Better than other products for doing this because the tapered cone fits so many different bottle types. Much better than the wine bottle versions because so much more easy to refill - just cut the bottom off plastic bottle and fill with your regular watering can. (No reason to go back and forth from your sink so many times.) Better than the spikes because these disperse the water evenly, not just through a hole in the bottom.
Just fit this adapter into almost any standar plastic bottle, fill the bottle with water, and push into the soil near a plant. The porous cone will slowly start to distribute water throughout the day. The regular size does about 200 milileters (.43 pint) during a 24-hour period. The XL, larger size does about 300 milileters (.63 pint).