PBS Forum

Quote from: Arnold on April 12, 2025, 12:26:31 PMI've read that you can use the light meter in a good camera to measure light source using a grey card.

Have you seen or heard of this?

I tested this, because I used to do a talk on artificial light for orchids and it's one of those questions that always comes up. I had a couple of pretty expensive DSLR cameras around, and thanks to a friend not all from the same maker, and I couldn't find any good correlation to either my lux/footcandle or much more expensive PAR light meters.

I didn't reach the level of scientific rigor required to definitively say there's not a way with some particular camera and lens and reflective surface and technique, but I tried a grey card and several types of white surfaces, at different angles from  the camera lens pointed as directly down at the measured surface as possible without casting shadows to a rather shallow angle, and with several different light sources and a couple of lenses. The meters have diffusers and can be pointed directly at the light sources, but pointing the cameras directly at the light sources gave wildly variable numbers depending on the exact angle, and was very much not recommended for at least one (e.g., the sun) so the cameras were always seeing reflected light.

A side note - one thing I tried that surprised me by working, and rather well, was an app for my phone to measure color temperature. I tested it against several LED sources of "known" color temperature, and in every case the phone app was close enough. It's handy for photography.

Steve

Quote from: Uli on November 16, 2024, 01:01:12 PMI have never used hydrogen peroxide for my plants. This idea seems odd to me. Hydrogen peroxide is a strong oxidizer. In the medical it is used to clean and disinfect, it removes organic detritus, blood and the like. Or think of bleaching hair.....
It may depend on the concentration but I would worry about causing more damage than good by using this for plants. And how to apply? Water a pot with substrate? For how long would it be active in the substrate? Or rinse bare roots?

Quote from: Bern on November 15, 2024, 04:55:41 PMI just tested my tap water and the pH is about 8.5.  So, I will adjust the pH to a bit below 7.0 and I hope that this will help the plants absorb the fertilizer and trace nutrients better, and maybe help to resolve the yellow leaves problem in my Griffinias.

Quote from: CG100 on November 16, 2024, 11:55:43 PMI would suspect that most rain is on the acid side of neutral today given that it will absorb only neutral of acidic gases from the air.

Hydrogen peroxide. We began using H2O2 on the advice of a friend who's been a commercial orchid grower, on a fair-sized scale, for decades. One of his degrees is in plant physiology. (Those things don't mean that he's always right, but I'm citing them to show that his credentials are much stronger than mine!) He uses it for bacterial and fungal rot issues, and advises buying a new bottle of the common 3% solution and pouring some all over the affected parts of the plant each day for several days. He does not rinse the H2O2 - it degrades so quickly there's no point - nor does he worry about getting it in the medium or on the roots. We had a Phalaenopsis with crown rot, which is fast moving and almost invariably fatal within a few days, so with nothing to lose we tried his advice. The plant recovered. Maybe that's a fluke, maybe not, but we were converted and now use H2O2 regularly. We've never seen any indication that it harms even sensitive roots.

pH of water systems. I've been told by several people, including someone who worked at the treatment plant of our local water authority, that many systems artificially raise the pH of their treated water to minimize corrosion in the pipes. Since the pipes we see going in these days are all plastic, maybe that's a relic from the past. Our tap water is also around 8.5, but by the time it comes out of the RO system it's down where it needs to be for better nutrient uptake.

pH of rain. Acid anhydrides in the air (carbon, sulfur, and nitrogen oxides) will quickly dissolve into very pure water and lower the pH. A research chemist who was also a plant person told me that if he left a beaker of his ultra-pure water (kept under inert gas) out in the air for 15 minutes to answer a phone call, the pH would be lowered so much he'd have to pour it out and start over. I believe equilibrium pH for pure water left standing is generally around 5.6-5.8, but it's been a long time since I saw that so ... I can say that the pH of just-fallen rain here (NW Arkansas, USA) is in the low 6 range.

Viruses in general. As with lily growers, a big topic for orchid growers, and a huge amount of misinformation out there. There are simple antigen tests for a couple of the most common orchid ones, but I'm not aware of any for amaryllid viruses. In orchids, there is no cure, but it's sometimes possible to produce virus-free clones from meristem tissue, and the common orchid viruses aren't seed-transmitted so with care virus-free offspring can be produced. Again, I don't know about amaryllids. I have seen a report of curing a virus-infected amaryllid but it involved essentially cooking the bulb for some time at a very precise temperature which the bulb could - barely - survive but was fatal to the virus (!). Bern, I would not rush to discard your plant as having a virus until you're convinced it's not environmental, but I would isolate and watch carefully.

Steve

I can't help with the original question about L. agavoides, but FWIW all my Ledebouria and related genera are in a greenhouse and get water year-round, and don't seem to care. They put out new growth and flower in the spring and go dormant in the fall. Some lose all their leaves, some just stop growing and get increasingly ratty looking all winter. I do try to water them less when they're not actively growing, but they get some water at least every couple of days. They're in a well-drained mix, and I've never had any problems with rot.

