No! Not watering your bottom! Bottom-watering of plants! Honestly, you lot (rolls eyes).
You often read this term, usually in relation to seeds, but how many of us know what it actually means, and why we do it?
”Normal” watering is where you pour the water on from above, whereas bottom-watering, as the name suggests, is where the water is supplied from below. There are several ways to do this - you can stand individual pots in saucers, and fill the saucer; you can slot root-trainers (those black plastic modules, designed to form long roots) into their own upturned water-filled lids; or you can make your own plastic-lined tray for plunging pots up to their waists in water. In all these cases, you should remove the pots from the saucer, lid, or plunging tray after each watering, allowing excess water to drain away.
Of course, the easiest method for bottom watering is to use capillary matting underneath the pots, as you only have to fill up the reservoir from time to time, so it is very time-efficient.
All of these methods deliver water to the bottom instead of the top - and why would we want to do that? Well, there are several reasons, for different types of plant.
Starting small: with seeds, sloshing water enthusiastically over the top can wash the seeds to the top of the compost, instead of being safely tucked underneath it, which can affect germination.
Moving on to seedlings, an overhead deluge can knock them to the ground, causing damage to the stems and leaves directly; and by pushing the tender new stems into contact with the damp compost, this action can cause rotting. At the very least, it gives the seedling a major set back, and often results in lax, warped seedlings instead of sturdy upright ones. Furthermore, very tiny seedlings, especially in greenhouses, won't enjoy having great drops of water on their delicate little leaves.
For both of these, bottom watering using capillary matting is the best option, as your plants are constantly just as moist as they need to be, and has the enormous benefit that you can go away and leave them for a couple of days at a time, with a clear conscience.
For established plants, watering from underneath ensures that the compost is wet right the way down to the bottom, encouraging the roots to grow right through the pot, and not to just hang about near the surface, waiting for the next light shower.
Bottom watering is also the best way to retrieve neglected plants in smaller plastic pots (ie plants we are growing on for sale, perhaps) if they have been allowed to dry out too much: once compost has dried out, it is notoriously difficult to re-wet, and I am sure we all recognise that moment when you pour water on top, and it all runs straight through the pot and out again, not pausing en route. When this occurs, the only way to save the plant is to plunge the pot into deep water, waist high or more: eventually, capillary action will pull the water up into the dry compost, and all will be well. You can help the process by ladling more water over the top from time to time, and if the plant is so dry that it bobs up like a rubber duck, well, firstly you have to hang your head in shame for looking after your plants so badly (I can say this with a straight face, as I have done it myself, more than once!) and secondly you just have to hold the pot underwater until the air spaces have filled, and until it stops bubbling. In really bad cases, you may have to weigh the pot down to hold it in place.
In addition, here are a couple of general reasons for bottom watering: for a start, it doesn’t wash away the mineral deposits which accumulate on the top of the soil, along with the liquid feeds and/or slow release pellets which you supply. It also reduces the formation of a surface pan, or “crust”, which often occurs with top watering, and it also prevents, for those of you who are lazy waterers and who don't bend over to get the can or hose close to your plants, that horrible funnel-like hole which forms - usually close to the stem - on plants which are given a deluge from a great height.
So there you are, everything you ever wanted to know about bottom-watering!