I started with some chilli seeds of varying types planted in some Gro-Sure Seed & Cutting compost (https://www.gardenhealth.com/product/grosure-seed-cutting-compost).

After a few weeks sitting on a heat map they started to appear. It was at this point I turned the grow lamp on for 12hrs a day as well with the lid down:

My Seed container

I watered once a day keeping the soil damp, but once the seedlings showed their first two leaves they wilted and looked pretty much dead or dying:

enter image description here

Any ideas would be much appreciated as to what I'm doing wrong... Maybe the lid shouldn't be on, or higher up... Maybe they can't breath, I don't know... I'd say inside the box it's warm, not hot, so I don't think it's too much heat, especially when its still quite cold at the moment in England UK (they are inside in my workshop).

Thanks for the comments guys, I've updated the setup now so that the seedlings (what's left) are outside..I have the grow light on from 0700 to 2200 with the heat matt coming on at 2200 to 0700: enter image description here enter image description here

  • What's the actual temperature in the grow box? Mar 8, 2018 at 21:06
  • 1
    I am an amateur, but it looks to me that the seedling shouldn't be closed in a box. I've read that even if the seedlng are not in a box, some people run a fan ovet the containers to improve air circulation.
    – VividD
    Mar 8, 2018 at 22:07
  • Graham, my thought as well...TOO HOT. They got cooked.
    – stormy
    Mar 9, 2018 at 7:06
  • I'm not sure what the temperature is, I need to get a thermometer. Mar 11, 2018 at 14:17

3 Answers 3


You have cooked your baby plants! Get rid of the box, if you are growing indoors you do not need a heating mat. You do need thermometers; for soil and for the air. You will need to get a great fan to blow air. Easy to begin again.

I would use a 'dome' over your seed starting tray or fashion saran wrap to hold the heat and moisture until your starts show their second or third set of leaves. You need a thermometer to judge the temperature caused beneath a dome, saran wrap or in a reflective...oven. Do not soak the soil. Just the top quarter inch containing the seed should be kept moist.

Use potting soil without fertilizer, without moisture retention gimmicks, without compost. Just plain potting soil in your little pots to start seeds. Continue to use plain potting soil as long as your plants are in pots. Do not allow water to stand at the bottom of your pots. Raising the bottom of the pots off the surface so water tension doesn't inhibit drainage is also a good thing. No rocks, sand, gravel...no compost belong in pots. Just sterilized cheapo potting soil.

After seeds break surface the light should be on 18 hour days, not 12. I am reading that there is too much water in your equation; sitting in water, being sprayed with water and staying moist is not at all a good thing. Seedlings are tougher than that and just a little too much moisture will cause rot. That is why the use of a plastic dome or saran wrap is helpful at the very beginning. Watering is minimal when growing under a plastic dome, terrarium or saran wrapped seed trays. Very minimal.

Once you've got your second or third set of leaves the dome or saran wrap comes off. The fan is turned on. Those leaves should actually move in the breeze caused by the fan. That fan is on 24/7. The purpose is reducing fungal problems. Air movement is extremely critical. We also prune a bit if leaves are in excess, to allow air flow. Move pots away from one another.

Those lights might be fine at that height if your plants were on a flat surface and not in an oven. Also, you have to have a fan blowing the air. This also moves the O2 the plants made away from the leaf so the leaf is better able to uptake CO2 which it needs to do photosynthesis to make the plant's food. You need a thermometer (50 degrees is the low and 80 is the very highest...degrees Fahrenheit) and humidity monitor (depends on your plants but low humidity is a good thing).

You need to use timers. Start at 18/6 then when flowering starts (a month or two down the road) you switch to 12/12. (Plants in the dark stay in the dark undisturbed during this time, no cracking open a door and letting in light...you can use a green light).

Make sure your fertilizer is lower in N than in P and K. So NPK formulation of 5-7-6 would be perfect. Even even numbers such as Osmocote 14-14-14 extended release used at half the amount of applications would work. You add too much Nitrogen and you won't get flowers and chilis.

White Fly has been the biggest problem with growing chilis. Keep an eye on your plants...do not bring any strange plants with strange soil into your grow room. No smokers touching plants or smoking near plants.

Sorry, forgot about pollination. All you need to do each time you water and your plants are in flower, before watering, is shake the plant. A good shake not so hard to break limbs, leaves but this will pollinate your plants to make fruits, chilis.

  • Thanks for the comments, I've updated my question with my updated setup...I Will get a fan and a thermometer...Thinking about setting up a Raspberry Pi to control and monitor it... Mar 11, 2018 at 14:19

You could bake bread in that box. I use a horticultural heat mat on a timer for 8-10 hours starting at midnight. The ones I use range 24°C-30°C and are thermostatically controlled to adjust with ambient air temperature.

Full spectrum LED grow lights, 1200 Watts set 40-60cm over the soil surface, timer as well set 12 hrs. ON beginning at 0600 - as much as an average Spring day cycle. The average room temperature is ~20°C, could drop as low as 10°C. LED’s are much hotter than many suspect.

I cover seed sets until the seed leaves are green and first adult leaf buds appear then remove clear plastic cover. Soil is always moist, mist twice per day and bottom water in tray. I start in March, plant outside in May. Location New York City, USA. Current outdoor temperature is 0.6°C.

Keep the lights - lose the box

Thai peppers in upper left tray - typical starting setup w/white LED

  • Full spectrum LED grow lights, 1200 Watts? 1200 Watts? Do you get your electricity for free?
    – Tom
    Mar 28, 2019 at 10:33
  • No, I do not get electricity for free but that’s a question for another stack.
    – herb guy
    Mar 29, 2019 at 11:50

You need to get the atmosphere more humid, your atmosphere seems to be too arid. Remember chillis thrive in essentially a sub-tropic climate, they are going to wilt and die if there is not enough moisture around.

I have found solutions like these to be a great help in ensuring enough moisture in my chili growths.

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