in a seed bed of just sand, or two-thirds sand and one-thirds #3 grit
I was suggesting this as a layer for initial germination that is on top of a mix containing some nutrition. I've never needed to do this for any penstemons, myself. I always direct seeded into a uniform well drained mix. I would only do it if I think I will encounter a disease problem. I mentioned this method because of your wetter climate, for the westerners.
Some will transplant seedlings at the first set of true leaves. Myself, I lke to wait until 2 or three sets; I think I get better survival. Sometimes if there is only one or a few seedlings in a pot, I won't transplant until the following year.
I 've always wondered about the tube sand: what it actually is. Since it is only meant to be sold as weight for your vehicles in winter (at least here in Minnesota), is it really JUST sand, or ...? I dunno. Where does all the sand that street cleners sweep up go? I think it is safer to use the bags of sand labeled as play sand or sand for mixing with cement. Or the stuff in bulk at a landscape place. At least with these, you know for sure there won't be any winter salt contaminates.
People talk about sharp sand. The best quality of truly sharp sand is pool filter sand. Very angular, and with ABSOLUTELY no fines. I have used it, but don't see any need for it. What you do want is as coarse sand as you can find that has as little fine particles in it as possible. (That's where the "washed" sand will help.) Isn't that the same as pool filter sand? No. You're not worried about having all the exact same size aggregate that pool filter sand has. In fact you want all different sizes, minus the very fine. (That's why you add pea gravel, or other grit sizes.)
Sharp (pool filter) sand and Builder's sand
Again, at the seedling stage, what alpines grow in isn't as important. In fact, some growers purposely grow seedlings in richer soil to give them a jump start. But they always get put into the proper mix eventually.
Rick Rodich zone 4a. Annual precipitation ~24 inches
near Minneapolis, Minnesota, USA
Well, this evening I took my first halting steps into the world of sowing penstemon seed in pots. I have no idea if what I did will work but I planted seed in five of the 15 plastic pots I have, which are 7" tall and 6" in diameter. Since I only have a single bag of pea gravel, I filled the bottom half of each pot with a mixture of pea gravel and something called Hydroton, "expanded clay pebbles" that I bought at a hydroponics store. For the next layer, maybe a quarter of the total, I mixed regular potting soil and #2 chicken grit. Then for the last quarter, I mixed 50% turface and 50% sand and added that. I then planted the seeds directly on top of that, covering the seeds gently with a sprinkling of that mix. Tomorrow I'll water what's in the pots and place them outside.
I planted Penstemon albertinus, ovatus, richardsonii, grandiflorus and cobaea.
I'm not sure I have the patience to germinate the seed in one container and then transplant the seedlings into another.
Any thoughts about whether what I did has some chance of working? If not, I have 10 more pots in which to make even more interesting mistakes.
Near Boston, MA, zone 6b. Average annual rainfall = 44 inches
When I plant seed, especially from seed exchanges, most of the time I use 3 or 4 inch pots. It's not uncommon that seed doesn't come up (for a variety of reasons), but sometimes I will get a plethora, and sometimes just 1 to three. If I just have a few, they might stay in the pot untill the following spring when I transplant. With bigger pots, you just need to be more careful about overwatering.
I may have confused you when I explained my layering with my townsendia seeds. Layering of different types of soils and especial vastly different size aggregates can be problematic for plant growth, if you are expecting roots to cross over into adjacent layers. Unless a layer is "better" than the layer a root is currently in, the root just won't go there. On the other hand, a gradual change over of one kind of soil/aggregate size to another is perfectly fine. Roots have no problem penetrating to whatever depth is healthy for them.
Almost all rock and alpine plants like their "necks" very well drained, with roots penetrating deeper into moister soils. The crown of the plant (the neck) is susceptible to rot, whereas plants native to moister climates without dry winds have adapted to become rot resistant. This is why rock and alpine gardens don't use an organic mulch (like leaves or barks) that retains moisture at the surface. Rather, rock gardens have rock mulches that dry out quickly. So this was the exact reason why I modified my townsendia seeding: to keep the susceptible crown of the plant (where the seed is) dry, while still allowing the roots to grow down to where they can obtain moisture and nutrients.
