Containers: planting up

30-Mar-2015

Containers filled with seasonal or permanent plants are extremely versatile. They can brighten up a corner of the garden, provide handy herbs by the kitchen or make the entrance look welcoming. Yet, life in containers can be tough for plants, so choose the right compost and carry out regular maintenance to ensure they put on a good show.

Suitable for...

Containers are the perfect home for colourful annuals and half-hardy perennials - both of which are sometimes called 'patio plants' or bedding. Most shrubs, climbers, herbaceous perennials, grasses and even trees can be grown in containers. Fruit and vegetables can be successful too, as can some roses.

Choose your container

For containers that need to be outside all year, choose frost-proof terracotta rather than those labelled frost-resistant which can still crack when temperatures fall for long periods.

Imitation terracotta made from plastic or fibreglass are very practical, especially for larger specimens that need to be moved into frost-free conditions as it is lightweight.

Choose containers that are at least large enough to hold the roots of single specimens. Small pots dry out quickly, so plant groups in large containers to help reduce the chore of watering.

Avoid potting a plant (particularly slow-growing types such as camellia or citrus) with a small rootball into a large container: the excess compost can easily become waterlogged, and that can lead to root rot and death. Instead, increase the pot one size at a time.

Ensure adequate drainage by selecting only pots with an adequate size and number of holes in the base. Drill extra holes if necessary.

Where potting media might be washed out of the container, place drainage material over the hole(s) in the bottom of the container, using broken up polystyrene, stones or broken terracotta (crocks). Use a minimum of material as it is important to have as much rooting area as possible.

If possible, raise the container on small blocks or bricks to guard against waterlogging.

Composts

Composts for containers are not the same as garden compost made in your compost bin, but specially formulated for use in pots and often called potting compost or potting media.

Short-term plants: Use a multipurpose compost.

Permanent plantings: Use soil-based composts (e.g. John Innes No 3). To save cost, an aqequate homemade potting media can be made from a mixture of two-parts good garden soil to one-part garden compost. Add a general-purpose fertiliser at the manufacturers' rates.

Lime-hating plants: Use ericaceous composts.

Time-saving additions to compost

You can add water-retaining granules to summer plantings using the dose stated in the manufacturers' instructions.

For permanent plantings or summer colour, consider adding slow-release fertiliser to the compost while planting up.

How to plant up containers
 

  1. Place drainage material in the bottom of the container, such as broken up polystyrene, stones or broken terracotta (crocks). For a container 45cm (18in) deep, a 9cm (3½in) drainage layer is sufficient.

  2. Fill the container with compost, leaving room to arrange the plants on the surface

  3. Carefully remove the plants from their pots, tease out the roots gently and work more compost around the rootballs. Ensure that the top of the rootball is level with the surface of the compost.

  4. Firm the compost around the plants, water well to settle any air pockets and top up with compost if necessary.

  5. Make sure there is a gap of about 2.5cm (1in) between soil level and the top of the container. This will ensure there's room for the water to soak in.


Maintenance

  • Check the compost moisture levels daily from April to September and water if dry. This often means watering once or even twice a day

  • Start feeding four to six weeks after planting, unless the compost contains a slow-release fertiliser

  • From April to September, use a general-purpose liquid feed, unless the compost contains a slow-release fertiliser. Feeding isn't necessary during winter

  • Deadhead regularly to encourage more flowers to form

  • Re-pot in early spring. For permanent displays, repotting is needed at least every two to four years to prevent problems with drying out and waterlogging. In between, top dressing (scraping off the old compost from the top of the container and replacing with new) is useful

  • Reduce watering during winter months 

  • Ideally, prevent the compost from freezing by moving containers under cover or covering them in bubble-wrap

  • In very wet periods, move pots under cover to prevent the compost becoming sodden.

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