PLANTS FOR DIFFICULT SITUATIONS - UNDER PINE TREES

Progress report: Alec Cobb,   3/02/2012

THE SITE

The experimental plot chosen, 3m x 1m, is situated under a mature Pinus halepensis estimated to be around 75 years old and 12m in height.  The plot is around 3m from the base of the tree and a similar distance in from the drip line.  The tree is the last in a short row of 3 mature trees with a group of established Thuja orientalis planted close by on the eastern side.  The test plot has a southerly aspect and receives some sun in the late autumn/winter/early spring.  The amount of sunlight falling on it is, however, moderated by a pergola with climbers to the south and also by a low wall with balustrades enclosing a deck area to the west.

The soil is a stony, heavy clay type generally alkaline in pH.

PLOT PREPARATION: September 2011.

The “thatch” of fresh and partially decayed pine needles was raked aside and after a thorough watering was forked over to a depth of 20/25cms, limited by the network of roots from the tree.

The soil was “improved” by the addition of around 60g/m2 of a general-purpose inorganic fertiliser. 

For comparison purposes, two simple rain gauges were installed, one in the centre of the plot and the second some 10m away in the open garden.

PLANTS CHOSEN

The plants listed below were chosen based on members’ recommendations and those selected from “The Dry Gardening Handbook” by Olivier Filippi. Plants already growing close by and tall growing species were discounted.

Acanthus mollis

Cymbalaria muralis

Geranium sanguineum

Helleborus argutiflorus

Helleborus niger

Teucrium chamaedrys

Teucrium x lucidrys

PLANTING

The opportunity to plant out was taken following the first significant rainfall in my area over the period 25^th to the 29^th of October. During this time a total of 66.5mm of rain fell in the open garden area of which a total of 37.5mm fell on the experimental plot.

PROBLEMS

1. Holes appearing in the leaves of the Acanthus mollis appeared to be the work of slugs.  An attempt to dissuade them by spreading a layer of fine sharp gravel did not appear to be successful so a propriety slug pellet bat was resorted to.

2. Water. Over the period Oct/Nov 2011 a total of 224.5mm of rain fell of which only 112.5mm penetrated the tree cover. Over the 2 months to the end of January 2012 no rain has fallen onto the test plot.  This together with a spell of warm weather followed by cold drying winds has necessitated watering on 2 occasions to revive flagging plants.

Depending upon the duration and intensity of the rainfall it has been observed that some 15 to 25 mm of rain are required to break through the needle cover.

OBSERVATIONS

Slugs apart, the Geranium sanguineum plants appear to be struggling the most.