Steve

Lee, thanks for this! That's a great summary that I'm sure took some time to generate, and I appreciate the work. I've had a tab open to the thread since you created it, and finally had a chance to spend some time on it.

Is the Garcia paper easily available, or behind a paywall somewhere?

Steve

Hi Anita,

I don't stratify, and sow as quickly after harvest as I can. I've never tested to see if they'd germinate after dry storage but I suspect it would be much reduced if at all. I usually put the pots near the edge of the greenhouse, which is frost-free but can get down to the low 30s F (near 0 C) briefly on the coldest nights.

But here in NW Arkansas, US, USDA zone 6 or 7, the ones I don't collect and just let fall where they will outside germinate and do fine on their own, even in areas that are not mulched other than whatever tree leaves fall. While digging Lycoris to give others, I've encountered these seedlings, and the radicles can go 6 in (15 cm) into the soil with no leaves showing until the next growing cycle, so don't give up if you don't see action above the soil right away.

There's always an exception so maybe x squamigera does make a viable seed now and then, but in about 35 years I've never had one make any seed at all. They always appear to be setting pods, which always yellow and abort with no actual seeds inside.

There are other Lycoris growers a lot more knowledgeable than me here, I hope they'll chime in.

Steve

Quote from: CG100 on September 09, 2024, 10:01:37 AMEvery day is a school-day.

Never heard of Amorphophallus being propagated via leaf cuttings before.

Assuming that all Amorphophallus are actually Amorphophallus, is this possible with all species?

It's a big genus spread from Africa to Australia and a wide range of habitats, and probably many have never been tried. But it seems most can, though the success rate varies widely from species to species. Oddly, to me anyway, A. konjac, which is the hardiest (it's survived -20 F [-29 C] in the ground here several times), probably the most commonly grown, and which offsets prolifically, is rather difficult to propagate from leaf cuttings. Others, like A. parvulus (now harmandii) are almost 100% if the cutting is taken at the right time. I've not tried any of the really tiny ones like myosuroides or ongsakulii.

My experience is that rooting leaf cuttings of the tuberous aroid genera in general varies widely. I think every leaflet of Gonatopus boivinii that falls off and lands on soil will root and form a tuber with no help. I used to find them all over the place in the sun room. But I've tried leaf cuttings of Taccarum weddellianum, several times with no success. I've also failed with the very few Arisaema leaves I've been willing to sacrifice to experimentation, but I think Tony has had some success in that genus.

Steve

Hi Aad,

I've been propagating Amorphophallus this way for more than 30 years now, but just casually, to make plants to give friends. The PDN link you posted is by far the best write-up I've seen, and has data on the most species. They're the experts.

A couple of comments. PDN removed 2/3 of the leaf, leaving 1/3 to provide energy to the existing plant. I've never been that brave, and always stop at 1/3. For larger species, that 1/3 can be divided into 2-3 cuttings (or more), as they did, but for smaller ones I just leave it a single cutting. I have no scientific data to support this statement, but it seems reasonable that there is a minimum leaf area needed to collect enough energy to produce a viable tuber before the natural senescence of the leaf occurs.

Timing of the leaf cutting seems important. PDN suggests waiting about 4 weeks after leaf emergence to take cuttings, and I'd agree. But at some point, as the leaf ages, the likelihood of success from cuttings of it goes down dramatically, and my experience is if there's the slightest bit of yellow, indicating the leaf is beginning to senesce, there's no chance at all. This still leaves you usually some weeks of viability, but don't want too long.

Without a commercial propagation setup like Tony's, after application of rooting hormone I stick them in damp perlite and put in a plastic bag (ziploc) with the top folded over but not sealed, and in bright light but not direct sun. Then wait. Don't let the medium dry out. Eventually the leaf turns yellow, collapses, and disintegrates, just as it would on the plant, and that's when I dig into the perlite to see if there's a tuber or not.

Good luck!

Steve

Quote from: CG100 on September 05, 2024, 10:06:56 AMPresumably seed is not ephemeral, even if not long-lived?

Germination - gentle warmth, bottom heat?

My experience is only with those 2 species (hasseltii & gardnerianum) but for them, yes, except that I didn't find bottom heat necessary - both germinated well enough at room temperature and in a reasonable time, i.e. weeks not months.

I collected seed from my hasseltii several times over the years I had it, so more experience with it. It's been a while, but I believe I sowed it as much as 5 or 6 months after collection, stored at room temperature, and didn't notice any difference in germination. But years later, after I lost the plant my friend sent me and had given away all the offspring, I found some old seed I'd saved and didn't get any germination.

Steve

I've grown only two, H. hasseltii and H. gardnerianum. H. hasseltii is a smaller species and I kept in in the sun room, as I'm sure it's not hardy here (NW Arkansas US, formerly USDA 6b, now 7a, FWIW). I've since lost it, which I hate because it's a great plant, attractive all the time and the fragrance of the flowers, especially at night, was wonderful. I'd love to have it again now that I have better conditions. It was not a rampant grower.