Notice too, that my townsendia example is exactly the opposite of yours. Mine is larger aggregates on top, with smaller aggregates below. This is how nature works, too. You have small aggregates on top, with large aggregates below.
So what I would recommend is mix all those ingredients together at approximatedly the same ratios as you have stated (it's not rocket science), and fill the pots with the same stuff, top to bottom. It's going to be very rocky; your penstemon will love it! If you would like to still have a few millimeters of sand on top or a top dressing of grit, that would be fine.
By the way, Penstemon hirsutus var. pygmaeus is a stalwart rock garden plant, and a blooming machine. Being the species hirsutus, it's already adapted to the east and will do great with no special care in your climate.
ok, thanks for this. I did misunderstand so I'll just start over on those five pots and mix everything together rather than layering.
btw, I notice that in his book Growing Penstemons Dale Lindgren recommends for a potting mix just perlite and vermiculite, with the possible addition of sand. In his book Robert Nold suggests something similar: "equal parts perlite, vermiculite, and sand," mentioning later in the paragraph that grit is good as well.
I was surprised at their focus on perlite/vermiculite; I haven't used those at all except the small amounts that's already in the 20% potting mix I used. Maybe since I'm in a much more moist environment perlite/vermiculite is less necessary?
Thanks for the tip about Penstemon hirsutus var. pygmaeus.
I would have redone those first five pots if I had not already seeded them. How are you going to retrieve the seeds? It's your call ....
Maybe since I'm in a much more moist environment perlite/vermiculite is less necessary?
Actually just the opposite: the perlite and vermiculite provide more air spaces in the growing media (while not adding nutrients). This becomes more important in place with higher rainfall and more humidity. Think about how much more dry a western soil is, compared to yours in Massachusetts.
Bob Nold understands soil physics better than most!
Regarding P. hirsutus var. pygmaeus, the seed is always available in our seed exchange. Because it is a seed grown dwarf, you may find size variation in the seedlings. you might want to discard the largest, fastest growing one(s) if you want the keep your stock the most dwarf.
I did redo those first five pots. My plan was to take a spatula and scrape off the first inch of mix at the top of the pot and put that in another pot, then mix everything up, then put the inch back on at the top. But I didn't. I just mixed everything up - seeds at the top and all - and then put fresh new seed at the top. Thank you to seed exchanges for making that possible.
Maybe 20 years from now the old buried seed will make its way to the top and surprise the heck out of me and germinate.
Thanks for the thoughts about perlite and vermiculite.
btw, why is there a danger of overwatering with large pots? I did use the 6" pots.
Here are the penstemon species I planted:
...with (I think) many more to come.
That's quite a list!
It's easy to overwater large pots because they hold a lot more water and take longer to dry out. People have these unfounded tendenciesto kill plants with love (and extra water), and put watering on a schedule. Both are never good things. If you only water when they need it, you will do fine. Just don't water every Sunday or somesuch. Timing will change according to many variables, and of course, seeds actually use very little water.
I am wondering if it would be good to put some window screening over my pots outside, to keep the seeds from blowing away and maybe keep critters and birds away from the seeds as well as the seedlings once they emerge. Is some kind of covering that like standard protocol for pots of seeds left outside in the winter? I have a large roll of window screen which I could cut into pieces, but I'm not sure how I'd anchor it around the top of the pots. Maybe some thin wire.
RickR, I want to thank you for the help with this back in February and give you an update for this batch of seeds I started in large pots. (This is separate from the seeds I started in milk jugs and potting soil that I just posted about.) For this batch, I used a mixture pretty similar to what you'd suggested: pea gravel, chicken grit, turface, sand, and a touch of seed starting mix. I'm pretty happy with the results so far. They're all growing very slowly, and I still have only cotyledons, and for some species I have only one or two seedlings in the pot, but it's a start. I have: P. fruticosus, P. virens (many seedlings), P. grandiflorus, a P. strictus x P. barbatus hybrid (many), P. gormanii (many), P. richardsonii, P. ovatus, P. cardwellii, P. digitalis, P. venustus, P. tenuis, P. virgatus, P. newberryi, P. albidus, P. rupicola, P. eatonii, P. superbus. Hopefully soon I'll get some true leaves, and then who knows what time will bring.