Gadenin日本語Get the appWhat the seed needs
Lemon balm seed is very fine and it needs light to germinate. That single fact accounts for most failures: sown at the depth people habitually use for herbs, it simply never comes up. It goes on the surface of the compost, pressed down into contact, and covered with nothing at all, or at most the thinnest dusting of vermiculite that you can still see light through.
It also wants steady warmth and patience. Germination takes ten days to three weeks and is uneven, so seedlings keep appearing after you have decided the tray has failed. Do not throw a tray away for a month.
| Requirement | What it needs | What happens if you get it wrong |
|---|---|---|
| Sowing depth | On the surface, pressed down, uncovered | Buried seed does not germinate at all |
| Temperature | Steady 65 to 70F (18 to 21C) | Below 60F (15C) it is very slow and patchy |
| Light | Bright light on the surface from the day you sow | In the dark it will not start |
| Moisture | Constantly damp, never wet | Fine seed on a surface that dries once will not recover |
| Time | Ten to twenty-one days, uneven | Trays are often discarded a week too early |
Water surface-sown trays from below by standing them in a shallow dish, or with a fine mist. A watering can will wash the seed into a corner and you will get all your seedlings in one clump.
Sowing in trays
Starting under cover gives far better results than sowing where the plants are to grow, because you can control the moisture on the surface and the seedlings are not competing with weeds while they are tiny.
- Fill and firm Use a fine seed-starting mix in a shallow tray or small pots. Fill, tap down, and firm the surface flat. A rough surface swallows fine seed into the crevices, which buries it.
- Water first, then sow Wet the compost thoroughly and let it drain before the seed goes on. Sowing onto damp compost means you do not have to water over the top of the seed afterwards.
- Sow thinly on the surface Scatter the seed as thinly as you can manage and press it lightly into the surface with a flat hand or a piece of board. Do not cover it.
- Cover the tray, not the seed A sheet of clear plastic or a propagator lid holds the surface moisture without excluding light. Keep it somewhere bright at around 65 to 70F (18 to 21C) and take the cover off as soon as the first seedlings appear.
The slow first month
Lemon balm seedlings are unpromising to look at. The first pair of true leaves are small and rounded, and for three or four weeks the plants sit there apparently doing nothing while they build roots. This is normal and is not a sign that they need feeding or more water.
The dangers in that period are damping off and drying out, and both come from the same handling. Keep the surface damp but never sodden, give them all the light you have, and get some air moving over the tray once the cover is off. A crowded tray in still humid air is the one that collapses overnight.
Once they have three or four pairs of leaves they change gear and grow fast.
Transplanting seedlings and potting up
Move them into individual small pots when they have their first two pairs of true leaves. Lift each seedling by a leaf, never by the stem, using something thin to ease the roots out, and plant it at the same depth it was growing.
Grow them on in good light. When roots show at the drainage holes, shift them into a pot around four inches (10 cm) across; a seedling held too long in a plug goes hard and stalls, and a stalled lemon balm seedling is slow to pick up afterwards.
Pinch out the growing tip once a plant has four or five pairs of leaves. It branches from the joints below and you get a bushy plant instead of a single tall stem that flops when you put it out.
Hardening off and planting out
Plants raised in warmth need a week or so outdoors in the day and under cover at night before they go into the ground. Skipping that check gives you scorched, bleached leaves for a fortnight even though the plant survives.
Plant out after the last frost, when the soil has warmed, spacing them about eighteen inches (45 cm) apart. That looks absurdly generous around a small seedling and it is exactly right by the end of the season, because each plant makes a clump two feet (60 cm) across. Water them in well and keep them watered through the first summer while the roots go down.
Expect a light picking in the first season and a full one from the second year. Do not cut a first-year plant hard; take a third at most.
Volunteer seedlings, and what to record
Once you have a flowering clump the garden will sow lemon balm for you, usually more generously than you want. Seedlings appear around the parent in spring and sometimes several feet away. Lift the ones you want while they are two or three inches (5 to 8 cm) high and hoe off the rest before they make a taproot and become a real job.
Seedlings are not identical to the parent. Rub a leaf between your fingers before you decide to keep one: the scent varies noticeably from plant to plant, and some are distinctly weak. Keeping the best-smelling volunteers and discarding the rest quietly improves the lemon balm in your garden over a few years.
Two things are worth writing down at this stage: the date you sowed against the date the first seedlings actually showed, and where in the garden the volunteers came up each spring. The first tells you whether your propagator is warm enough to be worth using; the second tells you whether you are cutting the parent clump early enough.