Watering Greenhouse Plants / Staging

I posted two topics in the Spring:

Capillary Matting:
http://gardenerscorner.co.uk/forum/threads/capillary-matting.42709/

Ebb and Flood Irrigation:

http://gardenerscorner.co.uk/forum/threads/ebb-and-flood-irrigation.41890/


in the end I opted for Capillary Matting because it was quicker to install and I was overloaded by the amount of plant-raising I had taken on this year.

I'm pleased with how it has worked ... but I'm now thinking of Stage 2 - or "rethinking" might be a better phrase.

My staging is a material like Weld Mesh on a Dexion (slotted angle iron) frame. For the capillary matting I wanted a "flat" surface, so that the matting didn't dip and leave areas where the base of the pot was not in good contact with the matting. So I covered the bench with various sheets of polycarbonate and rigid perspex that I had lying around. I put the capillary matting straight onto that.

#1 improvement: cover the joints in the sheeting (including butt-joints between staging units) with an opened-up compost bag, or similar plastic sheet. All my joints drip when I get plenty of water on the matting, which wastes some water.

I covered the capillary matting with micro-pore black plastic sheet. This has enough minute holes for the capillary action still to work, but supposedly keeps the algae and spilt soil off the matting, reduces direct evaporation, and makes it last longer. There is no algae growth on the [covered] matting as a result. This does indeed work, but the roots still grow through into the matting, so are "damaged" when the pots are removed, and I have weed seeds that have blown in, between the pots, and germinated and grown just sitting on the micropore plastic!

To make a water reservoir I attached downpipe to the front of the bench, a 90-degree bend (turned upwards) on each end, and then slots periodically along the top of its length [but not continuous, otherwise the pipe would just snap-shut!]. The edge of the capillary matting is tucked into the slots in the downpipe and I fill this up with water as the "reservoir" - it means that the longest "reach" for the capillary matting is about 4', and the maximum lift is only a few inches.

The area of capillary matting is about 9-10 sq.m. and the pipe holds about 20 Litres of water; I fill it morning and evening; the pipe is always bone dry by refill-time, although the matting is still wet.

I also water the matting - I aim the watering can spout between the pots on the bench to "flow" the water between them, and towards the back of the bench. In particular the corners (the bench/matting'downpipe is continuous around both sides and the back of the greenhouse, the matting in the furthest corners has the least connection to the downpipe-water-reservoir). So I put 10L on the matting and 10L - 20L [depending on whether I can be bothered to fill the watering can a third time!!] into the reservoir, twice each day.

I make that 40L - 60L a day on 10 sq.m. of matting, so 5L/sq.m. of pots. Seems like quite a lot to me?

#2 To make 100% sure that all plants ARE getting water from the matting I water the whole bench from above using a hose and "gun" periodically - once a week perhaps, but also when I put a lot of new plants on the bench which might not have compost wet enough to start the capillary action.

#3 If the capillary matting dries out (hasn't really happened yet, but I do get the impression that the back edges have got dry-ish at times) I think it would be quiet hard to re-wet it under the pots, but probably soaking it and the pops from above with the hose/gun would do the trick.

#4 So I am doing some top-watering, and thus I do have some moss growing in the tops of some pots :(

#5 Its 1M% better than hand watering the individual pots though, so I am contemplating how to mimic this for all the plants I have standing outside "coming on" for Autumn (this year AND next :( ) planting

#6a I'm not sure that the downpipe reservoir is needed. I am of the opinion that a full blown tank at one end of the bench would NOT work well because it would a) be too far to pull the water right along the bench, and b) would increase the amount of "lift" distance. It might work, but I'm a bit sceptical.

#6b I think some containers (5L water bottles perhaps) that could easily be filled and have a small hole at the bottom so they drip-emptied over 12 hours, or less, would be fine. Could put as many of those on the bench as necessary, but they would take up some plant-space

#6c alternatively put some drip irrigation or leaky-hose along the middle of the bench, on a timer like any other totally automated irrigation, wetting the matting. No need to have to put individual dippers in each pot, so would work well when the population / layout / repotting of the greenhouse changed

#7 I've been very well pleased with the moisture content of the pots. All pots seem to have had a decent "wetness" at all times. (Obviously not if the matting were to dry out ... but in terms of the benefit for the time taken to just chuck a can of water in the reservoir I think it has been excellent).

Only possible downside is that I haven't been able to let anything dry out before next watering it. This would suit some plants better, and might even suit my Box cuttings etc better than being constantly moist.

#8 I'm not sure that Flood and Drain would have been better (well it would if 100% automated). Filling the trays and then needing to drain them might take longer if having to wait 5-10 minutes and then manually pull the drain-plug.

