I wanted to throw in a possible hypothesis that I’m trying out this autumn/winter with respect to larger seed starting pots vs smaller seed starting pots. I have always used 4-in/10-cm pots to start my seeds pretty much all the time. Since I live in a mediterranean climate (southern California), I’ve never had to worry about the weather for starting seeds of species from other mediterranean climates (such as the Cape region of South Africa, Chile, or the Mediterranean itself). Way back when, I settled on 4-in/10-cm pots instead of the tiny pots (6-cm?) that Gastil describes or large six-pack trays that are of a similar dimension. This was because the number of seeds in a packet typically was too many to go into one such small pot, but not usually enough to need anything larger than the 4-in/10-cm one. Plus, they were large enough that, as Uli states, they don’t dry out as quickly as those tiny pots, especially since I make a custom seedling soil mix that has much better drainage than the commercial seedling soil mixes. And the seedlings can stay in the same pot for several years. This has worked out quite well in general. However, over the years there have been a stubborn few species that I have never gotten to germinate. Although I have seen evidence from others that they’ve gotten them to germinate seemingly without any trouble. So I’ve kept trying. In particular, I’ve noticed that the seedling size plants I’ve gotten from Dylan Hannon, who is the curator of the Conservatory and Tropical Collections here at the Huntington Gardens, always are grown in a very high pumice containing mix in individual tiny pots like the ones Gastil describes (6 or 7 cm pots). Now for a side story that relates to my possible hypothesis. A recently hired young co-worker of mine who grew up in a much colder climate than here, was raised growing a vegetable garden with his parents. He was eager to try growing a vegetable garden here with our much milder climate and two growing seasons per year. Plus, there were species he never could grow before, such as citrus so he bought some dwarf varieties and is growing them in large tubs. As he explored further into new things he could grow here, he also wanted to grow some of his favorites. Some of them are grown here during the winter rather than the summer (such as snap peas and broccoli). But one day he came to me, sad, because he had researched some into trying to find varieties of rhubarb he could grow here in California in the lowlands, and had determined that it wasn’t possible because they require much colder winters than we get here. So I thought, in this day of Google, maybe there was a variety out there that might just barely survive and grow here, even if not all that well. He and I Googled for a few days, and all of the hits here in the U.S. were of attempts to grow it as an annual, in the shade, etc. But then we found a reference to a variety that Luther Burbank developed from a scrawny unusual variety that someone in New Zealand sent him. It turns out that that led to a thriving rhubarb industry in California that supplied the nation’s needs during the winter when all the other growers, in colder climates, stopped producing it. The winter growing varieties proliferated and we even found a nursery here in Pasadena (that no longer exists) that once put out catalogs with 10 different varieties that grew in California. This all dwindled almost to nothing as Americans stopped using rhubarb, although there was a brief resurgence in the early 1990s, with a farm of a several tens of acres about 15 miles east of here. Those growers had developed an improved variety that was their mainstay. They eventually sold their land to a housing developer and some random guy bought out his rhubarb and started a farm down in the San Diego outskirts. But he eventually sold out to a housing developer, too. It appeared to dead-end there, although I did discover that the Luther Burbank society up in northern California was trying to recover as many of Burbank’s varieties of everything that they could find, and that they had gotten their hands on 3 or 4 of one of Burbank’s original varieties of rhubarb, but had none to share at this time. I searched just a little bit longer, and somehow got a hit on rhubarb growing in Australia. It turns out that at around the same time that Burbank got his start of that winter growing variety, some Australians got a hold of some similar types themselves. They developed and proliferated a bunch of different varieties including some that grow well in the highlands of Queensland. And there was at least one family that has continued improving on various rhubarb varieties that grow not only in Australian winters, but during their summers as well. That family sells seeds of their best varieties, and I was able to purchase three of their top varieties for warm climates early this past fall (Sept. 2019). I shared the seeds with my co-worker who was ecstatic about this find. And I decided to plant some in the autumn, and another batch of them next spring. Since I didn’t know anything about growing rhubarb, especially from seeds, I planted some of each of the three varieties in the small 6-packs and another set in 6-inch/15-cm pots. They were all kept together and treated the same. I had plenty of seeds, although one was more expensive because apparently it doesn’t flower much and even then doesn’t produce that much seed, but is the most improved variety of them all. End of side story. Now here is the interesting thing. In every case, all three varieties in the 6-packs (basically 6-cm pots each cell), almost all of the seeds germinated. (The more expensive variety also didn’t have as high a germination rate as the other two, but had at least two seeds in each cell germinate.) In contrast, all of the 6-in/15-cm pots had much lower germination rates. One pot had only 5 seeds germinate, one had 4 seeds germinate, and in the pot with the expensive seed only one seed germinated. The difference in germination rates between the pots and the cells with identical watering, sun, warmth, etc. was considerable. They’ve been growing for a couple of months, and of course the ones in the 15-cm pots are now outgrowing the ones in the 6-packs, which I expected. But I didn’t think the size of the pot would have that much effect on the germination rate. So I have now also planted some of the bulb species I’ve had such trouble with over the years in 6-packs as well. We’ll see how they do this time. I don’t know the reason for the above difference. Maybe some seeds want a medium that dries out more quickly between waterings? Maybe there is more available oxygen in the soil in the smaller pots? It’s hard to say. I do know that there can be vast differences for some species in how they like and will grow in pots compared to how they grow in the open ground. (Some species hate growing in pots!) Anyway, I thought I’d throw this experience out there. My experience with rhubarb in conjunction with Dylan Hannon’s apparent ability to germinate any species from any locale anywhere on the planet that has a warmer climate in tiny pots, might mean there is something to it. I’m no expert, but there it is. --Lee Poulsen Pasadena, California, USA - USDA Zone 10a Latitude 34°N, Altitude 1150 ft/350 m > On Jan 9, 2020, at 12:13 PM, M Gastil-Buhl <gastil.buhl@gmail.com> wrote: > > Hi Uli, > > I look forward to your Bulb Garden article. Here is a photo of my mini > plunge bed trays for seed pots. I totally agree bigger pots provide not > just more moisture reservoir but also dampen the temperature highs and > lows. I am not sure my mini plunge is worth the extra effort, as I have not > tracked results precisely. My impression has been that seedlings do better. > But this is strongly biased because I only give them this advantage after > they earn it by emerging (germinating). The tiny pots are 2.25 square at > top and 3 inches tall. Each tray holds 15 tiny pots. Each spot is held open > by a lower pot, with coarse sand at the bottom. The trays have holes > drilled in their bottom and window screen between two nested trays holds > the coarse sand in. The sand stays damp a long time. Some species like to > send roots into the sand. _______________________________________________ pbs mailing list pbs@lists.pacificbulbsociety.net http://lists.pacificbulbsociety.net/cgi-bin/…