A soil block for pot plant cultivation having a water-retentive layer, a hydrophobic layer above it, and a soil layer above that is provided. The water-retentive layer may consist of a sand layer, a water layer or a sand layer retaining water. The hydrophobic layer may consist of hydrophobic particles which are sand and/or dirt particles treated with a water-repellent agent, a water-repellent membrane including nonwoven fabric, woven fabric or knitted fabric treated with a water-repellent agent, or such. According to the method of cultivating pot plants, the pot plants are planted in the soil layer, which is the upper layer in the soil block for pot plant cultivation, and water is supplied to maintain the water content in the water-retentive layer at a constant level.