The cold winter has helped dandelions prosper and they are now out-growing other plants. Extra use of fertilisers is helping the weed bloom, while EU rules cutting pesticide use mean council gardeners are not allowed to use weedkillers on the yellow flowers.
Westland Horticulture head of horticulture Dr Mark Fletcher said: "Part of the problem has been that the councils and people responsible for road verges and central reservations seem to have cut back or stopped the use of selective herbicides over the last few years and hence you have more dandelions than normal.
"Added to this, the mowing regimes have helped the spread. It seems that mowing in these areas doesn't happen now until mid to late May and by then the dandelion has passed flower and gone to seed, hence increased numbers every year as the mowers help scatter the seed."
Sheffield University senior research fellow Dr Ken Thompson pointed out that dandelions were drought-tolerant on account of the deep tap root, while the cold weather might have slowed down grass growth, making it look as though there were more than usual.
Thompson added that because dandelions liked fertile soils they will gradually increase as we use more fertiliser and nitrogen. He suggested recent scares about aminopyralid in manure may mean farmers are using less weedkiller.
Reading University weed biologist Dr Bob Froud-Williams said: "The long cold winter has delayed growth of grass. Reduced sward height may have enabled the dandelions to be more visible.
"Secondly, roadside verges have not in general been cut as yet and so defoliation and inflorescence removal hasn't occurred." He added that dandelions may have survived the cold because they store carbohydrate as the fructan inulin, which acts as an "antifreeze".
He recommended one of the auxin type herbicides such as mecoprop-p, usually applied in combination with dicamba + MCPA or alternatively dicamba + dichloprop + MCPA. In agricultural grassland, clopyralid or triclopyr may be used.
Plant life species recovery officer Dominic Price called for the public to take part in a wild flower count to gauge how the dandelion explosion is affecting other wild plants.