In article , Steve
Harris writes
I'm growing some radishes early under a cloche and note that the soil
around them is already looking a bit dry. I'm also planning to do
outdoor tomatoes later in the year and read that black plastic on the
ground makes the crop better.

But how do I make sure the plants get their share of the rainfall?

Black plastic cannot improve soil for vegetable growing purposes.
At best it might deter some surface weeds, but in the case of tomatoes,
that would be better done by hoeing or hand weeding. Outdoor tomatoes
only need watering in times of drought if they are in good friable soil.
--
Alan & Joan Gould - North Lincs.