Gadenin日本語Get the appGermination is a temperature problem, not a light problem
A melon seed needs soil at 80 to 85F (27 to 29C) to germinate promptly, which is warmer than most houses and much warmer than a windowsill in early spring. At that temperature seedlings appear in four to six days. At 70F (21C) they take two weeks and come up unevenly, and below about 65F (18C) most seed simply rots in the compost before it can sprout. A heat mat, an airing cupboard or the top of a refrigerator will do the job; a bright cold windowsill will not.
Light matters only once the seedlings are up, and then it matters a great deal. The moment the first shoots appear, move the pots to the brightest place you have or put them under a grow light within a couple of inches of the leaves. A seedling left in warmth and dim light stretches into a pale, floppy stem within days and never makes a good plant, so the move from heat to light is the point where most home-raised melons are lost.
| Condition | Soil temperature | Days to emerge | Result |
|---|---|---|---|
| Heat mat or warm cupboard | 80 to 85F (27 to 29C) | 4 to 6 days | Fast, even, strong seedlings |
| Warm room | 72 to 78F (22 to 26C) | 7 to 10 days | Acceptable but slower and less even |
| Ordinary indoor temperature | 65 to 70F (18 to 21C) | 12 to 18 days | Patchy, and some seed rots |
| Cold windowsill or unheated frame | Below 60F (16C) | Rarely | Most seed rots before germinating |
Move the pots off the heat the day the shoots break the surface. Continued bottom heat plus indoor light is precisely the combination that produces long, weak, useless seedlings.
Sow into individual pots and sow late
Melons hate root disturbance, so sow into individual pots three inches (8 cm) across, or into deep cells, rather than into a seed tray you will have to transplant. Put one or two seeds per pot, half an inch (1 cm) deep on their edge rather than flat, and thin to the stronger seedling with scissors once the first true leaf shows. Pulling the weaker one out drags the roots of the one you are keeping.
Sow only three to four weeks before you expect to plant out, and resist sowing earlier. Melons grow fast in warmth, and a plant held in a pot too long coils its roots, checks, and never establishes properly. A three-week-old plant set into warm soil will overtake a six-week-old pot-bound one within a fortnight and fruit earlier. If your planting date slips because of cold weather, pot the plants on rather than letting them sit.
- One or two seeds per pot Sow into individual three inch (8 cm) pots of moist all-purpose potting mix, half an inch (1 cm) deep. Thin with scissors, never by pulling.
- Sow the seed on its edge A flat seed can hold water on its upper face and rot. Standing it on edge lets water run off and improves the strike rate noticeably.
- Keep the compost damp, not wet Melon seed rots easily. Water once at sowing, cover the pot to hold humidity, and do not water again until the shoots appear.
- Count backwards from your planting date Work out when the soil in the bed will reach 65F (18C) and sow three to four weeks before that. Sowing to the calendar rather than the soil is the usual mistake.
Growing them on without checking them
For the two or three weeks between emergence and planting out, the whole job is keeping the plant growing steadily without a single check. A melon seedling that is chilled, dried out or starved recovers slowly and carries the setback for the rest of the season, and cold nights are the usual culprit: keep them above 60F (16C) overnight even if that means bringing them in off a greenhouse bench.
Water in the morning so the compost is not cold and sodden overnight, and give a weak liquid feed once the first true leaf is fully open if the compost has no fertilizer in it. If planting out is delayed by more than a week, pot up into a larger pot rather than letting the roots circle the bottom of the small one. A plant that has already started to run in its pot is worse than a smaller plant, not better.
| Symptom | Cause | What to do |
|---|---|---|
| Long pale stem, leaves far apart | Too little light after germination | Move to the brightest place immediately; bury the stem when planting |
| Purple undersides on the leaves | Cold roots restricting phosphorus uptake | Raise the night temperature; do not add fertilizer |
| Seedling collapses at soil level | Damping off from cold, wet compost | Improve airflow, water in the morning only, discard affected pots |
| Pale yellow leaves, growth stalled | Nutrients used up in the pot | Weak liquid feed, or pot up into fresh compost |
| Roots circling at the bottom | Held in the pot too long | Pot up now; do not tease the roots out |
Hardening off and the planting-out decision
Harden the plants off over about a week before they go out, moving them outside for progressively longer each day and bringing them in at night for the first few. A melon taken straight from a warm bright indoor spot to full sun and open wind scorches its leaves and stalls for a fortnight, which costs more than the week of hardening off would have.
Then wait for the soil, not the calendar. Push a soil thermometer four inches (10 cm) down at mid morning on three consecutive days and take the lowest reading; plant only when that is above 65F (18C). Warm afternoons over cold nights mean nothing to a root system. Waiting an extra fortnight for warm ground almost always produces an earlier harvest than planting into cold soil, which is counterintuitive enough that most gardeners have to learn it once for themselves.
- Warm the bed in advance Lay black plastic or a woven black mulch over the planting bed two to three weeks ahead and plant through a cross cut in it. In a cool climate this is the highest value thing you can do.
- Plant at two or three true leaves That is the right size. Set the rootball level with the surface of a raised hill, never buried, because a stem sitting in damp soil rots at the collar.
- Handle the rootball whole Slide the plant out intact and set it down. Do not tease the roots out as you would with a tomato; melon roots break easily and the plant checks badly.
- Cover for the first fortnight A cloche or row cover over each plant for two weeks keeps off wind and cold nights. Take it off the day the first flowers open so pollinators can get in.
Water the planting hole and let it drain away completely before setting the plant, then water in and keep the soil merely moist for two weeks. Sodden soil around a plant not yet drawing water is how young melons are lost to root rot.
The numbers worth recording at this stage
The seedling stage is short and it is easy to forget what you did, but the dates from it explain the whole rest of the season. Write down the sowing date, the date the first shoots appeared, the temperature they germinated at, the date you planted out and the soil temperature that day. Five numbers, all recorded in under a minute each.
A year later those numbers answer the questions you will actually have. If the plants were slow all summer, the germination temperature and the planting-out soil temperature will usually show why. If fruit ripened too late, the sowing date tells you how much earlier to start, and whether the answer is to sow earlier or simply to warm the bed better before planting.
- Record sowing and emergence dates The gap between them is a direct measure of how warm your germinating spot really is, whatever the thermometer on the wall says.
- Record the soil temperature on planting day This one number explains more slow starts than anything else. Take it four inches (10 cm) down at mid morning, not on the surface.
- Note how long they sat in their pots If planting was delayed, write down by how long and whether those plants caught up. It sets your sowing date for next year.
- Note losses and what they looked like Damping off, cold damage or scorch after hardening off all look different. Recording which one you had tells you what to change.