Abstract: A greenhouse, to be provided in a window opening, includes an enclosed housing having a first operable window pane provided on the outer side of the window opening to allow air into the enclosed housing, and a second operable window pane provided on the inner side of the window opening. The windowsill of the window opening is provided with an elongated groove to serve as a plant box to contain soil to grow plants. A watering device is mounted on the enclosed housing adjacent to the second operable window pane. The watering device includes a receptacle to contain liquid to water the plants, a watering pipe member communicated with the receptacle and extending into the plant box, and a valve to control liquid flow from the receptacle to the pipe member. A surrounding temperature control device is similarly mounted on the enclosed housing adjacent to the second operable window pane.