IN GARDENS in London, hard surfaces and new buildings are replacing vegetation at the rate of two-and-a-half times the area of Hyde Park each year. This is the finding of Greenspace Information for Greater London (GIGL), 2013, the capital's local environmental-records centre.

GIGL states that: "Hypothetically, if the loss of green space observed during the period of study were to carry on, we would lose all of our garden green space by the year 2068." In reality, of course, such a straightforward linear decline will not occur, but the trend is still worrying.

Planning legislation can help to restrict extensions (one of the main factors in loss of green space) and paving over front gardens. Planning permission is needed to pave more than five square metres of a front garden. In a back garden, however, we are all at liberty to replace flowerbeds and lawn with patios and decking, should we wish to.

Paved areas are desirable as routes through a planted space, providing safe, dry access at all times. I cannot deny their appeal, alongside abundant planting. With a bit of thought, their impact on vegetation can be reduced.

Gaps are key here. Remove some slabs randomly, or, better still, downsize to stepping-stones. Chip out the mortar between blocks, and replace with loam-based compost. The aim is to create new planting opportunities. No plant will withstand constant trampling, but if footfall can be kept mainly to the peripheral stems, low-growing thymes are a good choice for forming carpets of scented evergreen foliage.

Varieties of wild thyme, Thymus serpyllum, make a dense mat, and bees love their flowers. Lemon thyme, Thymus citriodorus, has a strong lemony fragrance, and is available as silver or gold variegated forms, both of which produce tiny spires of pink flowers in summer. Woolly thyme, Thymus pseudolanuginosus, rarely flowers, but has lovely fuzzy grey foliage, and is a vigorous spreader.

Paved areas in shade can be enhanced with Corsican mint, Mentha requienii, that when brushed gives off an invigorating minty aroma, or Arenaria balearica, which is covered with white flowers from March to July. Other choices are lesser periwinkle Vinca minor, or self-seeding heartsease, Viola tricolor.

For areas that are not walked on very often, such as the corner of a patio, creeping speedwell, Veronica prostrata, with its show of true blue flowers in early summer, and bugle, Ajuga reptans, would both be popular with bees. The rock phloxes, such as Phlox douglasii and Phlox subulata, form tight evergreen mats of narrow leaves smothered in pastel-hued flowers in spring and early summer.

The GIGL study focused on London, but its findings are bound to relate to all our urban areas. Individual gardens may be small, but their sum is significant, and we can all do our bit to ensure green wins over grey to support garden biodiversity.