Contrary to what some might think, rhododendron can grow beautifully in containers. You can transfer the plant to a cooler, shady spot on a hot summer day. When the plant is in full bloom, you can show it off on your patio or near the front door of your home. By growing your rhododendron in a container, you can be a doting plant parent, and create all the right soil and sun conditions to keep it healthy and beautiful for years.
Select dwarf varieties of rhododendrons when planting in containers. Look at hybrid varieties such as the pink flowering yaks (R. yakushimanum) that bears pink and white flowers, or the Rhododendron lutescens for light-yellow blooms and new leaves that start off red. Give Ostbo's Red Elizabeth a try to enjoy vivid scarlet-coloured blooms in the spring and the autumn.
Find a container with drain holes on the bottom. Use a 30 to 35 cm (12 to 14 inch) container for a 4.5 litre (1 gallon) plant or a 40 to 45 cm (16 to 18 inch) container for a 22.5 litre (5 gallon) plant. Buy a set of pot "legs" to keep the plant from sitting in water and a plate to catch water from the pot's drain holes.
Use mesh screen material to create a barrier on the inside of the pot, over the drain holes, to prevent soil erosion and insects from crawling into the soil. Opt for this method, versus gravel, which has a tendency to make the plant leggy by becoming waterlogged, which is often the very reason why a rhododendron ceases to thrive in a container.
Fill the container with a good-quality potting soil or a mix formulated for azaleas and camellias. Plant the rhododendron into the container and keep the top of the root-ball slightly above the soil level so the trunk doesn't get buried. Top the soil with mulch to keep the plant cool in the summer and keep the topsoil from drying out.
Determine when to water by sticking your finger in the soil. Water thoroughly when the soil is dry to the touch.
Apply a fertiliser formulated for rhododendrons in spring. Use half of the recommended rate because container plants require less fertilisation that those in garden beds, and overfertilizing can make the leaves grow before the flowers. Continue to fertilise until the August. Feed plants that will winter outdoors once each month to improve the plant's cold hardiness and immune system, or bring plants indoors and cease fertilising until spring.
Prune and pinch flower tips to encourage the rhododendron to grow bushy and compact. Prune more extensively to revitalise a plant that exhibits any leggy growth. Do not cut branches back to the wood because as a rule, rhododendron will not produce new shoots. Remove spent flowers to keep the plant neat and clean.
Repot the plant every other year and work in one part potting compost with three parts garden mix for azaleas and camellias to keep the soil loose and porous. Examine the roots when you repot. Trim up to one-third of the roots if they are leggy and also to allow room in the container for the potting compost.
Ask at a nearby garden centre for advice on dwarf rhododendron varieties that grow best in your area.