The hardest part of creating a bathtub container garden is moving your heavy new planter to where you want it to be. Plan carefully, because you'll probably not want to move it again after it's planted. Select a site where the garden you want to grow can thrive, then use your imagination. Whether you want a tub of bright blooms, trailing vines or salad vegetables, a bathtub container garden may be just the planter you need.
Prepare the bathtub for its new use by making sure it is clean and will drain water. Wash it with a 10 percent bleach solution, rinse it well, and let it dry. Drill at least six to eight holes in the bottom of the tub, using a 1/4-inch drill bit. Larger holes will allow too much soil to escape. If the tub sits up off the ground, the holes can go in the bottom of the tub; otherwise, drill them on the tub's sides, about 1/2 inch from the bottom.
Fill the bathtub with a soil mix for container gardening. Use a commercially produced mix, or create your own, using equal parts compost, pasteurized soil and perlite or vermiculite. Add 1 cup of 5-10-5 or 10-10-10 fertilizer for every eight gallons of soil mix. Don't use regular garden soil or transfer soil from the ground -- it will be too heavy and may contain diseases that would proliferate in a container garden. Fill the tub so that 2 inches of space remain at the top, giving you room for a layer of mulch.
Choose plants that thrive in your climate and in the amount of sun your bathtub receives. Select plants of various heights, as well as some that spill over the side of the bathtub. Plant them closer together than you normally would, to encourage a bountiful look.
Water the bathtub container garden at least daily during the growing season -- more when the temperatures climb -- especially if the tub is in full sun. Soil in container gardens dries out faster than an in-ground garden does. An inch of mulch around the plants can help maintain moisture and soil temperature.
Fertilize with a water-soluble fertilizer throughout the growing season. Add 2 tablespoons of a 10-20-10 fertilizer to 1 gallon of water and use this to water your plants every two to three weeks. You do not need to fertilize within the first eight to 10 weeks of planting if you added fertilizer to the soil at planting time.