What are the mophead hydrangeas?
When people talk about hydrangeas, most people mean Hydrangea macrophylla , the so-called “mooseberry hydrangeas”.
This species is available as a flowering plant from January to October in various forms: as pots, tub plants (bushes), hanging baskets, and small trees (standards/pyramids). This article will focus on the most widespread species.
Are hydrangeas hardy?
Yes, they are winter hardy!!!
Of course, there are differences due to different locations and hydrangea species.
In temperate Europe, all hydrangea species are completely hardy – the more sheltered and maritime the location, the better. Therefore, no hydrangea will die outdoors over the winter.
For various reasons described here, the mophead hydrangeas cannot always bring all of their buds to bloom and are therefore often almost only green bushes under unfavorable conditions.
If the location and soil are suitable, they will likely bloom every year, but if the conditions are poor and the plants are not pruned correctly, they will never bloom.
If you have purchased a flowering hydrangea, it should be placed in a particularly sheltered, shady and frost-free location during the first year.
Particularly robust varieties of hydrangeas for safe outdoor use are:
You & Me series , Schöne Bautznerin , Kluis Superba , Otaksa and many more.
The hydrangea is wilting – in the room, on the terrace, in the garden?
What could be the cause? What should I do?
If the hydrangea wilts when it is planted in the garden, it is usually due to a lack of water .
But please don't water in direct sunlight , but rather in the evening. Hydrangeas generally shouldn't be exposed to direct sunlight for long periods, as this can lead to dehydration and leaf burns. These often result from watering in extreme heat.
Measures for wilting leaves in heat:
- Shade
- Keep moist with straw mat or fleece
- Do not use foil!
When it is hot, it is best to place potted plants in the shade, protected from the wind.
If the hydrangea wilts despite the root ball being moist , it is usually due to waterlogging .
This happens if your hydrangea has been watered too much or if there is standing water in the pot, such as after a long period of rain, and the water cannot – or could not – drain away.
A foul smell and brown roots are typical signs.
Such conditions favor fungal infections , which are usually fatal to the plant. Once a hydrangea has wilted due to waterlogging, it's usually beyond repair.
Note: Hydrangeas need a lot of water – but only water when the root ball becomes dry !
Why isn't my hydrangea blooming anymore?
I planted my hydrangea in the garden after it bloomed, and now it's not blooming anymore. My hydrangea is growing, but it has never bloomed.
Common causes: wrong location, incorrect pruning or early frost.
Tips for safe flowering:
- Protected, shady location
- Protect from early and late frosts
- Only fertilize with potassium until the end of July
- Pruning: Only in spring and only on old flower heads – cut back to a pair of buds. Under no circumstances should you cut anything off the hydrangea after mid-June; only cut back flower heads in spring, after new growth, to the next pair of buds.
- Even in winter when the weather is frost-free, keep the soil slightly moist
- After the beginning of August: Stop fertilizing and reduce watering
- From the beginning of September, the hydrangea must literally starve in order to “ripen”, otherwise it will easily freeze
The main cause is incorrect pruning. Before the hydrangea is planted out, it must first reach a certain size.
A freshly planted hydrangea can take up to 1–3 years to bloom.
Tip: A quick, reliable and lush flowering can be achieved if it is first cultivated for a few years in increasingly larger pots outdoors in the summer, or even sunk into the ground, and overwintered frost-free.
The winter quarters should therefore be cool, airy, and frost-free at 1 °C to a maximum of 5 °C (e.g., in well-ventilated sheds or cellars), otherwise there is a risk of botrytis. Light conditions are not important during this time (the dormant period is typical for woody plants).
However, once growth begins in spring, a cool but bright location is important. Even then, the plant must be covered if there is a risk of frost.
Important: The flower buds form at the tips of the shoots in summer – they are vulnerable to frost, especially in autumn. Early frosts in autumn are particularly dangerous, as the buds are still very soft. A sheltered location or protection from early frosts can help.
Another reason is a poor choice of location, i.e. never expose it to the cold, dry east wind.
Ideal: Especially for outdoor plantings, sheltered northern, northwestern, or western locations are ideal. They should definitely be shady to partially shaded. Locations close to heat-radiating house walls, walls, and under trees are also ideal.
My blue hydrangea only blooms pink, has yellow leaves and rotten buds – why?
Hydrangeas grow best in loose, humus-rich, moist (but not constantly wet) soil.
Red, pink, and white varieties require a pH of 5.5–6. Blue-flowering hydrangeas can only be achieved if they were purchased as blue-flowering hydrangeas. The pigment responsible for the blue color of the flowers (delphinidin) can only exhibit its (blue) effect under certain conditions.
Optimal conditions for blue flowers:
- Buy blue flowering variety
- Acidic soil (pH 4.2–4.7) – e.g. with rhododendron or “Hydrangea Blue” substrate
- Low-lime water (preferably rainwater)
- Freely mobile aluminum ions must be present. Therefore, apply Ullmann Hydrangea Blue (aluminum sulfate) as directed for pots, tubs, outdoor areas, and soil mixtures.
Planting tip for long-lasting blue flowers:
- Planting hole 3–4 times the size of the root ball (optimal: 100 liters!)
- Mixture: Use max. 1/3 garden soil + min. 2/3 hydrangea substrate or rhododendron soil or leaf and conifer soil.
- Mix in approx. 2 kg of “ Ullmann Hydrangea Blue ” per m³ of soil
- Check the pH value with your gardener beforehand!
Caution: Red hydrangeas often bloom purple in acidic substrate!
Once new growth appears, fertilization begins again, first with an N-based fertilizer, followed by K and P-based fertilizers. A potassium-based acidic multi-nutrient fertilizer (rhododendron fertilizer) is always beneficial. Under no circumstances should you apply additional fertilizer in late summer (from August onwards) or even in the fall (especially nitrogen), as this will cause the plants to become too mushy and soft, and they will freeze during the first frost. This can also be a reason for flowerless hydrangeas.
Nutrient deficiency, yellow leaves, rotten buds?
Yellow young leaves with green veins: Iron deficiency due to too high pH
→ Remedy: acidic, iron-containing fertilizer, partially replace old substrate with low-lime, acidic substrate, use rainwater
Yellow older leaves (total): Nitrogen deficiency – the deficiency appears first on the older leaves.
→ Remedy: Top up with N-containing complete fertilizer, use humus-rich substrate.
Autumn yellowing: completely normal – an important sign of ripening and bud formation. Hydrangeas are woody plants, and the leaves fall off on their own; never remove them forcefully → risk of fungal infection.
Late frost damage to buds: Young buds that have fallen victim to late frosts appear brown and soft. They are entry points for fungi → remove them immediately!
In the winter quarters: check for air movement and soil moisture. The soil should be only moderately moist, but never allowed to dry out. The soil of hydrangeas planted outdoors should also never dry out – so water lightly every now and then when the weather is frost-free.
Radical pruning to the ground: It may take several years for the hydrangea to bloom again.
Pruning the hydrangeas
When? In spring after new growth begins
What? Only cut back old, dry flower heads
How? Place the scissors directly above the next pair of strong buds. Last year's old, leafless, woody shoots must remain.
Do not cut: woody shoots – this is where the flower buds are located!
Exception: old, frozen wood → cut back to green new growth
Sincerely, your team at Hortensienwelt Ullmann 🌿