They are popular garden plants that delight with a rich abundance of flowers for many years. Even without flowers, the evergreen trees are decorative and have a harmonious growth and lush green leaves. When planting, pay attention to the optimal soil conditions and location. The popular ornamental trees thrive on acidic, humus-rich soil and in light shade and grow slowly.
Useful information Location Planting Care Watering Fertilizing Pruning Overwintering In the tub Pests & Diseases FAQ
Worth knowing about rhododendrons
Botanical name: rhododendron hybrids, R. Yakushimanum hybrids
Other names: rhododendron, alpine rose
Use: flowering shrub, shade -tolerant flowering shrub
Origin: Asia and North America
Flowering period: April to June depending on the variety and location
Flower colors: violet, pink, red, white, yellow, blue
Special features: popular garden plant with high demands on soil conditions and characteristic, evergreen and decorative foliage. Harmonious in growth without pruning and robust against diseases and pests. Also available as standard or dwarf varieties.
In which location does rhododendron feel most comfortable?
The ideal location for most species is characterized by a high relative humidity in the semi-shade. Dry heat in summer is not optimal for the heather plant, so a garden spot in the light shade or a location on the north side of a house is suitable. It is important that it is bright and sheltered from the wind. If it is too shady there, the plant grows loosely and the formation of flowers is greatly reduced.
How do I plant my rhododendron in the garden?
The best care starts with the right planting. Rhododendrons can be planted in the garden all year round. Spring is the best time for planting to give the plants enough time to root before winter. Thorough soil preparation is important when planting. The planting hole is dug to a depth of 40 to 50 cm. Make sure there is good drainage, ie if the soil tends to become waterlogged, you should put 5 to 10 cm of gravel or expanded clay drainage in the planting hole. A planting hole three to four times the size of the ball is recommended for rapid growth. Before planting, water the plant thoroughly and place the root ball in the planting hole. Do not plant deeper than the top edge of the root ball and fill up the planting hole with high-quality special soil.
Our gardening tip: dimension the planting hole large and use plenty of special soil. This is how you offer the rhododendron the best starting conditions!
How do I care for my rhododendron with bark mulch?
A mulch layer of 2 to 3 cm of bark keeps the soil around the heather plant moist for longer and prevents unwanted weed growth in your garden. The ideal time to spread the bark mulch is early spring or in autumn as winter protection. Another option is to plant groundcover perennials such as Waldsteinia. These also keep the soil moist and bring additional color with their flowering. Our gardening tip: Alpine wild varieties such as Rhododendron ferrugineum are suitable for sunny locations. The group R. yakushimanum hybrids can also cope with more sunlight, but sufficient soil moisture is important here.
How do I water my rhododendron?
Freshly planted rhododendrons need additional water in phases without precipitation. It is important not to water a little every day, but to give larger amounts of water at intervals. This can vary depending on soil conditions, temperature and plant size and it is not possible to make a blanket recommendation. Demand-oriented watering is particularly important in the first year after planting.
If the rhododendron has been firmly rooted in the ground for years, additional watering is only important in extremely dry phases. Our gardening tip: If the leaves are limp and curled up, the plant should be watered. Curled leaves in winter can also be a sign of winter protection. In this way, the plant reduces evaporation and protects itself from severe frost.
How do I fertilize my rhododendron?
Proper care with the right fertilizer is very important for healthy plants with lush flowers. The fine fibrous roots are anchored flat in the ground and do not go very deep into the ground. It is therefore important that the nutrients are immediately available. With special fertilizer, the needs of the alpine rose are optimally met. You can fertilize for the first time in April/May. You can fertilize the second time after flowering in July/August. It is important that the granulated special fertilizer is never put directly into the planting hole, but is always applied to the surface and gently worked in. The soil should be moist or watered after fertilization.
Our gardening tip: Pale yellow rhododendron leaves are a sign of a lack of fertilizer. The pH of the soil can also be too high, which means that the nutrients cannot be absorbed by the plant. Here it is advisable to take a soil sample and check the pH value.
How do I prune my rhododendron?
A regular cut is not necessary for the hybrids. Plants that have grown too large do not have to be cut and can therefore be brought back into shape easily and well without cutting. It is best to prune your rhododendron immediately after flowering to give the plant enough time to grow in summer. The new shoots mature before winter. In the first year you can cut about half of the branches. Then cut the other half in the second year. If you cut too hard, the plant will not flower for one to two years.
Breaking out wilted rhododendron flowers:
The bursting of the inflorescences immediately after the rhododendron blooms promotes the formation of new buds, and no seeds are formed, which means that the plant’s energy is wasted. When breaking out, make sure that the new shoots are protected and consistently remove the old flowers by hand. Scissors are not necessary for this.
