Drying seedling tips

Started by Stromae, January 08, 2024, 04:03:10 PM

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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?


That is very warm compared to here - daytime temperature is whatever the weather provides although the minimum temperature will only ever be around 5-6C at any time of day or night.

Provided that there is good drainage, seedlings can be watered reasonably freely. That said, I would never use extremely high mineral compost - something like 50:50 coarse gritty sand:conventional potting compost - in my case John Innes (loam-based). If the picture shows your compost rather than a top-dressing (which I do not use for seed/seedlings), it seems almost devoid of any water-retaining component.

In my experience, seedlings only die-back in response to decreased and then no watering, so they will be green until March-April.

The 3-4-5 species that I have grown from seed have been easy to raise. Unless home-produced, the difficult bit is getting seed before it dies as all that I have known germinates in the seed capsule long before the capsule dries.

If the red item on the surface is a bulb, it should be 5-10(+)mm below the surface, in which case this implies your compost is wrong.


I fully agree with all points Cg100 makes. 22 degrees daytime temperatures may induce premature dormancy. Where are the plants? Greenhouse? Windowsill? A greenhouse may get much warmer than you think. 
I keep all my winter growing bulb seedlings outdoors with temperatures fluctuating which means they can go down to near freezing for a short time in a few early mornings. No losses to low temperatures.
I use a compost of half composted bark, finely ground and half washed sand. 
If you live in a frost free climate I would put the plants outdoors, if you get frost, make sure the maximum temperature does not go over 15 degrees C. Keep constantly moist.
Hope that helps 
Algarve, Portugal
350m elevation, frost free
Mediterranean Climate


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.


Okay, if you live in Canada, the cultivation of winter growing bulbs will remain a challenge. Much attention to detail is needed. I would assume that the mold is caused by constant high humidity in the propagator. You mention ventilation, though which should reduce humidity. Does water condense on the lid of the propagator? I did not really understand how you ventilate the propagator with outside air.
Apart from perhaps reducing the humidity if it is really too high, my idea is to use a systemic fungicide in intervals according to the manufacturer.
I do not have mould on the pots outdoors but my climate is frost free which allows me to sow winter growing bulbs outdoors. There can be mould on plants inside the greenhouse but that is definitely related to too high humidity in winter. I only very rarely use fungicides.
Another aspect: Janis Ruksans writes in his book ,,buried treasures"that he got much more diseases when he started to sterilize his soil. I never sterilize anything. But probably the commercial compost I use is treated in some way as it is totally weed free. But I also use my own compost from the compost pile (not for seed) for precious plants and never had a problem. Sometimes even small mushrooms appear in a pot without damage to the plant.
I do encourage you to experiment with different approaches.
Algarve, Portugal
350m elevation, frost free
Mediterranean Climate


When I grew many hundreds of cacti and succulents, I would sterilise everything for sowing seeds and did perfectly well. For bulbs I now assume that the commercial compost is "sterile" as is claimed (in reality it has been sterilised, but the bags have tiny holes so that they can be stacked for transport, so aren't actually sterile, but will be free from seeds).

With Strumaria and any amaryllid seed that arrives pre-germinated, I use either a cocktail stick or piece of stainless steel wire and make a hole deeper than the length of the  root that has formed and use tweezers to "plant" each seed with the actual seed sitting in the top of the hole. The bulbs always form under the seed, so they form below the top of the compost. I would not use any grit as a top layer for sowing, unless it is tiny - 2-3mm.

Based on you photo' I would suggest that you add 2-3-4mm of seived loam to the top of the compost mix in your pots -it will settle a little when watered/misted (I use a hand spray to water as it is more accurate and far more difficult to over-water). That loam should help the seedling anchor itself better

Mould that is visible is undoubtedly due to high RH. I am unsure why the temperature on a windowsill would go over 30C during the day though.

RSA has a minimum (winter) daylength in Cape Town of around 10 hours, and obviously it is longer as you travel north in RSA. As for your seedlings, they look essentially normal, apart from the yellowing, so light level must be at least close to being OK.

Growing SA winter-growers where you are is not going to be easy without considerable hassle and expense, unfortunately.


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 :))



The usual density of LEDs used in horticulture for growth, without any natural light, is 600-700W/sq. m, so yes, that will get hot if you are anywhere near that (they may be far more efficient than incandescent lamps, but well over 99% of the energy is emitted as heat).

