This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
Allotments and gardens are cultivated tracts which, however, have waste places contiguous to them, and the weeds in the garden are eradicated and turned out, unless they are burnt as manure, and perpetuate themselves upon the outskirts. The garden is a particularly suitable spot for the growth of the less sturdy, succulent herbaceous annuals with more dominant and vigorous plants that form wide associations. Their occurrence or frequency even in such spots is largely sporadic, their societies being small and discontinuous, and as a rule they do not form wide or large or permanent associations.
The worst conditions that such plants have to contend with are periodical multi-annual eradication and the dominance of the cultivated plants. All the other conditions make for their perfection, and it is surprising that they have retained, so far as we know, their characters under such artificial conditions.
There are a large number of plants common to garden ground, such as Wormwood, Groundsel, Milk Thistle, Mullein, Red Dead Nettle, White Dead Nettle, Fat Hen. Other common types are Cut-leaved Dead Nettle, Grey Speedwell, Henbit Dead Nettle, the terrestrial form of Amphibious Knotgrass, Fool's Parsley, Orache, Creeping Thistle, Twitch, Annual Meadow Grass, etc.
Apart from the manure heaps that are found in farmyards, there are others in fields, etc, but both agree in the conditions which give rise to the appearance of the plants that are especially found in such places. To a slight extent a manure heap acts as a barrier to, or receiving-house for, the seeds of plants blown thither by the wind. But this does not account for the large number of alien plants that occur upon the manure heaps. Doubtless these are partly brought there in excreta; but others are derived from sweepings mixed with the manure, with garden seeds, etc. And some plants may also owe their occurrence to the fact that a manure heap is used as a refuse heap, and large numbers of plants may thus become established which may be found in the village or town of the district.
On manure heaps such lovely flowers as Glaucium phoeniceum, Raemeria hybrida occur; also Raphanus, Canary Grass, and the Little Nettle. Kitchen middens or waste heaps often found near houses or old ruins, where there is frequently a black soil, due to the accumulation of refuse in one spot, are characterized by plants that have in the past been used for herbal remedies or in medicine, as Hound's Tongue, Henbane, Belladonna, Black Nightshade, Thorn-apple, etc.
Various factors enter into the characteristic habits of waste-ground plants. The richness of the soil may, as upon manure heaps, etc., cause the plants to have a diffuse, much-branched habit. The height is in this case greater than usual. Such plants as Common Mallow and Fat Hen often attain a great size. The soil of a garden has the same effect. The openness of the soil is one cause of this.
The hedge plants have the pyramidal or inversely pyramidal habit, as Greater Celandine, Goutweed, Tansy, etc.
The rosette habit is a common one where many plants grow close together, and where light is not well diffused. Such plants as Shepherd's Purse, Musk Thistle, Chicory, Mullein, etc., have this habit. This also is an advantage where the soil is dry. Common Mouse-ear Chickweed has a grass habit, with the leaf margins recurved, and with a hairy stem.
Many plants have the trailing or prostrate habit, but these are not found in the habitats in which many plants grow closely associated as a rule. They occur on sandy wastes, as Stork's Bill, or on banks, as Creeping Toadflax, or on gateways, as Knotgrass. The succulent Dead Nettles have stems at first prostrate, which helps to strengthen the stem. Burdock, Milk Thistle, Belladonna, are bushy in habit.