Japanese azaleas and rhododendrons transform every shady garden into a Garden of Eden throughout the summer with an abundance of flowers. This apparent contradiction between flourishing display of splendor and a shady location always arouses astonished looks among hobby gardeners. Nevertheless, imposing rhododendrons and the small Japanese azaleas belonging to the same genus feel extremely comfortable in the shelter of tall trees. With regard to further demands on their cultivation, the flower wonders also do not move on the well-trodden paths of other ornamental plants in the garden. The following care instructions provide detailed information on which aspects are involved and how they are handled.
Table of Contents
- Plant family of the heather family (Ericaceae).
- Scientific name of the genus: Rhododendron.
- Growth heights between 200 cm and 500 cm.
- Scientific Name Japanese Azalea: Rhododendron japonicum.
- Growth heights from 40 cm to 50 cm.
- Hardy, deciduous or evergreen.
- White, pink, red, yellow and purple flowers from April to August/September.
- Emit a delicate to intense fragrance.
- All species and varieties are poisonous plants
- Trivialname: Rosenbaum
Although Japanese azaleas belong to the genus Rhododendron, there is a difference between the ornamental trees. While rhododendrons are only cultivated in the garden, Japanese azaleas also adorn the home as pretty houseplants.
In order to offer Japanese azaleas and rhododendrons optimal living conditions, it is worth taking a look at the climate of the native regions of Southeast Asia and the temperate zones of Europe. Here they thrive in the light shade of the coniferous and deciduous forests and along sheltered mountain slopes. The more precisely these location constellations can be simulated in the home garden, the more vigorously the flowering shrubs will develop.
- Partly shaded location in the shelter of tall trees.
- The wetter the soil, the sunnier the location can be.
- However, direct sunlight at midday has a negative effect.
- Avoid wind-exposed planting sites as much as possible.
It shouldn’t be too dark for the rose tree, because in such conditions the willingness to flower decreases significantly, while at the same time the compact growth habit is lost.
In the natural range of rhododendrons, it rains so often that a layer of humus just a few centimeters thick is enough for them to take water and nutrients from it via a shallow root system. Of course, this is only possible because the humic substrate is extremely acidic with a pH of 4.0 to 5.0. In neutral or even alkaline soil, the nutrients would be too bound due to the lime content to be used by the ornamental trees.
- Permeable, loose, humus-rich soil.
- Acidic soil, with as little lime content as possible.
- Evenly moist potting soil without waterlogging.
Since a pH value of 6.0 and above in Japanese azaleas and rhododendrons inevitably triggers growth depression and is considered the cause of chlorosis, it is advisable to carry out a test at the preferred location. Corresponding sets are available in specialist shops and on the Internet for less than 5 euros and can be used without any prior knowledge of chemistry.
Although rhododendrons in the vicinity of garden ponds or streams give hobby gardeners a lot of joy, it should not be concluded from this that they require a particularly high amount of water. True, due to the lush biomass, especially during flowering, they evaporate a corresponding amount of moisture; which, on the other hand, does not qualify them as ericaceous plants in the true sense, as is commonly erroneously claimed. The only thing they have in common with such plants is their low pH.
- Water evenly but moderately.
- Water daily as needed during dry summer periods.
- Preferably use low-lime rainwater or pond water.
- Water directly at the root ball and not over the leaves and flowers.
Especially in the year of planting there is a higher water requirement. At this time, the fibrous root system is still growing and not very well established. Knowledgeable gardeners are aware of this and take this fact into account by doing a thumb test on every tour of their green kingdom to determine whether an additional dose of water is required. If the surface of the earth has dried, the watering can is used immediately.
Japanese azaleas and rhododendrons have a comparatively high consumption of nutrients, such as nitrogen, phosphorus, potassium and trace elements, especially during the growth phase from April to October. Since the natural supply in the soil in the home garden is rarely sufficient, prudent hobby gardeners compensate for an undersupply by administering organic or mineral fertilizers, or a combination of these, to their carnation plants.
- Apply a starter fertilizer in March in the form of compost or rhododendron fertilizer.
- Administer a preparation with a depot effect for 6 months or a storage fertilizer for 2-4 months.
- Optionally every 2 weeks, lightly incorporate mature garden compost and horn shavings.
Mulching with coarse horn shavings or grass clippings has proven to be best. Applied repeatedly, the mulch material supplies the plants with nutrients, keeps the soil moist longer and suppresses weeds.
Ornamental trees, such as rhododendrons, are grateful after flowering if you clean off all withered parts of the plant. This measure has several advantages: The formation of new buds is promoted. Power-sapping seeds cannot even develop. Shoots and branches are encouraged to branch out even more, for the benefit of a compact, dense habit.
