In spring, lush blooming rhododendrons delight our senses. This annual splendor requires an evenly dosed supply of nutrients. Fertilize rhododendrons – do it right! More about the basics for he althy evergreen plant growth
How do you fertilize rhododendrons correctly?
To properly fertilize rhododendrons, it is best to use organic fertilizer or special rhododendron fertilizer in the months of April to October. Avoid calcareous fertilizers and ensure there is sufficient water supply. Compost and dried coffee grounds are also suitable as organic fertilizer.
In order to support good growth of rhododendrons, correct fertilization plays an important role. Because the root system of rhododendrons branches widely on the surface, nutrients must be immediately absorbable in the soil. To fertilize rhododendrons, it is best to use organic fertilizer or special rhododendron fertilizers.
But compost, leaves and coffee grounds also provide the plants with organic nutrients. The use of organic fertilizer also prevents over-fertilization.
The most important thing when fertilizing rhododendrons
Avoid fertilizers that are enriched with lime, such as primary rock powder. In addition to a pH value that is too high, most rhododendron varieties react sensitively to calcareous soils. On the other hand, like all shrubs, they appreciate mulch in loose soil.
Best fertilization time and dosage
Rhododendrons, which are ideally placed in partial shade without waterlogging in slightly acidic soil, benefit considerably from the right fertilizer. Even if the location or soil does not offer ideal conditions for these easy-care ornamental shrubs, good fertilizer compensates for the disadvantages. From April to October is the best time for an evenly dosed food intake.
Caring for ornamental trees naturally means meeting special requirements in terms of location and nutrient supply. How much fertilizer depends on the size of the plant and leaves. As a rule of thumb, the following dose per square meter applies:
- Specimens up to 60 cm – 40 to 60 grams
- Specimens from 60 to 120 cm – 90 grams
- Specimens over 120 cm – 120 to 200 grams
Work the first low-s alt sustained release fertilizer loosely into the top layer of soil under the outer third of the leaf crown. An additional addition of horn shavings at 50 - 70 grams per square meter promotes deep green foliage and the formation of abundant flower buds. Good to know: Do not fertilize freshly planted rhododendrons directly. But only next spring, when the shrub has strong roots.
Refertilization after rainy months
Refertilizing rhododendrons is recommended at the beginning of July. Especially the depleted soil after a rainy spring allows you to fertilize at a rate of 30 to 50 grams per square meter. For small-leaved rhododendrons, half the fertilizer is sufficient. Don't forget: water plants sufficiently after each nutrient application.
Yellow leaf alarm – high time for special fertilizer
Rhododendrons that grow, green and bloom need trace elements, magnesium, nitrogen and phosphorus. Yellow colored leaves are an alarm signal for acute nitrogen deficiency. which requires immediate care so that the plant can grow he althy green again.
Compost and coffee grounds as organic fertilizer
Regular additions of compost never hurt. The soil stores moisture better, remains loose and nutrient-rich.
Coffee grounds contain phosphorus, potassium and nitrogen. All three have a metabolism-activating effect. You can either add fresh coffee grounds to the watering water or distribute them directly around the plant. Because fresh coffee grounds mold quickly, you have to dry them on a plate or tray first. Leftover dried fertilizer will last for several months in an airtight container.
Potting soil mixed with coffee grounds is ideal for potting a mini rhododendron. The slightly acidic pH value of coffee neutralizes soils with too high a pH value and calcareous irrigation water. It also repels some pests.
Fertilize large-scale rhododendrons yourself – but how?
In older, large rhododendron areas, the pH value of the soil is often above pH 5. Therefore, the first thing we recommend is a soil analysis using test sticks from a gardening store.
Sprinkling 200 grams of uncleaned sulfur flower (€12.00 on Amazon) per square meter lowers the pH value of the soil surface. This is available in drugstores or gardening companies. This is followed by fertilizing with a special organic-mineral rhododendron fertilizer classified 8 – 5 – 8 – 3. Around 100 grams per square meter.
From mid-April you can support with an inexpensive application of blue fertilizer. At the beginning of the planting period, the growth of the giant rhododendron with 60 grams per square meter. Important: Add 40 grams of kieserite per square meter to each fertilizer to ensure an optimal magnesium supply.
Tips & Tricks
You can fertilize with coffee grounds all year round. To make a super fertilizer, mix coffee grounds with horn shavings and spread lawn clippings on top. This saves money and waste.
