PBS Forum

I didn't know about 600-700W/sq. m! I was adding more LEDs until my plants stopped being stunted in the winter, and ended up with exactly 600W/sq. m. My initial idea was indeed to ventilate only the LEDs (I have them separated from the plants by glass), but that does not work out in practice. Plants still get hot from the IR and at least some air flow is needed over the plants. What is your usual RH during the growing season? My hygrometer shows RH of 30-45%, but I am not sure I can trust it. Psychometric calculations show that once the outside air is warmed up RH should be more like 10-20%.

I cover my seedlings with plastic film, otherwise they would dry out within an hour. The outside air that I use for cooling is very dry. My propagator has a ventilation duct that sucks air from outdoors, and then expels it back to the outdoors via another duct. The freezing air cools the LED lights and the seedlings. This set-up works at least OK for the Conophytums that grow in the same places as the bulbs of SA. If I don't use the lights, nothing would grow, literally. We have very thick clouds for weeks at a time with windowsill light levels of a dim basement. Even very dark-tolerant plants don't do well without artificial light. Ventilation of the lights is necessary because otherwise they get very hot. Temperature goes from -20C at the intake to +25C at the exhaust. These are high-intensity LEDs, not your households ones. So, yes, growing winter growers in Canada is a pretty expensive enterprise, but I have it all mostly set-up. I just need to fine-tune it for the bulbs.

I never use commercial soil for anything. In Canada, what they sell as "compost" is just ground landfill filler. It is full of uncomposted leaves, branches, saw dust, massive amounts of plastics, glass, etc. I use loam from the backyard. It has to be sterilized, otherwise mold will overgrow anything and everything (ask me how I know

Thank you very much for your advise! I am in Canada, so everything is frozen more than I would like it to be I keep the seedlings in a propagator-type box with artificial light and ventilation by outside air. At night their temperature goes down to 5-15C. I find it the only feasible way to grow species that need more light. On a windowsill one can provide artificial light, but the temperature would go above 30C, hence the need for ventilation by the outside cold air. And because of ventilation, I need to keep the space enclosed, since I don't appreciate my house going down to 5C at night.

I will keep in mind to not go over 15C during day. The seedlings are in 50:50 mix of loam and mineral content. The grit in the photos is the top layer. Without it watering would disturb the seedlings when they just hatch. The red think is indeed a bulb. I sow them on the surface. Should the seeds be covered?

How do you keep seedlings constantly moist without molding them? I wash my pots in bleach and oven cook the soil, but still get mold, like on the photo below. It starts on the seed coats, and then spreads. Removing seed coats is not practical as they are often attached to the seedling.

My 3-month-old seedlings of Strumaria all of a sudden started to yellow their tips, followed by drying the plant. I seems to be too early for them to dry out. I keep them at about +22C daytime, and +10C at night. I keep them moist. What might this be?