One of the major killers of plants, especially in pots and containers, is too much or too little water. Water plants frequently in warm weather especially if they are under cover, in a conservatory or greenhouse. But don't let them sit in saucers of water, with the obvious exceptions of aquatic or bog plants.
Plants growing close to or next to a wall, will typically be in a 'rain shadow' so the roots will get little or no water. Water them well, particularly in warm weather and apply a thick mulch to retain the moisture.
To make sure that you are watering pots and planters with sufficient amounts of water, scrape away the top inch of compost and check that it is moist.
Watering just the top layer of soil will encourage plants to grow a shallow root system, which isn't too much of a problem with bedding plants, but it is obviously more important that you give a good drenching to trees and shrubs.
Particularly in the summer, the best time to water plants is in the early evening or in early morning, so the sun doesn't scorch wet leaves. If it's really dry, it may be necessary to water morning and evening. In the autumn and winter, if it hasn't rained for a few days and the soil is dry, water in the morning, but only briefly, otherwise the plant roots will be wet and cold overnight, which can lead to rot.
If at any time you have a plant that is wilting or obviously dry, water immediately, plunging any that are in pots, into a bucket of water for 10-15 minutes.
Watering different soil types
Because of its structure, plants grown in sandy soil will need to be watered with less water but more often. Plants in heavy, clay soil will need less frequent watering, but more water in each instance.
It should be assumed that the compost in pots, containers and hanging baskets fall into the sandy soil category.
When watering seedlings use mains water rather than water from a waterbutt, as this can introduce infection.
The long spout of a watering can enables the watering at the base of the plant, getting water to the roots and leaving the surrounding soil drier, which can reduce the amount of moisture available for weeds.
You don't need a watering can for indoor plants, use a measuring jug, or a freshly filled kettle instead.