How to enhance summer containers for colourful plant displays: Gardening jobs for the weekend

2022-07-08 07:07:15 By : Ms. XU CHRISTINA

With summer containers planted up and growing well, some tweaking now can enhance results for the rest of the summer. Light levels decline slowly from now on, so growth will gradually slow, despite increasing temperatures.

Tender or “bedding” plants are popular for summer containers, including cosmos, dahlias, fuchsias, lobelia, marigolds, pelargoniums, petunia and zinnia. These become less widely available after June, so consider herbaceous perennials to plant vacant containers. Good ones, in medium sizes, available from summer flower shows and plant fairs include echinacea, penstemons, rudbeckia and salvias.

For autumn displays, consider nasturtiums grown from seed and potted autumn flowers – aster x frikartii and Hesperantha coccinea are rewarding choices. Small plants offered in plugs are less satisfactory, as summer will be running down by the time they reach a good size.

Container plants respond well to deadheading, with further flowers and growth, particularly if suitably fed and watered. Watering is the most important factor in summer success. Ideally water to wet the container but not enough to run out the bottom. In practice this is difficult, and using a saucer try to catch surplus water is useful, as the plants can often reabsorb the retained water.

Knowing how much water to give can be tricky and some trial and error is often needed. Once plants wilt or go grey, they have been damaged to some extent. Overwatered plants develop dead, rotted roots and die back.

Water pots until the first signs of water running out are detected. Then lift the container to get an idea of the weight of the container when moist. In future, avoid watering if the pot feels heavier than this. Then wait until the first signs of stress appear and lift the pot again. Never let it get to this lower weight in future. It becomes easier with practice.

All too often water butts run dry in rainless summers, but grey water collected from the kitchen or baths, showers and sinks is satisfactory for the summer period, and reduces the need for mains water. A carefully adjusted automatic watering system can be economical of water when a timer is incorporated to deliver just enough to keep plants alive in dull weather.

Set it up to water in the small hours, when demands on mains water are at their lowest. Then top up by hand-watering if the weather is hotter and drier, ideally using rain or waste water. Remember that summer rain is seldom sufficient to satisfactorily wet containers.

When it comes to feeding, there is enough plant nutrients in potting compost to last about six weeks, after which supplementary feeding is necessary for the best results. One way of feeding is to add controlled-release fertiliser granules at potting time.

These are pellets of fertiliser coated with a resin or wax that allows water to enter to dissolve the nutrients, which then diffuse out. As both nutrient diffusion and plant growth depend on temperature, this works well. It is important not to overdose, as in hot weather more nutrients are released than the plant can use, which can lead to damage.

Tablets of controlled-release fertiliser can be added now which will feed plants for the next three months. Organic gardeners can add a sprinkling of hoof and horn, bone meal or other organic fertiliser to the top of the pot and lightly mixed into the surface. Alternatively, use liquid fertilisers. These are more work – typically being given every week or fortnight, depending on how fast the plants are growing. General liquid fertilisers are ideal.

Seaweed fertiliser is a good choice and suitable for organic growers. Home-made fertilisers – made from comfrey or nettles, for example – are very weak, so should be used often. Vegetables in containers need particularly lavish feeding, with tomatoes being a special case, responding well to ample potassium, as found in tomato feeds. Houseplants taking a rest in the garden will grow much more than when indoors and will repay feeding for when they come back in later.

Some popular perennial container plants are grown for winter foliage and colour – camellia, primula and skimmia, for example. Keep these in a sheltered shady spot, such as against a north-facing wall, with water but no fertiliser until autumn.If you are going on holiday and do not have automatic watering systems, a helpful neighbour might step in – but arguably a properly remunerated young person is more likely to follow your instructions.

Guy Barter is Chief Horticulturist for the Royal Horticultural Society (RHS). The RHS is a charity inspiring everyone to grow via its research, advisory, outreach, shows and gardens. For more information, visit:

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