It is two months since planting the seeds, so time for an update: The two that sprouted are doing very well in the greenhouse and have been up-potted to one litre containers. Each new set of leaves is looking closer to the adult leaf shape. They look so healthy! The other three pots showed no signs of sprouting so I moved them to the fridge, bagged, for a cold treatment about five weeks ago. I am 99.9% sure they will be dead, as I do not think they can survive very long outside of the nutlet, but will bring them into the warm soon and give them a final chance.
Great to see you have two healthy Acer pentaphyllum M. The more of these endangered maples that are grown the better.
I think they are both alive. One is definitely alive and started leafing out from the lower trunk a couple of weeks ago in the greenhouse, and now starting to leaf out higher up. I think the other has buds swelling but no leaves yet. Will have to check the greenhouse tomorrow. Seems to be normal for one to be farther ahead than the other, the older ones are at various stages of starting to leaf out or buds swelling also. When they are leafed out properly I will add some pictures. As an aside, keeping Acer pentaphyllum in a greenhouse over the winter and spring in UK climate seems to bring leaf out forward by around two to three weeks - the older plants which used to be kept outdoors would break bud around the end of May or early June, the last two years in the greenhouse it has been mid-May. And they will be coming out of the greenhouse for the summer very soon....
Still in the greenhouse this year, I tend to keep them in till they are well into the leafout process which usually equates to earlyish May (when in the greenhouse). They are far and away the latest maples to emerge in spring (sometimes summer!) that I have grown. The 2 small ones germinated in 2022 are both alive, around a foot tall and seemingly very healthy. I will post pictures probably around June when they are fully leafed out. I know I missed pics last year but this year for sure. I also have 3 older ones which are doing well. I have not lost any of them since I started overwintering them in the greenhouse. In years previous when overwintered outside near the house I would lose the odd one every year or so. After discussion with @emery we both seem to think that it is the winter wet in the UK/Northern France that kills Acer pentaphyllum rather than the absolute cold temperatures. I have seen -10C temps not bother them and he has had ones survive to -15C, but both of us have lost plants in milder winters, presumably because of a combo of wet and fairly cold for long periods. A more general question, has anyone seen any A. pentaphyllum plants persist long term in the UK climate when planted in ground? I know I saw some small ones at Westonbirt that failed after a few years, and cannot remember ever seeing a large one at an arboretum. Given what I know about their winter survival trends when grown in pots, and that their native habitat in China is on steep mountain sides, I would suggest the hypothesis that the best prospect for in ground cultivation in the UK is in mounds or berms of well draining substrate raised 30-60cm (1-2 feet) above grade.
Here is a mature pentaphyllum, planted in St James's Park, London. Behind a Shishigashira, by the lake, and nearest to the Buckingham Palace entrance. What three words ///hulk.spine.deeply. I was able to identify it via a web page that shows the tree, link here. https://www.treesandshrubsonline.org/articles/acer/acer-pentaphyllum/ My photos attached,including two of the base which maybe help with your question about planting.
Magnificent! How tall do you estimate it to be? I will have to try and see it for myself one day. Well, that blows my theory out of the water (no pun intended) - you can't get much wetter roots than a lakeside planting. Interesting also to note that the link you posted references a pentaphyllum that is at the Ventnor Botanic Garden, Isle of Wight, known as the hottest garden in the UK. Central London is also one of the least cold parts of the UK, so we are back to cold tolerance as the likely limiting factor for long term survival.
Here are a couple of blurry images of the tree in St James's Park, London from Google Maps street view, 7 years ago.
Thanks, I had a look round on street view just now and the plantings around the lake seem to not be moisture loving plants which makes me wonder if the lake is a concrete bowl construction with little or no exchange of water with the surrounding land. I have seen concrete lake construction in other London parks but have never been to this one. I was trying to reconcile the lakeside planting of Acer pentaphyllum with what we know of its preference for extremely well drained hillside environments and the neatest solution is that it is not really a (natural) lakeside location due to the artificial method of lake construction.
Excellent, thank you, just how I thought it might be constructed. I suspect, given the location close to the Mall and Buck Palace, there is also a very robust drainage system to stop the lake overflowing in heavy rain. Yes, thanks, I had managed to spot it among the pedestrians using the What3Words "hulk.spine.deeply" posted above by @Ian Stanton and comparing the view to your street view screen cap. I am going to repot my two year old pentaphyllums soon and will post some pics at that time.
@maf , although I grew on a few of the Australian seeds I got from you years ago, I can't really remember the timing... I have a bunch of this same seed in the fridge now. Presumably you also rec'd it in our spring. Do you remember the procedure, meaning how long you left it for stratification, and what you did with it afterwards? My current crop of penta seedlings were very hit-or-miss even in the greenhouse, and the ones that lived weren't always those that appeared to be the strongest plants! Some came out even in early May, others waited for June, when they had all been brought outside. The largest/oldest one, which I kept outside, leafed quite early but the whole top died back! Go figure, a perplexing maple.
@emery the seeds I received years ago had, I believe, been sitting on the ground in Australia for months before being sent to me due to timing of swap. I am trying to remember what I did re stratification when they were fresh but I am pretty sure it was not a lot. Probably just in the fridge for a few weeks in damp media.... Scrap that, I looked it up: That was written late February 2011, so they germinated sporadically over about 3 months. Probably would have benefitted from a couple of months cold and damp stratification, but not sure. The seedlings had a really long growing season that year! However I lost all the small and weak ones the first winter and a couple more the second winter leaving about 4 left out of an original dozen seedlings. It was not a cold winter that year but was very wet in April 2012 which I imagine they did not like much. I still have 3 left of my original batch today. Since transitioning to wintering the plants in the greenhouse I have not lost a single one, and that includes the 2 recent seedlings from the old seeds. While I am thinking about it I will add a quick recap of all the things I have found beneficial through trial and error of growing Acer pentaphyllum in containers in a UK type climate. This might help others but will also be a reminder for myself: Sun, lots of direct sun in the growing season. You really cannot overdo it. Overwintering in a greenhouse, and keeping the soil on the dry side with little or no irrigation through November to end of February and only gradually increasing after that time to prevent complete drying out. By April/May, with warmer temperatures water regularly in hot/sunny weather, but be prepared to hold back in cold dull spells as there are still no leaves to transpire water. Move outside either when leafout is well underway and/or danger of frost has passed. During summer and autumn they seem to do fine on the same watering schedule as japanese maples. They seem to be healthier in unglazed terracotta pots rather than in plastic. Probably due to better moisture regulation and cycling. Leave outside as long as possible in autumn or early winter as they are very late to lose their leaves. Once any sharp frosts start they should be moved to the greenhouse, but if I can get away with leaving them out till the end of November I will.
@maf my seed was fresh-ish, certainly hadn't been outside over winter, so I've had it in the fridge. No sign of germination as of yet. In another month or so, I'll probably move them into a tray and put in the greenhouse. I also find that when there's not much sun, they resent too much water, even in my ultra-draining medium,
Sounds like a sensible plan. Another option would be to retain a few in the fridge over winter and when you are ready split open the nutlets and get the seeds out to plant "naked" - it defeats most of the factors that inhibit germination.
