ON WALL GARDENS 37 
trees. Inthe latter case, and alsoin the case of the double- 
faced walls already described, one of two methods will 
be necessary to ensure adequate moistening of the whole 
root run of the plants. The one method is to lay a hose 
pipe on the soil behind the stones, and allow water to 
run gently, not forcibly, for several hours, then moving 
as far as necessary, and allowing another portion to be 
thoroughly soaked, and so on, until the whole area of the 
wall garden is treated. The other method is to sink, at 
regular intervals along the top of the wall, bottomless 
barrels or sewer pipes, and fill these to the brim with water, 
re-filling as it sinks away. Always remember, that if a 
wall garden is to be watered at all, it must be done on a 
sufficiently liberal scale to thoroughly soak the ground 
to a good depth. This is only necessary when drought 
is so severe and prolonged that plants appear distressed, 
but one thorough watering will suffice for a long period, 
and is worth more than any number of mere surface 
waterings. Although it is advised that the top soil of a 
wall garden should be flat, and open to receive the benefit 
of all rains, it is by no means necessary to leave it bare. 
Many plants will thrive in such a position. Centranthus 
ruber, Antirrhinums, Verbascums, Helianthemums and 
Cistus, Dryas octopetala, and many kinds of Dianthus, 
will provide sheets of colour and effective foliage, and 
whilst the rain will drip from their foliage to the earth, 
their shade will help to check evaporation during hot 
weather. 
The great advantage of even a short, low wall, is that 
in a narrow space that as a bed would take but a thin, 
