Adding a handful or two of shredded cardboard to plant pots helps to stop them drying out in between watering. The cardboard fragments absorb the water, so the liquid doesn't pass through the soil too quickly for plant roots to make use of.
I also add shredded cardboard to the flower-beds and veg-beds in the garden, to retain moisture and to stop nutrients being washed too deeply into the soil. Make sure you cover the shredded carboard with regular soil / peat-free compost and immediately water the area well, so you don't end up with bits of dry cardboard blowing around your garden in the wind!
Plus shredded cardboard gets added to the tumbling composter each week, to ensure the quantity of green matter (fresh fruit and veg peelings) matches the quantity of brown matter (such as shredded carboard).
Coconut coir is often-suggested when trying to boost soil moisture retention - but coconut coir comes packaged in plastic and (for gardeners in the UK) it will have travelled a long way from much sunnier shores, giving it a hefty carbon footprint. Cardboard on the other hand is in plentiful supply in our house (as we have done much more online shopping than usual) and most was just destined for the recycling bin. The thick cardboard (which our shredder can't cope with) we save to use as biodegradable weed-control matting.
Ripping up enough cardboard is time-consuming, so nowadays I use a fairly heavy-duty paper shredder (which is designed to handle 12 sheets of paper at once). I got this Bonsai shredder for under £50 from Amazon when it was on offer. It can manage Amazon-thickness cardboard boxes, but I wouldn't try and shred any thicker boxes and we ALWAYS follow the safety guidance which is to limit shredding time to 5 minutes followed by a 40 minute switched-off rest time, to avoid overheating the shredder (not a good idea when what it produces is so flammable!)
We only use plain brown, virtually ink-free cardboard for shredding (so not heavily printed cereal boxes for example) to avoid contaminating the soil with unwanted chemicals. Also (obviously) remove all plastic tape, sticky labels and hidden plastic 'easy open' pull strips before shredding.
If you don't have a shredder then start saving egg boxes (and ask family and friends to save them too) as egg boxes are easy to tear up into teeny-tiny pieces by hand.
When the weather is hot and dry, you will really notice a difference if you add an handful of shredded cardboard / ripped up egg boxes to your pots - your potted plants will be much happier. The tomatoes we are growing on a windowsill have gone from permanently thirsty to flourishing, thanks to the addition of shredded cardboard. Try it!
