What to do
As the weather warms up, greenhouses will need more frequent damping down. High humidity helps flagging plants, but also discourages red spider, which is a difficult pest to eradicate. Artificial shading, with blinds or a glass wash, may also be necessary on greenhouses in full sun.
Cordon fruit trees, as well as espaliers and fans, have a habit of throwing out shoots where you don't want them. Pinch out any growths that are pointing towards the wall, or that are growing too close together.
Check for greenfly on roses and other known targets. Ladybirds are now active, so if you must spray, use an insecticide designed for aphids.
Sow Shirley poppies, love in a mist, eschscholzia, clarkia and cornflower where there are gaps to fill. They will be late into flower, but better than bare soil. Rake the soil first to make a fine tilth and firm the ground with the back of a rake before sowing seed. Cover very lightly with earth.
What to see
For the past 15 years the London Parks & Gardens Trust has been building up an inventory of the capital's green spaces: parks, squares, public gardens, cemeteries and churchyards. This week, the LPGT's extraordinary archive (it covers more than 2,500 places) goes online, illustrated with plans and paintings provided by 33 London boroughs. Go to londongardensonline.org.uk