Vinca Seedlings: Warmth, Light and Slow Early Growth

What to expect from a young plant

Vinca seedlings are slow, and this is where most people give up on them. Germination takes one to two weeks in real warmth, and then the seedlings sit for a fortnight looking as though nothing is happening while they build roots. Growth only becomes visibly quick once the plant has four or five leaf pairs and the temperature is holding steadily in the seventies Fahrenheit (low twenties Celsius).

That slow start is normal and is not a signal to intervene. The instinct to water more, feed, or move the tray somewhere warmer and darker is what kills seedlings at this stage. A tray of small, dark green, compact seedlings that has barely changed in ten days is exactly right.

Plan for around twelve to sixteen weeks from sowing to a plant fit to go outdoors. Anyone counting on six weeks will be caught out, and will either plant something far too small or plant it out too early into cold ground to make up the time.

Heat and light, in that order

Germination needs 75-80F (24-27C) and darkness, so cover the seed lightly with mix and keep the tray covered or in a dark warm place until shoots break through. A heat mat or the warmest room in the house makes far more difference than any other piece of equipment. Below about 70F (21C) germination is patchy and slow, and much of the seed simply rots.

The moment shoots appear, everything changes: uncover the tray and move it into the strongest light you have, and let the temperature settle to around 70F (21C). Seedlings left warm and dim for even a few days stretch into thin pale stems that never make sturdy plants. If you are using a windowsill, turn the tray daily so the seedlings do not lean.

Keep night temperatures up as well as day temperatures. A tray on a cold windowsill overnight can drop into the fifties Fahrenheit (low teens Celsius), which stalls growth and encourages the same rots that afflict plants set out early. Move trays back into the room at night if the glass gets cold.

Damping off and how to avoid it

Damping off is the one disease that reliably takes out vinca seedlings, and it comes from the same conditions that harm the adult plant: a wet surface, stagnant air and crowding. Affected seedlings topple at soil level with a pinched, darkened stem, and once it starts in a dense tray it moves through it within days.

Prevent it rather than treat it. Sow thinly enough that seedlings are not touching, use fresh clean mix rather than reused compost, water from below so the surface stays dry, and give the tray moving air once the seedlings are up, even if it is just an open door in the room. Remove the humidity cover as soon as germination is complete rather than leaving it on out of habit.

If it does appear, take out the affected seedlings and the mix immediately around them, stop watering until the surface is properly dry, and increase airflow. A tray caught early usually stabilizes; a tray left covered and wet usually does not.

Handle seedlings by a leaf, never by the stem. A crushed stem does not recover, and this plant has too few weeks to spare for a setback at this stage.

Potting up, pinching and hardening off

The hardening-off stage is where a good tray of seedlings can still be wasted. Plants raised at a steady 70F (21C) indoors have thin cuticles and scorch or check badly if taken straight into full sun and wind, so the gradual build-up genuinely matters even though the plant loves heat once it is adjusted.

Keep the young plants slightly hungry and slightly dry through this period rather than lush. A compact, hard-grown plant establishes far faster after planting than a large soft one, and it is much less likely to rot in the first fortnight.

1. Pot on at two or three leaf pairs Move each seedling into its own three-inch (8 cm) pot of free-draining compost, setting it at the same depth it was growing. Water once to settle it, then let the surface dry before the next watering. Keep the pots warm and in full light.
2. Feed only lightly Wait until the plant has been in its pot two or three weeks, then give a half-strength balanced liquid feed every two to three weeks. Heavy feeding at this stage produces soft floppy growth that transplants badly and is more prone to rot.
3. Pinch once for branching When the plant has four or five leaf pairs, take out the growing tip. It pauses for a couple of weeks and then breaks into several stems, which gives a denser plant and far more flowering points later. One pinch is enough.
4. Harden off over 7-10 days Stand plants outside in a sheltered spot on warm days and bring them in at night, extending the outdoor time gradually and building up to full sun. Skip cold or windy days entirely rather than pushing through them.
5. Hold them if the weather turns If nights drop back, keep the plants potted in a warm sheltered place instead of planting. Pot up into a larger container if roots fill the pot. A held plant loses nothing; a plant put into cold soil often loses the whole season.
6. Plant out into warm soil Plant only when night lows hold above 55-60F (13-16C) and soil at planting depth is above 65F (18C), spacing 10-12 inches (25-30 cm) apart. Water lightly for the first two or three weeks, then let the plants take over.

Records worth keeping at this stage

Note the sowing date, the date the first seedlings emerged, and the date the plants were finally big enough to go out. Those three points give you the real length of your raising period, and if it came out longer than you expected, next year's sowing simply moves earlier by that difference.

Also record the germination rate roughly, and the temperature you actually achieved rather than the one you intended. Poor germination in this plant is nearly always a temperature story, and having the number written down turns a vague sense that it went badly into a fix you can apply.

Keep seed, seedlings and prunings out of reach of children and pets, and wash your hands after handling them. Every part of this plant is poisonous if eaten and the sap can irritate skin.