A self-watering tomato planter is less likely to dry out than other planters. These containers have a reservoir in the bottom that holds water, slowly leaching it into the soil to keep it evenly moist at all times. Even if you forget to water the planter for several days, there is still water in the reservoir for the roots to absorb. Self-watering planters are simple to make: a plastic 5-gallon bucket is just the right size for a single tomato plant, especially if you grow a dwarf or patio variety.
Cut the rim off the lid to a 5-gallon bucket, using a sabre saw. Trim the edges of the lid until it can slide down inside the bucket.
Drill 15 holes in the lid, 1/4 inch in diameter. Space the holes at an equal distance from each other. Drill a single 1-inch-diameter hole in the lid 1 inch in from the edge.
Cut a 4-inch-diameter drain tile pipe into three sections, each 2 1/2 inches long. Set these on the bottom of the bucket.
Measure 2 1/2 inches up from the bottom of the bucket. Drill a 1/4-inch-diameter hole in the side of the bucket at this point, creating the overfill drain.
Slide the lid inside the bucket until it rests on top of the drain tile pipes. Insert a 3-foot-tall length of 1-inch-diameter PVC pipe into the 1-inch hole in the bucket lid.
Widen a 1/4-inch hole to a 3-inch diameter over one of the drain tile pipe supports in the bottom of the bucket. Pack soil into this drain tile pipe, which acts as a wick to bring water to the plant roots as the water level in the reservoir begins to drop.
Combine a slow-release, general-purpose fertiliser with a soilless potting medium. Use the amount of fertiliser recommended on the label.
Fill the bucket with the prepared potting medium. Plant your tomato seedling in the bucket at the same depth it was growing in its nursery pot.
Water the soil from the top to evenly moisten it throughout, then pour water into the PVC pipe until the excess begins to drain from the overfill hole. Replenish the water in the reservoir once a week.
Cover the surface of the soil with a sheet of plastic mulch to help keep the soil moist and prevent rapid evaporation in hot weather. During hot, dry weather, you may need to fill the water reservoir more often.