Geodesic Dome Greenhouse - milk jugs right next to the plants in the spring to pick up heat during the day and a garden hose from the water pump around the outside of the greenhouse, right next to the plants. The hose is much warmer than the air at night.
Flower Pot Drain Hole Cover: Just lay a coffee filter in the bottom of the pot covering the hole before filling the pot. The soil will stay in the pot and the water will still drain out because that is what coffee filters are designed to do; let water through. They last for a long time, too; by the time they fall apart, the potting soil is well packed and the plant has roots that hold the soil together.