For Rhododendrons azaleas and camellias I always use a specialised fertilizer from miracle-gro which has the right balance of nutrients at the right concentration to support flowers. With a specific fertilizer you can easily avoid adding too much nitrogen with various fertilizer and take out the guess work to ensure the rhododendron can flower. If you have lots of foliage and no flowers and you have used a lot of fertilizer, just leave the rhododendron to recover for a year without adding any fertilizer and if the plant is healthy it should flower the following year and form flower buds.
Frost damage is often a problem with plants such as rhododendrons which form next years flower buds usually from around August after this years display of flowers. It is usually a late frost in the Spring as the flowers begin to emerge that turns the flower buds a brown colour which of course prevents flowering.
The leaves of the rhododendron can often tolerate the frost but the flower buds are still vulnerable. However in climates that experinece freezing temperatures in Winter it is a good idea to plant or transplant your rhododendron in a relatively sheltered area of the garden such as under a tree in a corner with some protection. Rhododendrons that are out in a open area are at higher risk of suffering frost damage to their flower buds. You can also mitigate some damage with the use of horticultural fleece to protect flower buds before a late frost occurs, however I find it is more practical to find a sheltered planting area for your rhododendron.
Rhododendrons requires well draining yet moist soil to grow and flower. If the soil is too dry then the plant is stressed and the flowers buds do not open in the Spring.
If your rhododendron has suffered significant drought stress then it may not flower this year however this can be easily addressed so that it flowers well the following year. The solution is to add a layer of mulch around the rhododendron to help conserve water, add nutrients to the soil and improve the soils structure. Apply a 1 inch thick layer of compost, leaf mould or well rotted manure to the surface of the soil around the rhododendron.
Organic materials such as compost, leaf mould or manure have an exceptional capacity for retaining water which helps to keep the roots cool and the rhododendron hydrated so that it can flower. Ensure that the soil stays consistently moist throughout the growing season so the plant can flower by testing the soil to a fingers depth to detect moisture.
They are rarely seen and will drop to the floor if disturbed with a torch at night. They are always female and can lay up to eggs per year in the soil at the base of the plant. During the autumn and spring months these eggs develop into small white semi-circular grubs growing to about mm in length, with a red head.
It is these grubs which feed on the tasty soft roots of rhododendrons, and they can eat all the bark away from the main stem just at or below compost level.
This is usually terminal and the plant collapses, often quite quickly in the spring. The white grubs pupate into adults during warm spring weather and the life-cycle starts again. All plants that we produce are treated against vine weevil using natural nematodes at the propagation stage, and all our potting compost is treated to kill any grubs in the pots. We also treat for adults during the summer months, and we regularly apply millions of nematodes to our crops from spring until autumn.
We are confident that our plants leave here inoculated against vine weevil damage. The best time for preventative treatment is April before hatching and early September before winter. For further advice, please refer to up to date recommendations from the RHS: www. Caterpillars can feed on rhododendrons, sometimes dropping off overhanging trees onto the foliage, where they make notches on leaves which can resemble vine weevil damage. However, caterpillar notchings are more gentle and not as jagged, and sometimes even in the middle of the leaf.
This is fairly cosmetic damage, and caterpillars do not kill the plants like vine weevil. Rhododendron lace bug is closely related to the better known Pieris lace bug. It is a mm long sap-sucking insect with a faintly marked but mainly transparent lace-like wing, and a darker line across the wings near the base. It marks rhododendron leaves with unsightly pock-marked yellowish spotting on the upper surface during the summer.
Adults, cast skins, and brown excrement can be found on the undersides of affected leaves. Treatment is best carried out in early summer when the newly hatched nymphs are present, but further treatment may be required. Use a good organic or chemical insect spray after the flowering season.
Cushion scale is a sap-sucking insect that attacks the leaves of evergreen plants such as rhododendron and camellia. They lay eggs in spring and summer on the undersides of leaves in what looks like woolly socks. This is a waxy mass of eggs up to 10mm long and mm wide which can persist through the year. Insects develop from the eggs and excrete onto the upper surface of leaves below, creating sooty mould , a fungus which develops over the winter months especially under greenhouse conditions.
On small plants, this mould can be cleaned with a cloth and soapy water, and then spray with an organic or chemical control after flowering to control the nymphs in early summer. Leaf-hoppers are easily found on affected plants from July to August, by brushing against rhododendron foliage. This will disturb the brightly coloured leafhoppers which will hop onto a nearby leaf, a bit like a grasshopper.
