Gadenin日本語Get the appWhat the seed needs
Portulaca seed is tiny, roughly the size of ground pepper and dark gray to black. It germinates on light, which means it must sit on the surface of the compost and must not be covered with soil, vermiculite or anything else. Sprinkling even a thin layer over the top is the most common reason a tray fails to come up, and it looks like poor seed rather than a technique error.
Warmth is the other requirement. The seed wants a steady 70 to 75F (21 to 24C) and germinates in seven to fourteen days at that temperature. Below about 60F (16C) it may sit for weeks and then rot. There is no benefit in soaking, chilling or any other pre-treatment; the seed is straightforward if it is warm and lit.
Because the seed is so fine it is almost impossible to sow thinly enough by hand. Mixing a pinch of seed into a tablespoon of dry sand and scattering the mixture spreads it far more evenly and lets you see where it has landed. Sowing too thickly gives a dense mat of seedlings that is difficult to transplant and prone to damping off.
Do not cover the seed. Water from below by standing the tray in shallow water until the surface darkens, because watering from above washes surface-sown seed into corners and buries it.
Sowing indoors for an early start
Sow six to eight weeks before your last expected frost if you want flowering plants as early as possible. Use a shallow tray or small pots filled with a free-draining mix of about half seed-starting mix and half grit, sand or perlite, firmed level and watered from below before the seed goes on. A gritty surface also reduces damping off, which is the main risk with a tray of succulent seedlings.
Light matters as much as heat at this stage. A warm windowsill with weak light produces thin, pale, stretched seedlings that never make good plants. If your brightest position is not very bright, sow later rather than earlier; a plant sown two weeks after another in better light will overtake it and be sturdier.
Keep the surface just barely damp until germination, then reduce watering sharply. From the moment the seedlings appear, the risk shifts from drying out to rotting, and these plants tolerate dryness far better than they tolerate a wet surface.
- Fill a shallow tray with gritty mix and level it Use roughly half seed-starting mix and half grit, sand or perlite. Fill to about half an inch (1 cm) below the rim, firm gently with a flat board so the surface is even, and water it from below until the surface darkens before you sow.
- Mix the seed with dry sand and scatter it Tip a pinch of seed into a tablespoon of dry sand, mix, and sprinkle it thinly across the surface. The sand shows you where the seed has landed and spreads it far more evenly than fingers can, which matters because the seedlings are difficult to separate later.
- Press the seed onto the surface but do not cover it Tamp the surface lightly with a flat board or the base of a pot so each seed is in contact with the damp compost. Contact is what it needs, not burial. Covering the seed with compost or vermiculite will stop most of it germinating.
- Keep at 70 to 75F (21 to 24C) in bright light Stand the tray in the brightest position you have, or under a light held a few inches above the surface. A propagator or heat mat helps if your room is cool. Expect the first seedlings in seven to fourteen days; nothing useful happens below 60F (16C).
- Water from below and ventilate Stand the tray in an inch (2.5 cm) of water until the surface darkens, then take it out and let it drain fully. Never mist or water overhead. If you used a cover for warmth, take it off as soon as the seedlings appear so the surface can dry between waterings.
- Transplant at two true leaves Once each seedling has a pair of fleshy true leaves beyond the seed leaves, lift them by a leaf rather than the stem and move them into small pots of gritty mix, one or two to a pot. Handle them as little as possible; the stems are soft and bruise easily.
Sowing direct where they are to grow
Direct sowing works well and often produces better plants than tray-raised ones, because portulaca resents root disturbance and grows away without any check when it germinates in place. The condition is warmth: wait until all frost has passed and the soil at two inches (5 cm) deep has reached about 70F (21C). Sowing into cold spring ground wastes the seed.
Prepare the ground by raking it level and, if it is at all heavy or rich, working grit into the top few inches. Do not add compost or fertilizer. The ideal seedbed for this plant is thin, gritty and free-draining: the edge of a gravel path, the top of a dry wall, a bank, a strip of poor sandy soil at the front of a bed.
Scatter the seed thinly, mixed with sand, and press it in with the back of a rake or the flat of your hand rather than raking soil over it. Water once with a fine rose, gently enough not to move the seed, and then only if the surface is dry and the weather hot. Slugs take seedlings at this stage, so check at night for the first fortnight.
| Detail | Indoors | Direct outdoors |
|---|---|---|
| When | Six to eight weeks before the last frost | After the last frost, once soil is above 70F (21C) |
| Depth | On the surface, not covered | On the surface, pressed in, not covered |
| Temperature for germination | 70 to 75F (21 to 24C) | Warm soil; nothing below 60F (16C) |
| Days to emerge | Seven to fourteen | Seven to ten in warm soil |
| Watering | From below only | Fine rose, sparingly, only when dry |
| Final spacing | Transplant, then one or two per small pot | Thin to six to eight inches (15 to 20 cm) |
Thinning, hardening off and planting out
Thin direct-sown seedlings in two passes. Take out the weakest at the first true leaves so the rest stand two inches (5 cm) apart, then again a fortnight later to a final six to eight inches (15 to 20 cm). Thinning in stages covers you against slug losses. Snip the unwanted ones off at ground level with scissors rather than pulling them, so you do not disturb the roots of the plants you are keeping.
Tray-raised plants need hardening off over a week to ten days before they go out. Seedlings grown under cover have soft leaves that scorch badly in full sun, so increase their outdoor time gradually and give them shelter from wind. Once out, they want the hottest and brightest position you have, and they will not perform in anything less than eight hours of direct sun.
Pinch the tips out about two weeks after planting, once each plant is clearly growing away. Removing an inch (2.5 cm) from each shoot forces branching from low down and roughly doubles the number of flowers. The pieces you pinch off root readily if you dry them for a day and push them into gritty soil.
What to write down at sowing time
Record the sowing date, the temperature you germinated at, and the date the first seedling appeared. The gap between those two dates is the most useful number you can have, because it tells you whether your warm spot is actually warm enough and lets you time next year's sowing to hit planting-out weather exactly.
Note whether you started indoors or sowed direct, and in which positions. Comparing the two side by side for one season usually settles the question for good, and for many gardeners direct sowing into warm gritty ground wins outright once the soil is reliably warm early enough.
Finally, log the date the soil actually reached 70F (21C) at two inches (5 cm) deep, measured rather than guessed. Kept over a few seasons, that one date does more to fix the timing of everything else with this plant than any general advice about spring.