Plastic Grow Bags
For that "in the ground" feeling
Plastic grow bags range from small hanging versions with pre-punched drainage holes, suitable for hanging on walls, drainpipes or any place you've got a hankering to see a burst of blooms. You just plant spreading plants in the holes provided - and wait until it fills out into a bag of blooms. Watering these can be challenging - but putting a piece of perforated pipe in the center to conduct water to all the plants proves very helpful.
Or you can try the new garbage bag gardens - large specially treated plastic bags that hold up to 11 gallons of soil. Just lay them on the deck and add fertilizer, plants, and water. If you plant trailing and spreading plants they will cover the bags so that no one will ever know your garden is growing on a plastic bag. The big ones have enough soil holding capacity that you can plant veggies, too.
The economy version of this is to buy a bag of potting soil, punch holes in it and plant. Make them big holes or watering could be challenging. Needless to say, these are one-season gardens.