Plants in the Alpine House or Cold Frame: Plunge beds
Started by: Helen JohnstoneGo to latest contribution by Tony Lewis, 20 May 2015, 15:39. Go to bottom of this page.
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A silly question perhaps but what sort of sand should I get for a plunge bed? Somewhere at the back of my mind I think I need to avoid lime but how do I know what bags of sand have lime?
"Sharp sand" is the stuff to go for, Helen. None of the sand that builders sell should really contain lime, though. "builders sand" tends to be finer, with smaller particles which can tend to compact too much in a plunge. 'Sharp sand ' has a coarser, grittier texture and can also be used to add to potting compost which makes it useful to have around.
No need to go to the added expense of "horticultural sand" - that's just an excuse for the seller to bump up the price for sharp sand!
Get as good a depth of sand as you can manage - this keeps a more stable temperature around the pots and makes the watering easier.
I'll bet you will be impressed with how well pot-grown plants will respond to life in a sand plunge - whether that is outside or under glass.
Thanks Margaret and thanks for dispelling the myth that horticultural sand is special! I have ordered some plunge staging from Two West for my greenhouse which hopefully will arrive soon.
Helen did you line your plunge benches with polythene sheeting or similar material? The reason being if you intend to feed your plants with plant food containing cooper or other metal compounds, it could damage the aluminium. I have two west & Elliott staging in my alpine house and after a very short time I noticed little holes appearing in the walls of the staging. I had no idea at the time what could have caused this problem.
i have recently purchased another alpine house made of ceder. Not wanting to spoil the look of the house I was going to opt for wooden staging, however when the plans came back the staging would not have been cost effective in the long term. It would also have taken up to much space and I would have lost four inches at every join. I went back to two west for advice and was told the problems with the cooper causing salts which attack the surface causing pitting. We discussed coating the plunges to help with this problem. So this is what I've opted for and the staging being coated burnt chocolate blends in nicely with the wood. I'm still going to line them though I'm a very belt and braces type of girl. Three tons of wased grit sand arriving tomorrow to fill it.
Steven putting the staging together over the weekend!
Those are very smart and thank you for the advice. I am starting in a very small scale but if I expand I will follow your example. I love your middle display table although I thought it was a snooker table until I opened the picture
Just a note to say that what Maggi rightly calls sharp sand is often sold by builders merchants as 'concreting sand'. As she says you do not want builders sand. Make sure there is no cement in it!
Anne. I note your suggestion to line these modular aluminium plunge units with polythene to guard against corrosion. I was also wondering if it was usual custom and practice to try to make these units water-tight by using polythene or a similar liner ? Or is it better to allow excess water to seep out to avoid the danger of over-watering ?
We have recently completed a refit of our glassouses with new plunge staging. The first stage of this project was shown in this issue of Ian's Bulb Log : http://www.srgc.org.uk/logs/logdir/2013Jul311375281392BULB_LOG_3113.pdf - you will see that we did not line the trays againset corrosion ( perhaps a big mistake!) and we have added drainage exits to each tray in the upper run, which allows excess water to drain to a container. Hope that is of interest and help to you.
I've had Two Wests plunges in use for a number of years and have not had any corrosion issues. They are not lined but have drainage holes drilled in the bottom to remove excess water and a layer of Two West's water matting in the bottom so the sand doesn't get washed out through the drain holes.
James in answer to your question, I think most people would add drainage, alpines must have good drainage. The first frames I had I didn't line but as mentioned before they corroded. lineing these new ones is a precautionery measure but in doing so they are now water tight. I think they will be fine with carefull watering but time will tell.
Martin I think you have just been lucky with yours but maybe you live in a soft water area whether this makes a diference I dont know. Two Wests are aware of the coroding as they have had a number of people come back to them with the same problem. they now issue a warning about the corrosion issue and surgest lineing with polythene or similar. As well as having the frames powder coated we used a damp course polythene liner.
If you are getting very localised perforation of the aluminium, it suggests a local high concentration of the corrosive element, maybe, but not necessarily copper. Very sharp gritty sand, i.e. with lots of sharp points touching the raw aluminium, will create corrosion where those points touch. Any cushion, waterproof or not, may lessen the number of "points" and help. I used for many years a cheap pond liner material to protect wood plunge beds, but waterproof liners only work well if in good condition. A perforated liner will hold water against the aluminium quite well too and may make it locally worse. Painting or coating is better; until it gets scratched.
Incidentally soft water is more corrosive than hard water in general as it may be more acid. Avoid copper and brass fittings if you are plumbing in a water system to water your aluminium plunge beds. Plastic fittings are much better from the corrosion point of view.