Contributed by Oldtimer1:
WHAT IS CAPILLARY MATTING?
Capillary matting is an absorbant fabric upon which pots are placed. Typically, plants are top fed with the runoff being absorbed by the matting. The matting holds the moisture until it is taken up by the plants through their bottom roots through capillary action. Many growers are now using this system and generally the findings are it helps even the plant growth giving a better overall yield. This improvement is due to the way some plants may use more water than others and completely dry out their rootball. Capillary matting is best used in a SOG or SCroG setup, where all of the plant tops are the same distance from the lamp.
SEVERAL CHOICES
In Europe we have choice of several different makes of cap matting, it also comes in different thicknesses and water retention capacity depending on what its used for. A very thin type for instance is used as a spreader mat covering the base of NFT tables giving an even all over coverage of nutrients. To the very thick water retentive type used by us which holds 1.4 us gallons per sq meter without any run off on a flat surface. They are made of a rot proof material and last several grows without breaking down. Ordinary felt is usually made from wool waste and will break down and rot faster. However, it is universally locally available, so it will do in a pinch.
HOW IT WORKS
Once you have worked out how much water your system uses [see below] If you water the amount your system takes, the plants in a normally dry condition will evenly re-wet their compost to saturation level any excess will drain out to the cap matting, where it is absorbed. However, any really dry rootballs will have shrunk back from the pot walls and most of the water applied will go around the edge of the root ball to the matting leaving the core still bone dry. Over the next 3 hours the capillary action started by watering will gradually saturate the the root ball core to whatever level your compost mix can hold. Once all the root balls have equalised the cap matting should be completely saturated but not flooded and under water. Plants that use more water will draw it from the cap matting as they need it light users will not and once the plants have been growing under this system for a week or two the plants seem to equalise and are much more even than plants in separate plant trays.
HOW MUCH WATER?
It is best to wait until your plants are in their final pots and rooted through. You can do the following method and, providing you use the same pot size and soil mix each time you grow, the data may be reused grow after grow. You will need a graduated watering container (or some other method for determining how much water is used).
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When watering using cap matting for the first time go lightly and measure carefully.
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Water slowly through each pots until you just get some run through.
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Leave it for an hour or so then go back and water the cap matting until it is just saturated to the surface, leave again for an hour and if the water has been sucked up add some more, keep doing this until no more water is taken up.
If you measure how much water it took to do this starting with dryish compost rootballs you will now know how many litres/gallons the system holds and how much a full watering takes. I know this seems to be a bit of a faff but you only have to do it once. Every time you need to water this is the amount of water you will use, it will stay the same through out your grow. All that will change is the time between watering. If you are in a hurry and your plants are dry you can just empty that amount of water straight onto the cap matting and your plants will draw it up. I dont recommend you do this all the time especially when you are feeding, we find we get better results feeding through the top of the pots but do use the same amount of fertilised water as you would when watering normally.