This is another of those garden tasks which you'd think doesn't need any explanation, but I keep coming across gro-bags with plants jutting out of them, with only half the rootball inside the gro-bag: or gro-bags which are rock hard and bone dry, with the owner anxiously telling me that they water them every day, but the plants are still dying.
So what is a gro-bag? It's an undersized bag of compost, commercially produced, made to be long and flat. They are laid direct on the ground or up on frames, they are more or less a standard size, and they are intended to be used for the growing of crops - outside or, more often, in greenhouses - where there is no soil to be planted into.
The bags are self-contained: you cut a small hole or slit in the top, insert your plants - usually three per gro-bag - water them, enjoy them for the summer, then discard the whole thing at the end of the season.
Not exactly “eco”, but oh! so convenient!
They work because they hold all the compost neatly inside(no spillage), they hold water well (few drainage holes), the compost has enough nutrition in it to get plants started, and because they are only intended to last for one season, it doesn't matter than they will be pretty much exhausted by the end of the season.
So where do people go wrong? They are manufactured and delivered to the garden centre in enormous numbers, stacked on pallets, which leaves them flat as pancakes. Very easy to move, but not so easy to plant into.
So when you get yours home, take them to their final location, then stand them on their side and gently squash them with your fist. Turn them gently over, and repeat.
Why gently? They have one long seam along the bottom, and if you treat them too roughly, this seam will split: a cunning ploy by the manufacturer to get us to buy more of them, no doubt. If this does happen, though, just turn them upside down and use them with the split edge on top. There is nothing to say that you have to use them with the pretty printed side upwards.
After squashing, take hold of each corner in turn, and shake it a little, until the compost within comes loose from the corner. Then flop them down flat again, and pat them back into shape.
This de-compresses all the compost inside, including the corners (which is often wasted), and makes it easier to insert your plants, and a great deal easier to get the water to stay in the compost. It also makes them deeper, which means that when you make a planting hole, you are less likely to hit the bottom of the bag and accidentally rip it.
Having fluffed them up, you can prick a couple of small holes in the underside, then cut holes in the top, and plant them up with ease: and when you water them, the compost is already nice and “open” and able to soak up all the water.