How do I overwinter my rhododendron?
Rhododendrons are perennial shrubs and can bring joy with a rich blessing of flowers for many decades. The winter hardiness is very much dependent on the variety, the soil conditions, the nutrient supply and the temperature profile in winter. Rhododendron roots lie very flat in the ground and are therefore easily damaged at low temperatures. A layer of mulch can help.
With permanent temperatures below -10 °C, sensitive varieties should be protected with brushwood or fleece. This measure is particularly important when the sun is shining and the ground is frozen, because as an evergreen plant there is continuous evaporation. This results in drying out due to a lack of water supply.
How do I plant my rhododendron in a pot?
In order to be able to enjoy the fascinating plants without a garden, rhododendrons can be planted in large pots and tubs. Basically, rhododendrons in pots have the same requirements in terms of location and soil as planted specimens. It is important that the soil moisture is kept even and that there is neither waterlogging nor dry bulbs. With a little finesse, the rhododendron culture in the pot succeeds. It is watered with low-lime rainwater. When overwintering, it is important that the rhododendron in the pot receives sufficient winter protection with fleece or other materials and that it is also watered in winter if necessary. Dwarf forms or R. yakushimanum hybrids are particularly suitable for pots, with compact growth and a good form in pots over a long period of time.
What pests and diseases can the rhododendron get?
With the right site conditions and need-based fertilization, rhododendrons are very robust. Plants that suffer from water stress, too much heat or a lack of fertilizer are more susceptible to diseases and pests. Below are some possible problems with rhododendrons.
Frequent leaf lightening due to lack of fertilizer or too high pH.
Leaves are curled up and entire shoots are dying. Occurs especially when there is waterlogging in summer. If possible, keep drier and generously remove affected branches.
The buds will turn brown and die over the winter. A fungal pathogen is usually responsible. This is transmitted via a sucking insect, the so-called rhododendron leafhopper. Possible control measures are yellow boards to catch the cicadas and a preventive treatment of the plants with a plant cure. The plant’s own immune system is strengthened in a natural way and the spread of pests is minimized.
From May onwards, the vine weevil beetles cause semicircular bay damage on the leaves. This damage is caused by the bug and is initially just a visual nuisance. Worse is the damage the larvae cause to the roots. The plants become limp, stop growing and can even die. Biological opponents are used to combat the larvae. So-called parasitic nematodes are easy to use and effective.
The approx. 10 millimeter large, green insect sucks on the underside of the rhododendron leaves from May. The suction does relatively little harm. The problem only arises in autumn when the cicada lays its eggs. The cicada cuts small slits in the buds, spreading a damaging fungus. As a result, the buds do not sprout in the coming spring, the buds turn brown and the fungus continues to spread. Affected buds are generously broken out and disposed of. Yellow boards catch the rhododendron planthoppers well and thus egg laying is prevented.
FAQ — Frequently asked questions about rhododendrons
What special soil requirements does the rhododendron have?
The rhododendron feels at home on humus-rich and well-drained soil. As shallow roots, the plant species cannot root well in compacted soil, and is therefore limited in root growth and takes care of itself. A location with loose soil with a pH between 4.3 and 6 is ideal. If the pH is too high, the soil should be changed before planting, because too high a pH will result in chlorosis (yellowing of leaves and stunted growth).
Acidic soil: For all rhododendrons it is optimal if the soil has a pH of 4.3 to 6. If the location is too alkaline, certain nutrients cannot be absorbed. With rhododendron earth, the soil can be significantly improved when planting.
Why is my rhododendron blooming sparsely?
Possible reasons for a low abundance of flowers on rhododendrons can be:
- fertilizer shortage
- heavy cutback
- Infestation with rhododendron planthoppers
Location is not optimal, so lack of light can lead to low bud formation.
With which plants can rhododendrons be combined?
All plants that have similar demands on soil and light conditions are ideal for combining with rhododendrons. Good plant partners are: ferns, hostas, lady’s mantle, hydrangeas and many more.
At what distance are rhododendrons planted?
The planting distance depends essentially on the species and variety. Since the growth height depends on the variety, the planting distance varies and there is no general information.
Why does my rhododendron have yellow leaves?
Yellow leaves can be a result of a lack of nitrogen or too much or too little water. Check the site conditions and have a soil analysis carried out if necessary. This gives you information about the fertilizer content in the soil and the necessary care measures.
Why does my rhododendron have a bone pattern on the leaves?
Light-colored leaves with a bone pattern are often a sign of missing iron. Often the original cause is too high a pH value. This means that the iron present cannot be absorbed. Therefore, you should first have the pH value determined and, if necessary, fertilize with special iron fertilizer. Furthermore, the irrigation water should be as soft as possible.