Best composted rather than just dug into the soil. Make sure the 'bag' is paper and not something synthetic which won't rot down, if it is snip the bag open and only add the tea leaves to the bin.

Tea bags tend to contain finely broken pieces of tea leaf, so they're actually more suitable for direct application to the soil and they break down more quickly than loose leaf tea.

Sprinkle the contents of the tea bags around the base of your plants and gently mix them into the soil. It is particularly good for acid loving plants including tomatoes and roses and they are especially liked by Hydrangeas.

Tea leaves contain N-P-K fertiliser as well as some trace minerals too. Spent coffee grounds is another thing that can be used in the same way.

As MG said, a lot of manufacturers have now switched from paper bags to nylon bags which aren't biodegradable.

My granddad's rhubarb was fed every day when he tipped the old tea out onto it from the pot. The pot itself was stained black. Always remember the lovely tea he made. The rhubarb was HUGE!

I also rip open the tea bags and put the tea leaves in the compost bin and the bag in the rubbish bin.