Raised Sand (Plunge) bed preparation - examples?

petershaw · July 17, 2023, 07:45:29 AM

I have been looking for a great way to keep my growing collection in a single space to have good sunlight in the winter/early spring and hot but protected summer temperatures.

Have read a few of you have these sorts of beds and having seen the beautiful Alpine beds at the Royal BG Edinburgh and Wisley I think this might be an option.

I have come across some 2x12 fir boards that I can use to make some nice raised beds (waist height for viewing and I don't bend very well anymore). I know they will rot reasonably quickly so I think I will want to add a liner.

I have built several aquaponic systems and ponds so I know how to make them water proof but I am now thinking about drainage.

I'll need lots of holes, and bulkhead fittings are a bit expensive, so I think maybe creating a series of sloped areas like a shower base might direct the water out quickly. Maybe use some of the tile set material under the liner.

Water does not move well from sand to gravel so that is not really a good option, and I have never used sand in a pond so I am not sure how to keep it in the base without it falling or clogging.

I can make it pretty deep so maybe the sand to gravel and perch layer will not be an issue.

Any suggestions or comments?

Peter

janemcgary · July 17, 2023, 04:35:23 PM

I grow my bulb collection mainly in plunge beds, but they are based directly on the ground, so I do have to bend over to tend them. I think Peter is talking about a kind of deep table with space below it, a setup I saw at the nursery of bulb specialist Walter Blom. Walter's construction had simple covers to limit the amount of rainwater getting to them. I don't recommend using wood if any alternative is possible. Now I have concrete block surrounds. My old bulb frames were surrounded by railroad ties (British, sleepers), which last for some years if in good shape to start with. Now my bulbs are in a kind of greenhouse with a solid roof and open sides. As for drainage, woven commercial nursery groundcloth permits it. I think the plunge (coarse sand, here) should be at least 16 inches/40 cm deep to allow the larger pots to be plunged almost to the rim. If the table design is used, there are strong plastic grids available (here, for tables in commercial greenhouses) that could be topped with woven groundcloth; I use them for shelves holding flats of plants. Hope this helps.

CG100 · July 18, 2023, 11:52:49 AM

I have never built, or contemplated building, a raised sand bed.

Bear in mind (forgive pun), that one cubic yard of sand (which could include your pots if you use high mineral composts) weighs a ton and a quarter when dry and around one and half when damp.
3 foot wide bed, 9 inches deep, 12 feet long, that is one cubic yard. (9 inches isn't very deep for a sand plunge.)

Not only must the bed itself take that weight, but any frame underneath, and any footings/foundations for that frame has to, too.

Uli · July 18, 2023, 04:30:51 PM

Hello Peter,
There is one point I do not understand in this thread. Is your intention to build a raised bed with the sand plunge in contact to the ground or is it like Jane thinks a deep table with space underneath?

I think the table type with space underneath is not a good option, certainly not if built from wood.

But a classic raised bed standing on the ground might work very well. From bitter experience I recommend to build it rodent proof to stop rodents coming in from below. If you want to use a liner to protect the wood in a raised bed, why not put the liner on the vertical board walls only and leave the bottom unlined except for a metal grid to keep the rodents out.

Bye for now

Uli

CG100 · July 19, 2023, 04:11:21 AM

All of the raised sand plunges that I have ever seen have been "boxes" of sand, on legs - just like a standard greenhouse bench, sort of. I have never made note of construction as I have never contemplated building or buying one.

Just forming a raised bed on the ground would have lots of problems, not least, plants rooting through, outside of the pot. You also could not really control the moisture content of the sand.

I don't know what is available here on the PBS site, but if you can't find anything, there are many, many pic's of Iain Young's raised/plunge and other beds over on SRGC and Iain himself is more than helpful. The same probably applies to the AGS as sand plunges are very very popular amongst alpine ethusiasts.

Looking at off-the-shelf options here in the UK, they are basically small, so that the wieght isn't great when full.

Making timber ones shouldn't be so bad, except that the base would need to be very thick and very well-supported. The sand should mostly be dry, and certainly never be really wet.

illahe · July 19, 2023, 08:39:41 AM

Hi Peter,

I recently added on to an existing raised bed to make a plunge, It's 3-2x12" tall. I do second a few of the previous suggestions, mine is solid mostly because i'm in a frost pocket and a table would allow cold air underneath in the winter. The base soil is my old potting mix, which is mostly pumice and decomposed organic matter that drains very well and I haven't had any issues with a perched water table. The top 18" is sand. I've only had one drainage issue and that was following multiple days of hard freezing followed by heavy rains, until the frozen layer thawed out there was some standing water. This was in the late winter early spring season when everything in the frame seemed to appreciate it, but it did make me scratch my head for some ideas to solve the problem. I will be adding a cover to make this a true alpine frame before next winter.