They are mm long, with pale yellow heads and bluish green thorax. The wings are folded along the body and are also bluish green, with 2 orange stripes.
The incisions into the bud, allow the fungal disease bud blast See 4. However, recent research is now questioning this link. It is noticeable that R. Adult leaf hoppers are easily controlled with a good organic or chemical spray, though this should be directed under the leaves, and several applications during the summer may be necessary. Rhododendrons are fairly unpalatable and can be poisonous to sheep and dogs stupid enough to eat foliage in large quantities , so damage by animals is not usually a problem.
Rings of chicken wire around vulnerable plants or new borders for a few years will normally offer sufficient protection.
Deer are selective feeders, but if they find something they like, they will keep coming back to it that season. We have deer through our property the whole time but have found they only like grazing the following types up to a height of about 75cm: Camellias, evergreen azaleas, a few small leaved R.
Rabbit populations go up and down depending upon myxomatosis, but they can eat the young foliage on evergreen azaleas and dwarf rhododendrons when there is little else for them to eat. Pets and children! Some varieties are much more brittle than others, eg Stenopetalum Linearifolium and nakaharai azaleas. If pets repeatedly use the same area as a toilet, this can create toxicity which shows as scorched leaves.
If your Rhododendron isn't flowering and you can see some black buds, this could be either frost see 4. If the problem is frost, the buds will be brown or black and smooth, and whilst a little unsightly, it is the result of weather conditions.
If this happens regularly, it may be best to select a hardier variety more suited to your locality. Bud blast shows as small black hairy growths like a hedgehog! It is a fungal disease which turns the flowering bud mouldy over winter and prevents flowering. It is spread by leaf hoppers see 4. They have been seen in greater numbers in recent summers. Some varieties are affected more than others, but this varies from garden to garden.
Certainly some mauves seem worse, and those more associated with R. To control bud blast it is best to pick off and destroy as many infected buds as possible, clear out dead branches, and prune back other trees and shrubs to allow free air movement in and around the plant. Bud blast is reduced when leaf hoppers are reduced, though recent research is challenging this link.
We recommend organic controls such as SB Plant Invigorator which coats the foliage with a soapy solution and prevents the leaf-hopper from feeding. Several applications may be needed to control different generations from June to September. Dual action fungicide and insecticide sprays are also recommended. Powdery mildew was a considerable problem to certain groups of rhododendrons around Plants such as R. Nowadays, the most prone varieties are not grown, and plants seem to have developed greater resistance so the disease is not the problem it once was.
Powdery mildew fungi produce microscopic air-borne dispersal spores which have a high water content, enabling them to infect under drier conditions. Powdery mildew is associated with water stress and is characterized by dark brown or black spotting on the upper and lower surfaces of the leaf. Marks are usually round, and often have a paler halo on the outside. The powdery white fungal spores can sometimes be seen on the leaf underside.
Left untreated, these can spread across large areas of the leaf, weakening the plant, and causing leaf drop and plant death.
Layering rhododendrons involves taking a low-growing branch and pegging it to the ground so it can take root. This is best done in late-summer. There are no pests affecting rhododendrons.
However, the fungal disease rhododendron leaf spot can affect the leaves, causing them to drop. Rhododenron ponticum is on the invasive plant list, so should not be planted in gardens and should be removed where possible.
Sometimes rhododendrons stop flowering. Find out why, and how to resolve the problem, in our Quick Tips video:. Rhododendrons sometimes succumb to over-watering. However, under-watering can also kill rhododendrons. Other reasons for sick or dead rhododendrons include planting too deeply remember rhododendrons are shallow-rooted and applying too much fertiliser.
Then, prune away damaged stems. Water sparingly and apply an ericaceous liquid feed as the flower buds are developing in spring, only. This charming hardy climber creates a canopy of glossy green foliage, which in summer is strewn with flat white panicles of flowers on long stems. Add colour to your garden this winter, select from pansy 'Colourburst', 'Grande Fragrance', wallflower 'Wizard' and viola 'Valentino'. A superb evergreen bearing delicate, waxy, bell-shaped flowers in the depths of winter, with lush green foliage for year-round interest.
Home How to Grow plants How to grow rhododendrons. This review contains affiliate links and we may receive a commission for purchases made. Please read our affiliates FAQ page to find out more. How to grow rhododendrons — where to plant rhododendrons.
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