Wicking bed in greenhouse.

I'm adding another greenhouse to my property. I have always thought it was such a waste to have all the run off not be harvested off of the exterior film. My current design will have a raised bed running the entire perimeter of the green house. The bed will be five feet wide and it will be a wicking bed. The bed will be 3 feet tall, 5 foot wide. 2 feet outside and 3 feet inside the greenhouse.  10-12 inches of the bed will be the reservoir. In the hot months I can fill the reservoir as needed. The reservoir will create a heat sink/storage. If I set the outside beds up as a cold frame, the venting can come from the top and I can still go out and open them up to collect precipitation.

Would it be worthwhile using say, IBC units, rather than a single large tank?
The concept of watering from the roof is neat!
But would using a gutter and having the whole of the bed inside the greenhouse work better for the plants?

John where I am there is quite  bit of snow. My thought is that snow would accumulate in the perimeter bed and load the reservoir. Overflow drains would water beds in the greenhouse. My most successful greenhouse to date has been one that had three rows, three foot wide beds 3 feet tall around the perimeter and were inside the greenhouse.  They weren't self watering but they had duct work that sucked hot air from the ceiling and piped it through the beds exhausting outside. My new design using the outer portion of the bed as a cold frame would be a bonus for hardening off plants or even seed starting plants that wouldn't need to be in the greenhouse. Gutters just don't survive the snow loads here.  One other thing that  have started to do inside and outside is down that center row of the picture you see pvc pipes that are the legs of hog wire tables I pant my squash or mellons and let them crawl up to the table and then plant more sensitive plants that can't take the sun underneath. The squash fruit dangle down and don't interfere with the plants underneath.

Cool design.
Without insulation,  solar gain that makes into the beds will not stick around.
What if you made the bed from scrap refrigerators, laying side by side?
They could be plumbed together or kept separate.
Ive created a  wicking bed from a fridge, it was very straight forward .
You might even be able to utilize the doors.
Chest freezers might suit your needs even better.

I think that raised beds have proven themselves to be heat sinks in most cases. Warm up faster than an in ground bed. I want to try the continuity of a single reservoir. I could and may consider insulation later but my greenhouse pictured had no insulation and essentially worked as a sunken greenhouse with that mass of raised beds around the perimeter. I could plumb in a method to solar heat the reservoir water later down the line but not a priority feature in the initial construction. Other than the plumbing that would have to be in the initial construction insulation would be a simple add on. The duct work described in the greenhouse photo post would be easily incorporated as I fill the beds, and wouldn't need to be hooked up at first either. A phased experiment with those options as it is put into service.

@Robert
My plan has been to try a GAHT style system in insulated raised beds, to avoid digging and decouple from the relatively cold earth.
That an above ground air to earth greenhouse system works without insulation is great news.

Is your system geared towards daily or annual heat storage?

Talking about the greenhouse pictured, I had 4 inch (100 mil) tubing running to the greenhouse apex. The duct work had three courses mid way layed up in the bed. The beds did settle, so the duct work did end up about 1/3 up in the bed.  I used 12 volt inline marine bilge fans on a thermal switch set @80 degrees F. The fans worked year round and used the raised beds as a heat sink/battery. Would insulation  help, yes I think it would . It doesn't take too long for the apex heat to attain 80 degrees even in the winter if the sun is out. Being in the high desert I have some radical temp swings 28 degrees this morning and 80 this afternoon. I maintained ambient air temp readings but now wish I had kept bed temp readings as well.  Being able to charge that mass makes a big difference for year round production. It is not unusual to have a freeze in the first week of August. A ground tube greenhouse would be something I'd like to play with, so little time with what I already have on my plate. My sister has moved near us and she wants a greenhouse maybe we can incorporate GAHT in that design.

I'm a big fan of wicking beds, I have several iterations. Bucket gardening  ("Gardening with Leon" on YouTube) has been successful for me and allows moving the plant around. The raised beds in the pictured greenhouse were a definite success Adding the water harvesting and wicking feature will hopefully help in the future if I have another extremely hot summer like this year.  I'll keep better track of both ambient and bed temps in the new greenhouse and add bed temp probes in the existing greenhouse.    We have been under extreme restrictions for using chainsaws due to the forest fires that have plagued us this year. It's cooled down and we have had a bit of rain, so those restrictions have been lifted. I'm clearing the spot this weekend.

I'm looking forward to seeing your build.
Digging  down below the frost line and/or insulating the air heated mass from the rest of the earth makes GAHT hard to implement for some of us.
Rocky ground and/or the expense of digging machinery and appropriate insulation can be impediments.
If doing it in uninsulated raised beds works for you in zone 4, it should work as well or better here in zone 6.

The wicking beds, what kind of liner are you going to use?
What kind of wicking medium?
I use  cut down upside down buckets to create voids in my wicking reservoirs, what are you using in your buckets?
With part of the beds outside, any thought to planting climbing shade plants for the summer months?