The design was very simple, butt joints with long lag screws and I also added some galvanized corner reinforcement, and 2x4's down the sides for reinforcement, at the very bottom is a permeable ground cloth to keep rodents out. It's really just a big box. Currently what they sell as pressure treated wood doesn't last very long at all, so I think your idea of a liner is a good one, but trapping water against an impermeable still could lead to rot. Lately I've been thinking about a simple plunge bed for putting into an existing alpine house and I think I would go buy one of those galvanized water feeder troughs they have at the farm stores, drill drainage holes and fill it with sand.

Mark Dryas octopetala-1.jpg

Uli · July 19, 2023, 11:10:16 PM

There are now ,,boards" made of recycled plastic. I have used them in the past in my former garden in Germany with excellent results to contain my compost pile. And I have seen the same material here in Portugal for sale, including fence posts. It is heavier than wood but can be worked the same way. And the material is strong and solid. It is of grayish brown muddy color so fits well in the garden. It is maintenance free and should last for a long time.

CG100 · July 20, 2023, 01:14:52 PM

The problem with plastic is that it has no intrinsic strength - apply a modest one-sided force over protracted periods and it warps/creeps.
For reliable long term use, it would need to be fibre-reinforced.

In Europe you also have the hassle that there is nothing that is generally available as a wood treatment that actually lasts. Wood treatments here are now cypermethrin and not much else. Creosote is atill available, but you need a permit/licence.

David Pilling · July 21, 2023, 03:08:34 AM

Quote from: CG100 on July 20, 2023, 01:14:52 PMCreosote is atill available,

We had a discussion of materials previously:

https://www.pacificbulbsociety.org/pbsforum/index.php?topic=592.0

People do have raised beds that are enviable - but like Ian Young growing bulbs - there may be a knack.

petershaw · July 23, 2023, 07:15:57 AM

Hi All,
thanks for the comments and suggestions.

I don't like gardening in the ground, it hurts my busted up back and my career has been teaching how to grow greenhouse and landscape plants in containers (and food in water).

I am also looking for a way to add beauty to the landscape and avoid having to move plants around every season.

Maybe I am naive that I can grow winter bulbs in place and have them go dormant while still being attractive.
I may add a removal top (cold frame style) and a shelf above it so I have have some other plants looking nice during the summer.

I am not worried about the weight of a free standing box. I have lots of 1 -1/2" square tubing and decent welding skills to build a raised bed. (Painted with rust encapsulating paint.)

I still have to run this past the boss though the backyard is sort of mine.

I have built a backyard aquaponics system, a 9x12' greenhouse out of square tubing and double walled acrylic, wicking beds for veggies among other enhancements.

MarcR · July 23, 2023, 05:34:12 PM

Peter,

I find that using a mix of sand and gravel is free draining and makes a better transition to gravel. Loam or pumice or topsoil can be added to meet the needs of individual species when used as a potting mix.

OrchardB · July 24, 2023, 01:52:04 AM

I have built plunge beds in the past with angle iron legs and frame (fence posts) and 1" thick timber (ply or planks) bottom and sides. Then lined with heavy polythene or pond liner. Length needs to be limited to prevent "bowing" or use cross struts.

Arnold · July 24, 2023, 07:12:13 AM

I had a plunge bed built years ago with stainless steel. I went to a place that does stainless steel products for kitchens.

Its 3 x 7 feet six inches high, lip on top if folded over to prevent scarping and cutting my hands as I reach in. Put a drain spout on the lower part on one end in case I had to drain water out. Filled with a combination of gravel and sand. All kinds of things have popped in in it. The Othonnas seem to like it best.

gastil · November 26, 2023, 07:56:49 AM

Here are a couple of my sand plunge beds. Years ago, these were tidy and worthy of a shared photo. Today these are an example of garden entropy. The sand settles, exposing the sides of pots. And until I re-build the critter netting, random bits of wire mesh protect pots from scrub jays planting acorns. One bed is wood and is holding up well after 12 years. One bed is plastic fake-boards. A cut-off piece is visible sticking up vertically to shade the side of a pot. Unless the pots are neck-deep in the sand, they can get too warm exposed to the sun.

The square box has soil moisture and temperature sensors buried in the sand. As expected, the sand temperature a few inches down is significantly damped in diurnal amplitude compared to air temperature measured by the weather station atop that steel pole.

I use a very coarse sand, the most coarse available here, sold for sand blasting. It takes a lot of time and effort to wash the dust out of it. And it does not hold shape unless saturated. It is the same sand I use in my growing media.

janethffnn · November 26, 2023, 05:18:54 PM

Sorry that it took this long to get to the forum and post my photos. I have attached photos of my bed here. I actually made it with parts of an old L shaped raised planter that I made lower and reconfigured as a square. Looks like it was a topic that attracted quite a bit of interest. I like seeing what others have done.