- Grasp the young twig below the withered blossom with one hand.
- Break off the flower with the other hand so that the new shoot is not damaged.
- Always tear off unwanted wild shoots at the base of the exposed root neck.
In the same operation, dead branches or those with sparse foliage are completely thinned out. As a result, light and air can reach all areas of the flowering bush again, effectively preventing bare growth. Rhododendrons are also receptive to a light topiary at this time. Then there is a good chance that the shrub will bloom again in its old glory next season.
Japanese azaleas and rhododendrons do not receive regular pruning. The hobby gardener only uses scissors when the flowering shrubs threaten to become bare.
- The best time to cut back is in March.
- Cut the ornamental shrub no deeper than 50 cm to 60 cm.
- Splitting the cut over 2 years reduces the stress significantly.
Rose trees are remarkably pruning tolerant. Even thick branches can be trimmed with a saw and will sprout out of their dormant eyes over the next few years. The jagged cuts are ideally smoothed out with a knife and then treated with a wound closure agent. However, a little patience is required. The more radical the pruning, the more time Japanese azaleas and rose trees take to sprout again.
A radical pruning undoubtedly puts a strain on the flowering beauties. As a result, attentive hobby gardeners give their azaleas and rhododendrons special attention in the years to come. An extra portion of nutrients, plenty of rainwater when it’s dry and a fresh layer of mulch quickly replenish the botanical power reserves, paving the way for a lush new start.
Thanks to the robust winter hardiness, there are basically no special precautions to be taken for overwintering. Only when there is a frost is there a risk of damage to evergreen rhododendrons due to drought. For protection, the plants roll up their leaves to reduce evaporation. However, if the ground freezes, the flat-rooted plants can no longer get fresh water. The prudent hobby gardener protects the ornamental shrubs with reed mats and fir branches as a preventative measure. He also uses frost-free days to water the rose trees.
If you want more specimens of the charming large and small ornamental shrubs, you can choose from various methods of propagation.
The best candidate for this form of propagation is a not too young, strong, healthy rhododendron that has flexible side shoots.
- Pull the chosen branch to the ground and mark the spot.
- Loosen the soil with a rake and work in the compost.
- Using a razor blade, cut a 15cm notch in the bark.
- Hold the wound cut open with a match.
- Place the sinker in the gutter, cover with leaf soil and fix.
- The leafless tip of the shoot is still sticking out of the ground.
Tied to a small wooden stick, the tip of the sinker maintains its upright posture. When the shoot begins to grow, this is the signal that a new root system is emerging. The following spring, the time has come to separate and dig up the weeder from the mother plant. Immediately afterwards, the Japanese azalea is planted at the new location.
Several 15 cm to 20 cm long, semi-lignified cuttings are taken on an overcast, mild day in early summer. Completely green cuttings are too soft and immature to root alone.
- Remove all flowers and defoliate the lower half of the cuttings.
- At least 3 to 4 thickened leaf nodes must be visible.
- Fill a pot with a peat-sand mixture or special potting soil.
- Plant the cuttings individually halfway into the ground and moisten.
- In a bright, warm place keep the substrate slightly moist with rainwater.
- The roots protrude from the water drainage hole and are repotted.
A plastic bag pulled over it exerts a positive influence on propagation by creating a warm, humid microclimate underneath. At the same time, the hood keeps insects from laying their eggs in the substrate. The warmer the chosen place during propagation, the faster the rooting of the pot proceeds.
The young plants from self-propagation or bought ready-made in the garden center are planted in April/May or in autumn. Successful planting depends critically on soil preparation. So that the shallow roots find a soil that is as humus-rich as possible, acidic leaf or coniferous soil, compost and horn shavings are worked in to improve it. If the planting site is under pine or oak trees, the preparatory work is reduced to loosening the substrate.
- Dig planting holes from 30 cm to 50 cm deep and four times the ball diameter.
- Create a drainage made of gravel or potsherds at the bottom.
- Plant rose trees in acidic bog soil and water generously.
A pouring rim that slopes slightly towards the root neck improves the utilization of irrigation and rainwater. Finally, if the experienced hobby gardener spreads a thick layer of mulch, Japanese azaleas and rhododendrons quickly feel at home.
The cultivation of rhododendrons and Japanese azaleas is by no means as demanding as the flowering shrubs suggest at first glance. If their demands for an acidic, humus-rich soil are met, combined with an adequate supply of water and nutrients, half of the way is already done. In addition, the location should be in the light shade of high deciduous and coniferous trees so that the heather plants quickly feel at home. If the expert hobby gardener protects the enchanting ornamental trees from the blazing midday sun and calcareous soil, nothing should stand in the way of an annual festival of colors.