In my area there is 75-100 mil of pine duff and then probably  5 meters of pumice, digging is no issue. You really need to supplement the soil for water retention and nutrients. We're also a golf tourist destination area and I have access to pond liner material. I'll be lining the beds with that.  In my buckets I use milk jugs. I have used corrugated drain pipe in larger beds.  Once the beds are in place I'll hopefully scrounged up something to create the void without having to purchase something. If I have to it will be the corrugated drainpipe. It's extremely useful for greywater distribution and I'd like to expand what I have so I will need some any way. This year I experimented with Chinese yam or air potato as a possible shade plant, it grew extremely well inside the greenhouse. I'm not sure that it's the right plant for what I hoped would be a progressive  shade provider. If I were to use an outside shade plant, I have a hop variety that just goes crazy and is relatively drought tolerant. I thought about sun chokes but they are water hogs. The wife's been fiddling with hollyhocks trying to hybridize something new, they actually are pretty drought tolerant and at 8-10 feet tall can create a good screen.  I's probably going to be a combination of trials to figure out what works best.

I'm doing some research into wicking beds for my new polytunnel and wonder whether you built your inside/outside bed Robert? My tunnel will be built into the hillside a little, and I'm thinking of harvesting the water on the uphill side, running it into a wicking bed then overflowing into the rest of the tunnel in ground beds...

Things that concern me:

1: the water level in the wicking bed reservoir, as I understand it, is into the level of the soil above, so will that be permanently wet and go anaerobic?

2: The soil in the bed is said to need completely replacing every few years. This doesn't sound very healthy growing conditions to me. Can it be made big enough volume, with on top mulching to replenish nutrients, and crop rotation, to keep the soil healthy?

3: Does it really need a membrane between the reservoir rocks and the soil?

4: Is it going to be worth the effort to build a raised bed like this compared to just a normal bed at ground level? I will need to find retaining materials for the wall and a waterproof liner....

5: Is the size of the gravel in the base critical? I'm thinking of just using broken rock from the polytunnel site excavation.


I quite like the idea of the water reservoir acting as a thermal store smoothing out day and night time temperatures, and it also ought to make watering a whole lot less effort.

Hi,

I'm planning to build 3 little Wicking beds (3 x 5 m²) in an old concrete swimming pool that I would like to turn into a climatic-greenhouse .
Where I live in France, the ground water level is getting high during some months in winter. Since the pool is 1 meter deep, breaking the concrete would bring a lot of water in winter. That's why Winking bed seemed to be a good solution.

The way I had understood it :

1: They should be a hole allowing to dry the réservoir some times, for instance at wintertime when evapotranspiration of the plants is low.
What about adding some Effective Microorganisms to the water to avoid some adverse anaerobic pullulation ?

2: I had not heard that there is to replace the soil every few years. Do you know where this information is coming from ? As you suggest, I thing that the size of the bed could allow to bring life to it and keep it over the years.

3: The membrane appears important not to bring mud into the stones that could bring to an obstruction of the drainage. Even if I'm not a big fan of this "geotextile". I'm asking myself how long it is going to last !

4: It is a big question for me, and if I saw an other option in my situation I would prefer an easier solution for sure...

5: I heard of 20 cm, but in your case I would ask if the type of rock you have is fine enough. If there is to much room, isn't the soil going to push through the membrane over years ?

Sorry Nancy, I'm late with a reply,
I have beds where I have corrugated plastic French tile tubing over the top of that I placed weed barrier to prevent dirt fines from plugging them. Some of that infiltration type tubing has a permeable membrane already on it to prevent clogging.  I have three of these beds made from horse troughs and that 4 in height tubing is the depth of the reservoir. I do place a drain hole about ten inches high to bleed off any excess water that accumulates from over watering or rain. So a saturated soil is never higher than the weep hole. Protecting the voids for water would be the only reason for a permeable membrane between rocks and soil. You would want that membrane to go at some point all the way to the bottom of the planter so it can wick into the soil. Gravel or rubble size is not critical. Creating the void to hold water is what you want.
Roland,
If you will be using the pool and want to use the rise in groundwater to fill the bed maybe drill holes partially up the sides a rise in groundwater would fill the undrilled portion of the reservoir. In summer the drain holes would prevent overfilling.  Depending on the thickness of the concrete. The pool probably has a drain of some kind already? The membrane keeps the voids free of dirt.

I've got an idea of how I might do a wicking bed in my situation (new thread here). I'm thinking of using sheep fleece instead of weed membrane as wick and barrier combined. As that degrades it should slowly feed the plants too.

Roland. It seems a pity to make a hole in your pool for the ground water to come in...particularly if the water level is likely to be higher in winter (when you don't need the extra water perhaps). I think you need to be able to control the water level to be below the soil level in the beds if at all possible to avoid anaerobic conditions. Is there a lower place on your site where the water could drain to?
Adding Effective Microoganisms to the water is an interesting idea. I have heard of adding nutrients to feed the plants. If you try this please let us know what results you get!

"Gardening with Leon" on you tube shows small wicking beds made of tubs and his recipe for the fertilizer that he puts into the container. It's worth a look.