Gadenin日本語Get the appWater from below once the cover comes off
During the blackout the covered tray holds its own humidity and needs a light mist at most. The moment you uncover, that changes: the surface is exposed, the mat is transpiring hard, and a tray in a warm room will want water every day.
Water into the base, not over the top. Either sit the growing tray inside a solid tray with a quarter inch (6 mm) of water in it and let it wick up for ten to fifteen minutes, or pour water down one corner so it runs under the mat. Overhead watering from this point onward is the single biggest cause of rot, because water sitting in the crowded joints between stems does not dry out.
Pour off anything the tray has not taken up. Standing water under the medium for hours suffocates the roots and gives you the sour smell that always arrives a day before the collapse. The rhythm you want is wet, then drawn down, then wet again, never permanently saturated.
Judge by weight rather than by looking. Lift the tray each morning. A tray that needs water is noticeably lighter than one that does not, and after four or five trays your hands will read it better than your eyes read the surface.
| Stage | Method | Frequency | Warning sign |
|---|---|---|---|
| Blackout, days 0 to 3 | Light mist if surface pales | Once a day at most | Free water pooling on the surface |
| Uncovering day | Bottom water fully | Once | Mat wilting within an hour of light |
| Greening, days 4 to 7 | Bottom water | Once a day | Leaves dull and limp by evening |
| Last two days | Bottom water | Once a day, lighter | Stems soft and translucent at the base |
Still air is what kills a tray
A dense mat of shoots in a warm still kitchen is exactly the condition damping-off fungi want. The medium is wet, the humidity inside the mat is close to saturated, and nothing moves. You do not need a fan blowing on the tray hard enough to dry it out; you need the air in the room to be turning over.
A small clip fan on its lowest setting, pointed at a wall four feet (1.2 m) away rather than at the tray, is enough. It stirs the room without drying the surface. If a fan is not practical, leave the tray on an open shelf rather than in a cupboard or a closed propagator, and open a window for a few minutes twice a day.
Once the shoots are up and greening, stop covering the tray for any reason. Domes and plastic wrap after day four turn a healthy mat into a wet one overnight.
Trays stacked directly on top of one another to save space have no air at the mat surface at all. If you run several trays at once, stand them side by side or give each shelf enough headroom that air moves across the top of the crop.
Temperature sets the pace and the risk
Radish shoots run best at 60 to 70F (16 to 21C). In that band they take eight to ten days from sowing to cutting, the stems stay firm, and the disease pressure is low enough that ordinary care is enough.
Above 75F (24C) everything accelerates, including the things you do not want. The crop is ready in six or seven days, but the stems are softer, the pungency builds faster, and damping off goes from a rare accident to a regular event. If your only spot is warm, sow slightly thinner, water a little less, and plan to cut a day earlier than usual.
Below 60F (16C) nothing goes wrong, it just takes longer. A cool room stretches the run to twelve or thirteen days and the shoots are, if anything, crisper. The one thing to avoid is a cold draft on one side of the tray, which gives you an uneven mat you cannot cut level.
| Room temperature | Sowing to cut | Stem quality | Main risk |
|---|---|---|---|
| 55 to 60F (13 to 16C) | 12 to 14 days | Very firm, crisp | Uneven emergence |
| 60 to 70F (16 to 21C) | 8 to 10 days | Firm and straight | Little, if watered from below |
| 70 to 76F (21 to 24C) | 7 to 8 days | Softer, heat builds fast | Damping off in still air |
| Above 78F (26C) | 6 to 7 days | Soft, collapses easily | Rot at the base of the mat |
There is no feeding and no thinning
Do not fertilize. The seed carries everything the shoot needs for its whole life, and there is no point in the run where the crop is short of anything you could add. Feed goes into the medium, not into the shoot, and a fertilized tray of shoots is a tray with more salts around wet stems.
Do not thin either. The crowding is deliberate and mutual support is what keeps the mat standing. If a patch is genuinely too thick and staying wet, snip that patch out at the base with scissors and let the air in, rather than trying to pull seedlings out and disturbing the roots of everything around them.
The only routine handling is a daily look and a daily lift for weight. Beyond watering and air, the best thing you can do for a tray of shoots is leave it alone.
Keep a short log for each tray
Because a tray cannot be corrected halfway through, the value of records here is entirely about the next tray. Note the room temperature, whether you ran a fan, how often you watered and what the mat looked like on the day you cut. Two lines a tray is enough.
The comparison that pays off fastest is a warm tray against a cool one at the same seed weight. Most growers find they were sowing too heavily for their warmest room and about right for their coolest, and the log is what shows that rather than a vague sense that some trays go wrong.