Pumice pebbles to potting soil ratio for Japanese Hollies?
DahliaDiva
Posts: 12
Greetings Gardeners, I am a longtime lurker who finally joined in order to ask a question I couldn't find among your excellent discussions.
I've read that adding pumice to
soil helps aerate it w/o it breaking down like perlite. But what is the proper pumice pebbles to soil ratio? 20%? 25%
For context, I'm planting Japanese hollies in pots that are 56cm wide x 48cm tall. The hollies are just over 2 ft tall and will get up to 4 ft. I'm in the Pacific Northwest of the US (Oregon), where we have very wet winters and hot, dry summers.
Full disclosure, I thought I had bought bags of
MiracleGro organic potting mix, but in fact, got their raised bed soil mix (which has earthworm castings, bone meal, kelp meal, compost etc). Can I salvage this as potting soil by adding pumice?
Many thanks for any advice.
Posts
If the pumice can be used in the same way as the grit/gravel, the ratio wouldn't be too important, but a 2:1 soil/pumice would probably be fine, or even 3:1. The bigger problem will be ensuring the moisture in your summers, but I expect you're fairly used to watering anything through those months. You can also keep the plants in a shadier site for those months, which will help.
The only other thing I'd say is - the pots seem a bit big at this stage, if the shrubs are only a couple of feet. You could pot them into bigger pots to grow on this year, but submerge those in your 'fancy' ones until they've grown a bit more. They'd be fine in drier weather, but you might find they'd struggle a bit in the wet winter if there's too much wet soil around them. It's different when plants are in the ground, especially when planted in spring, as they can adapt better, and there's usually other planting to help with taking up moisture in winter. Not so easy when potted. Just something to consider perhaps. Hope that's of some use!
I live in west central Scotland - not where that photo is...
Hi Fairygirl, Thank you so much for the reply. It's kind of you to take the time. I've been following Monty Don's advice of mixing grit into soil (referred to as “turkey grit” here in the US). Pumice appears to be used similarly, but is much lighter weight (which my back appreciates). It also stores tiny bits of water and makes it available to plants w/o drowning the soil. Apparently pumice is also found on the beaches of the Western Isles of Scotland and Orkney and Shetland. This link has some good info about pumice: https://www.plantisuss.com/post/pumice
You make a great point about the pot size. I'd normally pot up by only a couple inches. I chose these pots because the plants were rootbound in 3-gallon pots, but miraculously healthy. The nursery owner confessed that they should have been potted on ages ago and would have been full-sized by now in bigger pots. He offered 3 hollies for less than I would've paid for one plant that size. How could I resist a bargain like that?
Also, I found an article in “The Spruce” (about potted Japanese hollies) that said, “Choose a container that is at least 8 inches wider than the root ball of the plant to give the shrub room to grow for the next two to three years before repotting the plant to a bigger container.” That's a much larger gap than the normal 1 or 2 inch recommendation, but about right for my situation. Japanese hollies are quite hardy here, so fingers crossed.
Many thanks, Dhttps://gardentabs.com/vermiculite-vs-perlite-vs-pumice/
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
I doubt it would be harvested here @imnotyourdata - due to the possible [probable] damage to the environment, but I'll have to have a look around the t'interweb to find out about that, now you've mentioned it. Our north western hills in Scotland have a very unique geology, especially in Assynt, which is why they look the way they do. A mix of billions of years old Lewisian gneiss and sandstone.
https://www.geolsoc.org.uk/GeositesAssyntMountains
They're a good size then - your plants, if they're in 3 gallon pots. That's the equivalent of a builders' bucket here, so you should be fine with your intended pots. Just be sure the roots aren't completely stuck - you might need to do a bit of teasing out to ensure they spread well. A great bargain indeed
I think it'll just come down to whatever is easier and cheaper for you to buy. The weight will be a factor for you, especially if you want to move the pots at any point. I can understand that.
Good luck with them - I hope they do well for you. You can upload photos of their progress if you want - the icon that looks like a hill is the one for that. Keep them on the smaller side if you can as there's an ongoing problem with sizing.
I live in west central Scotland - not where that photo is...
Thank you for the article @Dovefromabove . It was very useful. It also addressed the ratio question (confirming advice from @Fairygirl ). I go thru a lot of vermiculite & perlite in my propagation efforts, but went with pumice for these big pots in hopes that its longevity might work in my favor. I added a couple inches of the pumice pebbles as mulch/weed suppressant instead of the heavier grit, since the pumice was at hand. In my experience grit has not blown away in the wind. I guess I'll find out whether the lighter-weight pumice weathers windy weather.
@Fairygirl I did indeed tease the roots on the compacted rootballs. In fact, they got the full spa treatment (with stone & watsu massage
). Btw, I finally measured these hollies. I had guessed they were a couple feet, but are actually 30 inches x 30 inches, so now I'm wondering if I'll need to repot them again.