Gadenin日本語Get the appThe shape of the verbena year
Unlike an evergreen herb that ticks along all year, lemon verbena has four distinct phases and the transitions between them are what you actually manage. It sleeps bare and dry through the cold season, wakes late and slowly, grows explosively through the warm months, and then shuts down over a couple of weeks as nights cool. Get the timing of the two transitions right and the rest looks after itself.
Nothing in this cycle runs on the calendar. It runs on temperature and on frost, so the same plant in two different gardens can be four to six weeks apart. The triggers to watch are the last frost, night temperatures holding above about 50F (10C), and the first cold nights of autumn.
The one thing that stays constant is that lemon verbena wakes later than you expect and shuts down earlier than you expect. Plan for a shorter growing season than the herbs around it, and take your main harvest before the weather makes the decision for you.
| Phase | Trigger | Main jobs |
|---|---|---|
| Dormant | After leaf drop until buds swell | Keep cool, frost-free and nearly dry; no feed, no cutting |
| Waking | Nights above 50F (10C), buds swelling | Hard cutback, repot or top-dress, start watering, move to light |
| Full growth | After the last frost, warm days | Feed fortnightly, water hard, pinch and cut regularly |
| Winding down | Nights cooling, growth slowing | Stop feeding, stop pinching, take the main harvest |
| Leaf drop | First cold nights | Move to shelter, cut watering right back, let it go bare |
Spring: cut hard, then wait
The single most important job of the year is the spring cutback, and the reason is that this is a shrub. Left uncut it extends the same few stems further and further, so all the leaves end up out of reach at the tips and the base goes bare and woody. Cutting hard forces new shoots low down and that is what gives you a leafy, pickable plant.
Wait until you can see buds swelling on the old wood before you cut, so that you are cutting to live growth rather than guessing. Then take the framework down by about half, or harder on an old leggy plant, always cutting just above a visible bud or leaf pair. Remove anything that snaps dry and brown at the same time.
Repot or top-dress at the same session. A plant coming out of dormancy has an almost empty root system and a fortnight of settling in ahead of it, so this is by far the least disruptive moment of the year to disturb the roots. Then start watering again, lightly at first and building up as the leaves come, and be patient. Buds break slowly and the plant may sit apparently unchanged for two or three weeks before anything obvious happens.
- Wait for swelling buds before cutting Cutting a fully dormant plant means guessing where the live wood ends. Waiting a few weeks until buds are visible makes the whole job obvious and safe.
- Take the framework down by half Cut each main stem back to a strong bud or leaf pair, roughly halving the plant's height. On an old plant with bare lower wood, cut harder still.
- Repot or refresh the compost Move up one pot size, or tip it out, trim an inch (2.5 cm) off the root ball all round and return it with fresh free-draining mix.
- Restart watering gradually Water lightly at first. A bare plant with no leaves loses very little water, and a soaked pot at this stage rots the roots you need.
- Move outside only after the last frost New spring growth is soft and a late frost will blacken it. Harden the plant off over a week once frosts have finished.
Summer: the productive months
Once nights are reliably warm the plant grows fast, and this is when you take almost everything you will use. Feed a balanced liquid feed every two weeks, water thoroughly whenever the top two inches (5 cm) are dry, and keep the plant in the sunniest position you have. Full sun gives the strongest oils and the most compact growth.
Cut and pinch continuously. Every stem tip you remove becomes two shoots, and a plant harvested every three or four weeks through the warm season stays dense and gives far more than one picked at occasionally. Take up to a third of the plant at a time and let it come back.
Small pale sprays of flowers appear on some plants in high summer. They are pleasantly scented but they divert energy away from leaf production, so pinch them out as they form unless you want to enjoy them. This is also the season when red spider mite appears on plants under cover, so check the undersides of leaves whenever you pick.
The end of the season and the dormant rest
As days shorten and nights cool, stop feeding and stop pinching. Both push soft growth that cannot harden in time, and soft growth is what fails first when the cold arrives. Let the plant slow down and firm up its wood.
Take the main harvest before the first cold nights rather than after. Once the plant is triggered into dormancy the leaves yellow and drop within days, and a season's worth of fragrant leaves ends up on the ground. Cut everything worth having and dry it.
Then let it go bare without panic. Move the pot somewhere cool, bright enough but frost-free, and cut watering to a splash every three or four weeks. Do not feed, do not cut it back at this stage, and do not try to keep it in leaf in a warm room. It wants to sleep, and a plant that gets a proper cold, dry, dormant rest comes back stronger and later problems with pests are far less likely.
Do not do the hard cutback in autumn. Cut stems die back a little from every wound over the dormant months, and cutting before that dieback means the plant loses the wood you wanted to keep. Tidy in autumn if you must, and cut properly in spring when you can see live buds.
The dates that make next year easier
Because everything in the verbena year runs on temperature rather than the calendar, and because the plant spends months looking dead, a written record of your own conditions is more useful here than with almost any other herb.
Record the date of the last leaf fall and the date the first bud broke, and after two years you know your plant's dormant window precisely enough to stop worrying about it. Record the date and depth of the spring cutback next to how fast the plant filled out, so you can adjust how hard you cut. Record every harvest date and the regrowth time between them, which tells you how many cuts your season really supports. Record the date you stopped feeding and the date of the first cold night, since the gap between the two is the margin you have to get the main harvest in. Record which position the pot stood in over the warm months and where it overwintered, along with whether it came through cleanly, because the overwintering spot is the variable that most often decides whether you have a plant at all next spring.