I am using an automatic watering system for the greenhouse staging and for the seedling table in the conservatory. It is all down to that genius Geoff Hamilton who showed a similar system on GW about a decade ago.
I covered a large table (folding wallpaper table in my case) with a double
layer of plastic sheet, raised the edges all round with bamboo canes wedged
underneath the plastic to stop water dripping off. Then covered the plastic
with capillary matting cut to be a little smaller than plastic, again to
prevent drips. A large gravel tray (bigger and deeper than a seed tray, no
holes in the bottom) was put on a stand by one of the narrow ends of the table, with the top of gravel tray coming up up to just below the top of the table. The
drop from the table to the bottom of the gravel tray should be 2-4 inches - no more.
I cut a'tongue' out of capillary matting 2 inches wide to fit into the gravel
tray - the tongue is sized to fit over the edge of the plastic and fully down
into the tray. Just filling the tray with water lasts for several days. To start the process, the capillary matting must be dampened. By the way, it is not necessary that the tongue and the rest of the matting are constructed from the same piece. The tongue can be cut and the end not in the water reservoir placed underneath the rest of the matting with a good overlap, as long as they are in contact with each other.
But if auto-watering is needed for longer, I take a camping water
bottle (5 gallons - rectangular plastic) and fill it. Then I put 2x1ft long
(1 inch high 1/2 inch wide) pieces of wood into the tray and invert the bottle
over these - so that the neck of the bottle is held just clear off the
bottom of the tray by the wood and the 'shoulders' of the bottle rest on
the wood. Placing the bottle requires strength and about 3 hands - the bottle is
heavy to start with and needs to be inverted with one palm closing the neck
to prevent all the water gushing out! It may be easier to place the bottle
with its stopper fully closed, ask someone else to tip the bottle slightly
whilst removing the stopper swiftly before the gushing water overfills the
gravel tray. When I am on my own, I can only half fill the bottle and stop the neck
with one hand whilst placing it in the tray upside down.
When everything is in place, the capillary matting transports water from the
tray and waters the plants on the table automatically. At the rate the
plants demand it. This really helps with damping off as well. There is no
dripping from the table onto the floor. When the water
level in the tray drops to below the neck of the bottle, water 'glugs' out and
the tray refills automatically.
For the greenhouse staging version I used two inverted shelves from an old metal
shelving unit. These have raised corners, so no bamboos needed like on the
table. Then plastic sheet, followed by matting as above. These shelves
are located side by side placed on top of the staging with the water
reservoir in the middle between them. This reservoir has a matting tongue
from each side going into it. The only consideration is that the reservoir
is located slightly lower than the shelves, so that the matting tongues go
down and bring the water up.
Hope all this makes sense, sorry its a bit long.