A lot of people think of S African plants, especially succulents and bulbs, as universally growing in very dry habitats. That isn't so, very many do grow in seasonally dry, or even very arid areas, but it is seasonal and many have copius amounts of water during their growing season - quite a few species, even some Lachenalia, for instance, naturally grow in shallow standing water -a handful of species even have the specific name "aquatica" as a consequence.

As a guess, plants such as cono's are "designed" to lose rather little water while in growth. Bulbs may have fleshy leaves, but they require quite a bit of water when in growth in pots and, unfortunately, it is perfectly possible to have moist air above very dry compost.

Maybe the "simplest" thing to try is to separate the air flow so that most (almost all) cools the LEDs without getting near the plants, and then try growing the bulbs without covering them?


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%.


Unless your hygrometer is expensive, it is unlikely to be anywhere near accurate (by expensive, I mean $100+++++). Use a wet-bulb thermometer and tables - a "wet-bulb thermocouple" would be fine, although in confined spaces and/or with low ventilation rates, the evaporation from the wet bulb can add significantly to the RH.

(I was lucky when a factory where I worked, closed - I won a Vaisala electronic hygrometer.) https://www.ebay.co.uk/itm/132943648081?chn=ps&norover=1&mkevt=1&mkrid=710-153316-527457-8&mkcid=2&itemid=132943648081&targetid=4585513252137470&device=c&mktype=&googleloc=&poi=&campaignid=554609237&mkgroupid=1310618964595038&rlsatarget=pla-4585513252137470&abcId=9320693&merchantid=87779&msclkid=ab88d1482bdc1de20d6ab4d79814b6e6

You obviously know all about humidity calculations and how they work.....

RH during the UK winter in a greenhouse is going to vary quite a bit depending on weather as sunny weather will warm a greenhouse by quite a bit, which will obviously drop the RH. Outdoor RH in the UK is very, very rarely below something like 40-50%.

A far better and very accurate way to view humidity in the UK is to look at dew point. It is surprisingly accurate to assume that the maximum dew point during the day is around a degree or so above the minimum night-time temperature the previous night, minimum temperature is usually an hour or so before dawn. So, if the minimum night temperature is 5C, the maximum dew-point during the day is likely to be around 6C. If the maximum temperature during the day is 20C, that is an RH of 40%

%2Fexp [17.625 × T%2F (243.04 %2B T)]}.]Relative Humidity Calculator (omnicalculator.com)

In winter maybe the average minimum night temp. might be around 0C over a great deal of the country. In a greenhouse it might get to 10C during the day, maybe a little more if we get decent sunshine. That is an RH of around 53%. Come night time, most people would keep a minimum of something like 5C - that is an RH of 73%.

If your greenhouse has a soil floor, or leaks a bit, or it is crammed with leafy plants, RH will obviously often be higher, and how well sealed and insulated the greenhouse is has an effect (most UK greenhouses are not well sealed or insulated - stand inside one in a strong wind and that is obvious).

That said, minimum winter temperatures over lowland Britain are frequently/routinely a (very) few degrees above 0C - so far this winter - I live not far from Birmingham - I have seen only one real frost, although we are now in a period of night time temperatures hovering around 0C.

This is all pretty rough, but at the same time close to reality. (I worked in industrial  heating/ventilation/dew point/RH control for a while, plus my background is science through and through).

I should also say that for some psychological reason, many people (at least in the UK) see 50% RH and regard it as high humidity, mostly because people have no clue about atmospheric RH, presumably. It isn't high - put washing out to dry in 50% RH and it will dry PDQ.

IR is normally filtered out in critical applications, using (circulating) water.......................

What is the distance between plants and LEDs? What colour LEDs?

Science and commercial horticulture usually use moles/sq m/day as a measure of illuminance, rather than lux - something like 10-12 moles/sq. m/day is where commercial set-ups (and illicit operations) aim for.

One extra tip - I use wooden cocktail sticks (usually bamboo these days), or lengths of wooden kebab skewer in pots to judge how damp they are - just push them in close to the edge and when you want to know dampness, just remove and touch to your lips.
Cocktail stick work in pots to maybe 7cm, cut suitable lengths of kebab skewer for larger pots.
It works well for me - all pots of water-sensitive plants get the treatment.