Plunge beds

[Alex]

Hi,

A quick question for those that have plunge beds (most people probably!) What do you line them with? I now have a new plunge, but it is just metal sides and a corrugated iron base, so I presume it needs lining, but with what? I have found an old thread on this forum in which plastic pond liner is mentioned. Is this the norm? Would you just make some small holes for drainage if so?

Any help welcome!

Many thanks,

Alex

[mark smyth]

nothing lines my aluminium plunge

[David Shaw]

I lined ours with old plastic sacks cut to make them into sheets. They overlap but allow seepage of water, if necessary.

[Alex]

Thanks, both. Mark, doesn't the sand leach out when you water into the plunge?

Alex

[mark smyth]

now yes because one plunge isnt very full but the two that are filled no problem so far

[Kristl Walek]

Alex,
I suppose construction of one's plunge bed depends on what it will primarily be used for.

It is my *most* important garden "tool"---something I could not live without---and the first thing I would again build when I change gardens. I have better success overwintering plants in the plunge than in cold frames. And a plunge bed is a snap to build.

I use mine primarily for overwintering plants in pots, including small first year seedlings. Also to grow on bulbous plants from seed until they are large enough to plant in the open garden. My current plunge is in full sun, on a flat site, where water does not accumulate for any extended periods of time. I would like to have another one in light shade.

It is a large rectangle, outlined with railway ties, filled with sand to a depth of about 12" (to accomodate deep pots). Not lined in any way (not sure why folks would line theirs????) Exposed to the elements. Never covered.

The only maintenance ever necessary is to top up the sand every few years (as I tend to steal it from there for other projects).

Plunging in sand is easy (although sand must be moist or else it collapses on itself when plunging).

[Maggi Young]

Woo! Kristl ... now those are plunge beds! 

Some of our psand plunges are a bit close to trees and a hedge and, even though raised above ground level, we do have a bit of bother with those roots coming up into the plungs.... so I suppose a lining underneath mighthave been a good idea.... but we give the roots a good dig out every few years and it's not that big a problem. not sure why sides would need lining either, really 

[Alex]

Thank you Kristl, that is a really excellent plunge!

I'm afraid I have caused confusion by carelessly stating bed when I meant staging in the original post - as in greenhouse staging. Apologies for my mistake, but hopefully the question makes more sense now.

Sorry again - must not have been thinking.

Alex

[Kristl Walek]

hopefully, Janis Ruksans will add to this post....because he sent me this picture of his greenhouse a couple of years ago...i believe he said his boxes were lined with styrofoam sheets on the sides---obviously for extra cold-protection in his climate---which may not be an issue for you, Alex. I can't remember if the soil in the boxes goes all the way to ground level, or if there is a "false bottom" somewhere....

[David Shaw]

I answered as for a staged plunge in the greenhouse. The outside plunges have the weed stopping membrane underneath. They are a tiny fraction of the size of Kristls'.

[Paul T]

Kristl,

How in the world do you get to pots in the middle of those large expanses.    I can just imagine spotting weeds in there and then having to work out how to clamber over the other half million pots to get to them.

I think one of these years I must do something along these lines..... getting far too hot and dry here in summer now for many things.

[Kristl Walek]

Kristl,

How in the world do you get to pots in the middle of those large expanses.    I can just imagine spotting weeds in there and then having to work out how to clamber over the other half million pots to get to them.

Ah, Paul....it's my very logical, brilliant mind and practical spirit that does it 

But truth be told, I don't ever need to get to anything in the middle....everything more or less comes out every spring and goes back in the fall.

I have already arranged them logically as to what needs to come out first (by sale times, by flowering, by stress etc). The pots that stay for the summer are in their own (shadier) sections in the rear, closer to my building, where they are easily accessed, if necessary.

I've actually arranged the plants in sections, as you will notice, with walking rows in between, so that I can get to everything if need be from one side, or the other.

When I plunge again in the fall, it is with the same forethought as to what comes out in the spring and when, and what stays.

Next week I will un-plunge the very first section of alpines and succulents that need to be tidied up & prepared for my first sale of the year, on Mothers Day and thus, I progress, until the bed is mostly empty.

Needless to say, the weeds that *do* appear, are a snap to pull out of that lovely sand. And when it is empty I routinely just rake it lightly to keep it clean (and feel very Japanese & spiritual while I am doing it 

What *is* problematic is leaving plants in the plunge for too long (years) ---with them rooting down through the pots & deeply into the sand. In the last picture, you will notice a batch of very tall plants in the left rear corner---these are seedling woody species that had to be literally excavated last fall, as their roots went several feet down.

And I forgot to say that in the summer, when the plunge is mostly empty (with the exception of seedling pots and bulbous species)--this is where the fun happens--because the sand bed then becomes the place to make free-form troughs. The sand is wet down, the shapes are made, and the hypertufa added. They are then left there to harden & cure, and lifted out when ripe. Nothing could be easier.

[Lesley Cox]

I've used weed mat and also thick old tarpaulin as a base to my plunge beds (outside) and still the roots of the damn eucalytps come up through.

[Kristl Walek]

the important lesson is to build the plunge bed as far away as possible from any woody species. mine is over my septic bed---a good use for a mostly unusable space.

[Rodger Whitlock]

A quick question for those that have plunge beds (most people probably!) What do you line them with? I now have a new plunge, but it is just metal sides and a corrugated iron base, so I presume it needs lining, but with what? I have found an old thread on this forum in which plastic pond liner is mentioned. Is this the norm? Would you just make some small holes for drainage if so?

Some 25 years ago, in preparation for building a raised bed for bulbs, I looked for guidance, and found it in the SRGC bulletin. The particular issue was, to dig out under the raised bed and put in "drainage" or not.  The advice was not to do so, regardless of your soil. If you had fast-draining soil, no need for "drainage" at all. If you had poorly drained soil, digging out underneath and putting in "drainage" would merely create a sump to hold water and keep the bed above unduly moist.

Mutatis mutandis, the same applies to plunge beds. The plunge medium (usually sand) should be in direct capillary contact with the soil underneath. If the underlying soil is reasonably well-drained, then the plunge bed can be a simple excavation filled with sand, but if poorly drained, you really should have the plunge medium above grade for drainage.

My own experience revealed that perhaps the most critical factor is making sure the walls of a raised bed should be able to resist the lateral force from the weight of the soil or sand filling it.