So my conclusion, and maybe next year's experiment, is "flood irrigation with sand substrate"

My thinking is that capillary watering would be achieved with sand in place of capillary matting. Roots that came out of the bottom of the pots, into the sand, would not be broken when the pot was lifted (assuming they were not too big to come back through the drainage holes when repotting, but if they are then they would be WAY overdue for potting on anyway!)

If I could combine trays containing some sand with flood & drain then I would have the benefit of "chuck 20L of water in the reservoir", plus the ability to run the plants drier before next watering them.

This would also work outside perhaps. I have an area alongside the greenhouse lined with pond-liner and then 1" of sand on which I stand plants. When it rains hard they sit in water until it has been drunk / evaporated (not really a problem in even a wet Summer, but not good in Winter). But watering is a doddle because I don't have to try to water each pot, just generally get X-Litres of water onto the plants, pots, sand as it will be shared by reservoir/capillary action. Again, leaky hose and timer would do the trick.

Liner & Sand also has the benefit that the base does not have to be perfectly flat - the sand can be made approximately level, but a pot sitting on it will make good contact with the sand - whereas a pot sitting on a 1" overlap joint between two pieces of capillary matting is then sat at an angle and the quality of the contact is dubious; also the flatness of the bench, and its joints, comes into play.

My thinking is to just not leave anything in the sand-reservoir over winter, or to come up with some way to "open" a drain-cock at the lowest end in Winter.

 

The matting tends to pull water until it hits its saturation level, mine levels out at about 7L sq/m and a lot of that is lost to evaporation rather than the plants. Its self perpetuating to a degree as the increased evaporation only serves to pull more water from the reservoir.
I`d be a bit wary of wet sand as it could turn a bit anaerobic. I`d do a small scale test to see what impact the sand will have on the PH of the feed water as it passes through. If it gets too alkaline its likely to create problems with nutrient availability in the pots, especially iron.

 

My matting is covered with micropore plastic, and then the pots on it are nose-to-tail (although they are round pots, not square), so my expectation was that the evaporation would be "modest" as none of the matting can really see the sun. However, if I am getting more evaporation than I expected it will be contributing to more humid conditions around the plant itself, which sounds like a good thing

My annoyance is really just that my downpipe around the bench isn't a big enough reservoir! My plan had been to "just chuck a bucket of water in the reservoir" once a day ... best laid plans and all that! I probably just need a bigger tank, a bit higher up, that can slowly replenish the downpipe distribution reservoir

I'm keen to use rainwater whenever possible, and thus a bit reluctant to hook it up to a timer on the mains. (I have a mains-tap by the greenhouse, but no electricity for a pump from the water butt - although I suppose a poxy solar pump might do enough - and it would pump more on sunny days, which would make sense ...)

Good points about the sand. Perhaps I should stick with that on just the outdoor growing-on areas.

Or use gravel instead perhaps?

 

Gravel works quite well for traditional flood and drain, ph can be an issue with that too but its usually ok if you give it a good flush with water before using it. The plants will enjoy the extra humidity but i guess it all comes down to how much water you get through in a week An elevated 220L waterbutt would make a good reservoir, fit a miniature float valve in the capillary mat downpipe and you`d be all set.
I use about 30L a day, which isnt too bad for 50+ tomato plants

 

Two season on, and if (when?!!) I do it again, I would choose Flood and Drain. Many plants are two wet on capillary matting, although the ability of the matting to hold water means that nothing goes dry easily.

I have lots of slugs and snails this year (everywhere, as does everyone else), but I wonder if this is made worse by capillary matting - nice damp atmosphere for them, but it may be the numerous hiding placed between the cheek-by-jowl way I have covered the staging in pots which is actually the culprit. I lightly sprinkle slug pellets on the matting, before putting the pots down, and then one-pellet-per-pot, but still find lots of slugs and snails ...

One issue to consider is what happens to plants that are overdue for potting-on or moving-out (I'm sure I am the only person in the world who does not pot-on / move-out plants immedaitely that they need it!). Capillary Matting, with micropore sheet on top, does a good job of allowing roots to grow out of bottom of pot, and live on top of sheet, or enter into it but restrict root growth, so the plants are generally fine and not too stressed when potted-on / moved out / planted out. I also have standing areas outside, on sand, and obviously plants can grow major root systems into that - they lift easily, getting the roots out of the pot can be a challenge!, but if careful the whole root system can be retained. I figure that gravel (rather than "nothing") in the bottom of Flood and Drain trays will do same / similar. It will dry out, in time, but it will provide a moisture and air combination until then.

So time to try a Flood and Drain system I think.