Unlike plants grown in the open garden, container-grown plants rely on you to provide a regular supply of water and food to meet their needs. Rain often fails to reach plants growing in containers and the nutrients in the potting mix will eventually be depleted after planting.
Watering
You will need to water your container plants more frequently when they are in active growth, usually in the spring and summer. Check moisture levels daily from mid-spring to early autumn – if possible, do this twice a day in hot weather. The best way to do this is by sticking your finger in the container to a depth of about 10 cm (4 in) to feel how dry the potting mix is. You can also buy a special gauge to read the moisture level.
When to Water
In summer, water early in the morning and again, if necessary, in the cool of the evening. Don’t water containers during the hottest part of the day. In winter, water in late morning whenever you think the plants are in need of a drink. Water will seldom be necessary in winter for deciduous or other dormant plants, although conifers and other evergreens may benefit from a little winter water.
How Often to Water
Bedding plants in containers will require watering every day, especially in the summer. Succulents and drought-tolerant plants like herbs will need less water. Mature and well-established plants can also survive longer without water than newly planted specimens. You need to water even if it has rained, as the foliage of the plants creates an ‘umbrella’ that stops the rainwater reaching the potting mix.
How to Water
The best way to water is to move from container to container with a gently running garden hose aimed at the potting mix. You can also use a watering can with a fine rose attachment. Although more time-consuming, this is better for plants with delicate flowers and leaves. Water the containers thoroughly, filling them to the brim and allowing the water to drain out. Fill the containers for a second time to ensure the potting mix is thoroughly wet. If you don’t see water draining out of the container, check to see if the drainage holes are blocked. Aim for slow, steady watering to give the potting mix enough time to absorb the water.
If you find watering a real chore, then you can install automatic watering systems that will drip water into your containers at set times. This might be helpful if you are going on holiday. You can also get adjustable water reservoirs that turn ordinary containers into self-watering planters. However, you will still need to pay close attention to the watering requirements of your plants and respond accordingly.
It can be easy to give plants too little or too much water. Signs that your plants are being under-watered include dropping petals, dry, shrivelled and discoloured leaves, and limp stems. You might also notice a whitish bloom on the foliage. If the potting mix has dried out completely, try rehydrating it and reviving the plant (see opposite).
Over-watering is a common mistake. Aim to keep potting mix moist but not soggy as plants don’t like sitting in wet conditions. Avoid letting the potting mix dry out completely, then saturating it.
Signs that you are over-watering include water-soaked spots on the leaves that develop into raised swellings or growths. These can burst and look white and powdery or rust-coloured and scaly. Don’t be tempted to remove the affected leaves, as this can make things worse. Instead, check whether the potting mix is free-draining (the drainage hole may be blocked, for example) – if it is too wet, it’s a good idea to repot the plant using fresh potting mix.
Watering Cacti and Succulents
If you grow these plants, perhaps for the Succulent Trough, use the soak-and-dry-out method: allow the potting mix to almost dry out before watering the plants again.
REJUVENATING A CONTAINER-GROWN PLANT
Even the most experienced gardener will have discovered a plant wilting sadly in potting mix that has completely dried out. To revive the plant, try moving the container to a cool, shady area. Soak the plant carefully on a regular basis and gently spray the leaves, and cut back any shrivelled foliage. You can also try plunging the container in a large bucket of water for about 30 minutes until the potting mix is soaked and the leaves starting to plump up again, then remove the container and allow to drain. Wait a few weeks before throwing the plant away, as you might find that it starts to sprout again – and all is not lost.
Tip — In hot weather, group containers together in a shady spot to create a microclimate that will keep the air around the foliage humid and the plants cool. This will reduce the heat stress experienced by the plants.