Watering your plants and seedlings from below in the greenhouse

An other Eli experiment in the greenhouse, so you don’t have to.

Consistent, hassle-free watering is the absolute holy grail of gardeners, be it a daily thing or if you were planning on going off for a wee holiday (one-day folks, lockdown won’t last forever). To an extent, I have this covered with my quadgrow units that let me water my tomatoes, peppers and herbs consistently but what about other plants, what about those tender seedlings? Seedlings perhaps are where watering is at it’s most important.

One of the things about watering the normal way, which for most of us is with the garden hose or watering can, is that to water our plants this way, we drop the water from above, hitting the leaves, splashing in the soil and causing a crust to form on the soil. This is undesirable for a few reasons, firstly the splashing in the soil is one way to spread soil born infections and fungi around your plants and seedlings. Not ideal. Also, and not a lot of folk seem to know about this, but watering from above, can cause a hard skin or crust to form on the soil which may not be an issue for most plants, but for tiny little seedlings, you can imagine how much harder this makes life for them.

So, it may seem obvious but if you shouldn’t water from above, then…….. yup, water from below. However, this is easier said than done. The standard practice and one which you will see commonly on gardening shows on tv is to stand the pots and seed trays in a tray of water for long enough to let the moisture soak up from the bottom. This works brilliantly, hence why it is standard practice but it takes time if you have a lot of pots and trays to water, not to mention you need space to do this. So I have been experimenting over the past few weeks with creating a capillary bed for my greenhouse, to make life a little bit easier. Not only does it water from below, but it provides a reliable and consistent level of water, not too much and importantly, not too little. And because I add a bit of water to a reservoir and leave it – bonus, it also covers my backside for those days when I forget… don’t judge, we’ve all done it.

The name capillary bed makes this sound so much grander than it actually is. Basically I have some capillary matting, which is a thick cloth which absorbs water easily, and I have it laid out across a flat surface. The pots and trays can then sit on this securely.

I also have a gap at each end of the bed where I can pour some water, then the matting soaks that water up and it spreads across the mat, creating a damp “bed” which the pots sit on. It works using the same principle as my quadgrow systems, just on a much bigger scale.

Now the important thing here is that the bed (where the pots sit ) is above the water, plants in most cases, do not like to sit in water – which is often referred to as not liking having wet feet. So you create a surface above or to the side of the water reservoir where the plants go, making sure it’s a flat even surface, then the matting can pull the water appropriately without the need to create a swamp.

I have to be honest, I was VERY sceptical about this. I have been testing it out in various formats for the past few weeks and I wasn’t 100% sure it was working. Mostly because my research method was deeply flawed. I had too many variables to be able to judge things properly. So I went back to the drawing board when creating this bed and I added a control, so I could say for sure if it was working or not.

Basically it was just a small pot with soil in it, but no plant. This meant I could monitor the moisture in the soil to see if it changed. In all honesty, I was completely expecting to tell you this didn’t work, and in the youtube video below you can see the moment I have to quickly compose myself when I realise the video wasn’t going to go the way I expected.

I turned the pot out to find damp soil – hurrah! It works, and I have a control and a method to prove it.

So if you fancy trying this out for your greenhouse, or even better, if you were planning on going away and wanted to make sure your houseplants survive, because yes you can do this using your kitchen sink and draining board. Then here is the skinny….

Here is what you need to do

1. Over a flat surface, lay out a length of capillary mat, long enough for your plants to sit on and with a bit left over to sit in the water reservoir. It needs to be flat so that your pots and trays can sit on there and be level.
2. Ensure the area of the mat where your pots sit is not actually in the water itself, except for the overhang.
3. Add water to the reservoir and give the mat itself a bit of a soak. It needs to be wet to get things started.
4. Place the pots on the mat and give them a light water, again to start the process.
5. Now just keep an eye on things, and ensure the mat doesn’t ever dry out.

Things to be aware of

1. I’ve already mentioned that you don’t want the plant pots to be sitting in water, but also, you don’t want to just fill your reservoir and leave it either. That stagnant and potentially “open to the light” water may then be affected by algae and other yucky things. So add just enough water to ensure your matting gets properly wet, and then drain off any excess.
2. Make sure your pots have drainage holes in the bottom.
3. Make sure your bed is level, if the holes in the bottom of the pot are not in contact with the matting, they can’t absorb the water.

So there we go, simple, efficient and regular watering for your plants. Another Eli experiment in the greenhouse done.