within days of the first real chill. Cut and dry everything worth having rather than losing it to the ground.
- Move it under cover early Bring the pot in before the first frost rather than after. Waiting costs you nothing in fragrance and risks root damage you cannot see.
- Cut watering right back A bare dormant plant uses almost nothing. A splash every three or four weeks, enough that the root ball is never dust-dry, is the whole regime.
- Leave the pruning until spring Cut stems die back from every wound over the cold months. Cutting in spring, once buds are visible, means you keep the wood that survived.
Through the dormant months
Once the plant is bare and in its resting place there is almost nothing to do, and doing nothing is the skill. No feeding at all. No pruning. No moving it back and forth to somewhere warmer on mild days, which just triggers premature growth that then gets cold-damaged.
Check it every few weeks. Feel the weight of the pot and give it a small drink only if it feels alarmingly light; the aim is a root ball that is dry to the touch on top but not powdery through. Look for mold on the compost surface, which means it is too wet and too still, and improve the airflow if you see it. Scratch a stem occasionally if you want reassurance that the wood is still green.
If the pot is somewhere that could dip below freezing, wrap the pot rather than the plant. Bubble wrap, row cover or hessian around the container insulates the roots, which is what actually matters on a leafless plant. Standing the pot on feet or a block of wood keeps it off cold concrete, which conducts heat out of the compost surprisingly fast.
Do not stand a dormant plant near a radiator or in a heated conservatory that swings from hot afternoons to cold nights. Steady cool is far better than warm and variable. Fluctuating warmth repeatedly wakes the plant and exhausts it before spring.
Bringing it out of dormancy
Lemon verbena wakes late, and every year people give up on a plant that was about to break bud. Do not judge it until the weather has been genuinely warm for a few weeks. Buds appear along the older wood rather than at the tips, so look down the stems rather than at the top.
As days lengthen and temperatures rise, move the plant somewhere brighter and warmer and start watering a little more, but only a little until leaves appear. A plant with no leaves still cannot use much water, and this transitional period is when overwatering does its damage.
Once buds are visibly swelling, do the hard spring cutback and repot or top-dress in the same session. Then hold it under cover until frosts have finished, harden it off over a week, and move it outside into full sun. From there the growing season takes over and the plant is away.
If a plant is bare and the wood is brittle and brown right down, check the base before giving up. Lemon verbena frequently reshoots from the crown at soil level even when every stem above is dead. Keep the pot barely moist and warm for another month before discarding it; plenty of apparently dead verbenas throw shoots from the base weeks after everything above ground has been cut away.
Recording what got it through
Overwintering is where notes earn their keep, because you only get one attempt a year and the variables are easy to forget.
Record where the plant overwintered, and if you can, the coldest temperature that spot reached, so you can judge whether it was cold enough to hold dormancy or cold enough to do harm. Record the date it lost the last of its leaves and the date the first bud broke, which is the measurement that stops you panicking next year. Record how often you watered through the dormant months and how the compost felt, and pair that with whether any roots or stems rotted. Record the date you stopped feeding and whether soft growth was still present when the cold came. If you overwinter more than one plant in different places, note which spot each one was in and how each looked in spring, because one season of that comparison settles the question of where they go from then on.