H. gardnerianum I grew from seeds donated by Alberto Grossi to BX 143 in 2007. By then we had a greenhouse and I put it in a 3 quart pot on the floor at the base of a bench. It's a much larger and more vigorous species and I can easily believe that it could be invasive in the right climate. It split that pot long ago, settled on the dirt floor, and has been going strong since with no assistance from me. It flowers every year - I think another spike will be open soon - and goes dormant every fall, though late growths like this one may hang around into October or November before dying back and dehiscing neatly at the top of the rhizome. The greenhouse is always above freezing, but temps on the floor reach the 40-50 F (5-10 C) range, maybe a little lower, on cold winter nights. I believe this one is considered hardy to USDA z7, and there is so much of it I'm going to try a piece outdoors this winter, well mulched. To me fragrance is a little strong close up but quite nice when I walk into the greenhouse when it's blooming, and the inflorescences are impressive.

Steve

My experience matches CG100. I get germination if sown within several months of harvest, but the sooner sown the better the percentage. I've never had year-old Drimia/Drimiopsis/Ledebouria germinate.

I sow them in a well-drained mix. When they germinate, I let them guide me. If they seem to want to go dormant, I back off the water and let them. If they stay green, I keep watering them.

Steve

As far as I can tell, if you have the basic information - temperature, air pressure, and partial pressure of water vapor - then RH, dewpoint, and VPD are different ways of looking at the same thing. There are formulas and tables that let you get to any of them or convert between them. I grew up with RH. The weather people now, at least in the US, like dewpoint, for technical reasons, and the crop science people like VPD, also for technical reasons.

I also use Bluetooth enabled sensors (SensorPush), and it lets me display any or all of those three values. I tend to look at RH first since I'm most familiar with it, but I've got the VPD display turned on and am trying to get used to looking at it for the greenhouse sensor.

I agree strongly with Peter that leaf temperature is in many, maybe even most, cases, more important in knowing whether the plant is too hot than is air temperature, especially with C3 plants. High levels of photorespiration can become detrimental very quickly. (What I can practically do about that in my growing situation, other than more shade, is unfortunately a whole other question.)

The only real use I make of any of those numbers is deciding whether to spray water on the GH floor to increase RH/reduce VPD for the cuttings and seedlings, since they're so sensitive to water stress.

Thanks for the link to "Plant Empowerment", Peter. Looks like some good information there.

I can't help with the question, as I've never gotten seeds from either of the two Velloziaceae I have - this one, Xerophyta retinervis, and X. (formerly Talbotia) elegans. 

I don't want to hijack the thread, but if you have advice on pollination, I'd love to hear it. X. elegans in particular flowers freely every spring, but has resisted all my attempts to self it. I don't know if this is due to self-incompatibility or if there's a trick, and haven't found much information.

A friend who spent time in Brasil with Burle-Marx and saw a lot of Vellozia in habitat, and grew some, thinks it should be straightforward, but Xerophyta are from the African branch of the family so ??

I'd also appreciate a pointer if anyone knows of sources for other Velloziaceae.

Steve

Depends very much on the size/shape of the flowers and the particular species, since some things have special requirements. But for general pollination I use cotton swabs a lot, sometimes clipping or shaping the cotton a little, sometimes dry, sometimes damp. Very cheap, available in quantity, disposable (the ones with paper spindles are compostable), and seem to work pretty well. If I'm doing controlled pollinations among specific plants I can mark the spindles with a felt-tip pen to help track whose pollen is where.

I haven't tried Lachenalia, but have had good results with them on various Ledebourias.

Steve

Quote from: David Pilling on September 24, 2023, 10:01:36 AMspider repellent... things like ticks and chiggers are spiders, and things like deet are repellents for them.

Or if not repel them, at least leave them confused:

https://www.sciencedaily.com/releases/2018/09/180926140832.htm

Steve

Lee, this is very interesting. I've been fascinated by color since I heard a talk by an ornithologist who was studying the visual system of birds (this was back before I paid much attention to birds, so I don't recall now why I was even there). He showed examples of colors that looked identical to most humans, but were composed of different frequencies of light and look very different to birds. Many birds are tetrachromats, with different color sensitivities than ours, including into the ultraviolet.

I started casually following the efforts of plant breeders, and in some cases gene shufflers, to achieve colors not found in nature, such as the blue rose or blue Phalaenopsis orchid (which was modified to produce the blue pigment in Delphiniums). But I hadn't considered the question you asked, which is a great one. And I like your answer! I've seen pictures of 'Masquerade'. If only I could keep Anigozanthos alive.

David, re your question of other ways to produce color than pigments, some plants also produce "structural color", derived from the way light interacts with nanoscale structures. (As do some birds and insects; I've read that all blue color in bird feathers is from structure rather than pigment.) I've been slowly accumulating research papers on this topic for years, and still don't have very many.

You also reminded me that I saved a couple of papers on how to use a cheap plastic diffraction grating and the standard camera in a smartphone, with some software from the Android app store, to make a spectrometer. I need to dig those out and actually try it. One more project for my overflowing list.

Steve