Pot plants are different from garden plants when it comes to the question of watering. It often does not hurt a garden border to be allowed to become almost dry, as the plant toots are able to draw moisture from a considerable depth, though the amount of water in the top few inches of soil is almost negligible.
If a pot plant is allowed to dry out at any time, not only do the roots become dry, but the ball of soil in the pot forms into a hard lump ami cracks away from the pot sides, with the result that subsequent waterings do not penetrate but merely drain away quickly down the sides of the pot. It is essential, therefore, that the water supply should be fairly constant where pot plants are concerned. At the same time it is a very unwise practice to allow the pots to stand in saucers filled with water, as this prevents air from reaching the roots and is often the cause of fatalities.
To ascertain whether a plant in a pot is in need of water, tap the pot smartly on the side with the knuckles. If the sound is dull, no water is required; but if it gives a hollow ring, water should be given at once.
Further particulars concerning cultivation of annuals in the greenhouse will be found in the section dealing with greenhouses and cold frames.