I’ve had the pleasure of growing agapanthus, otherwise known as African lilies, in many garden settings in the UK. However, when their striking leaves begin to yellow, some gardeners are left scratching their heads.
Find out the mystery behind yellowing agapanthus leaves, and how to get them back to their verdant green shade.
1 – Seasonal Senescence – A Natural Life Cycle
If you notice yellowing leaves in late autumn or winter, don’t panic. Deciduous agapanthus varieties like Agapanthus inapertus go through a natural dormancy.
Therefore, the yellowing, browning, and eventual dieback is part of their seasonal rhythm.
David’s Tip:
Let the foliage die back naturally. This allows the plant to reabsorb nutrients into the rhizome. Then, only cut back when the leaves are completely brown and crisp.
2 – Overwatering and Poor Drainage
Agapanthus hail from Mediterranean climates, so don’t enjoy sitting in overly west soil. In our wetter UK conditions, especially in heavy clay or water-retentive composts, roots can suffocate from lack of oxygen. Therefore root hypoxia causes yellow leaves, wilting, and stunted growth.
Scientific insight:
Root aerenchyma tissue is vital for oxygen transport. It is a sponge-like tissue found in plant roots, with lots of air space. Saturated soil reduces its function, impairing nutrient uptake.
Also, according to some trials, agapanthus in poorly drained pots is 60% more likely to suffer from chlorosis (yellowing leaves).
What to do:
- First, use loam-based compost like John Innes No. 2 with added grit or perlite.
- Next, ensure containers have multiple drainage holes.
- Finally, raise pots on feet to improve air circulation and prevent waterlogging in winter.
3 – Nutrient Deficiencies – Nitrogen or Iron?
When yellowing occurs across older leaves, suspect nitrogen deficiency. Therefore, if the newest leaves are yellow with green veins, that points to iron chlorosis.
Scientific facts:
- Nitrogen is a mobile nutrient: plants redirect it from older leaves first.
- Iron is immobile: symptoms show in new growth.
- Agapanthus prefer slightly acidic to neutral soil (pH 6.0–7.0). High pH binds iron, making it unavailable.
What to do:
- Firstly, use a balanced liquid feed like tomato feed, which is rich in potassium and contains trace elements.
- For interveinal chlorosis, apply sequestered iron (chelated Fe).
- Also, test your soil’s pH and amend with ericaceous compost if overly alkaline.
4 – Cold Damage in Evergreen Varieties
Evergreen types like Agapanthus africanus are especially vulnerable to frost. Consequently, freezing temperatures rupture leaf cells, causing yellowing, limp growth, and sometimes mushy stems.
David’s Tip:
In colder areas, grow in pots so they can be sheltered in winter.
Also, wrap plants with horticultural fleece or move to a greenhouse.
Eventually, come spring, trim away damaged foliage to encourage fresh regrowth.
5 – Pest and Disease Stress
Whilst generally hardy, agapanthus roots can fall prey to vine weevil larvae, particularly in containers. These white, C-shaped grubs gnaw on roots, leading to nutrient starvation and yellowing leaves.
What to do:
- Initially, tip the plant out of its pot and inspect the roots.
- Then, apply biological controls like Steinernema kraussei nematodes in spring or autumn.
- Ultimately, discard heavily infested plants and clean pots thoroughly.
Expert Diagnosis Table
| Symptom | Likely Cause | Action |
|---|---|---|
| Yellowing in autumn/winter | Natural Dormancy | Let die back naturally |
| Yellowing, wilting, soggy soil | Overwatering | Improve drainage and compost |
| Pale new leaves with green veins | Iron deficiency | Apply sequestered iron |
| Older leaves yellowing first | Nitrogen deficiency | Use balanced or high-nitrogen feed |
| Yellowing after frost | Cold damage | Shelter or mulch, cut back in spring |
| Yellowing and stunted growth | Vine weevil infestation | Use nematodes, inspect roots |
David’s Golden Growing Tips
Agapanthus are native to South Africa, so give them warmth, good drainage, and a balanced diet, to make them feel at home. They’ll reward you with floral fireworks.
- Choose a sunny spot with at least 6 hours of direct sunlight per day.
- Don’t be afraid to let roots get snug in pots; tight quarters promote blooming.
- Water deeply, but only when the soil feels dry at finger depth.
- Deadhead regularly to channel energy into rhizome development.
As with all plants, understanding them means tuning into their natural needs and signs. Yellowing leaves are their way of speaking to us. Whether it’s stress, hunger, or a seasonal snooze.
For more great gardening advice, make sure you head to my YouTube Channel. Make sure you’re subscribed with notifications on so you don’t miss any of my new videos.
Frequently Asked Question
1 – Why do agapanthus leaves turn yellow in winter?
Yellow leaves in winter are often a sign of natural dormancy, especially in deciduous agapanthus varieties like Agapanthus inapertus. This seasonal dieback helps the plant conserve energy in its rhizome. Allow the foliage to die back naturally and only remove it once fully brown and dry.
2 – Can overwatering cause agapanthus leaves to yellow?
Yes, overwatering is a common cause. Agapanthus dislike waterlogged soil, which can lead to root rot and oxygen deprivation. Ensure good drainage by using loam-based compost with grit, and raise pots on feet to prevent sitting in water.
3 – What nutrient deficiency causes yellow agapanthus leaves?
Yellowing older leaves often signal nitrogen deficiency, whilst pale new leaves with green veins may point to iron chlorosis. A balanced liquid feed or sequestered iron supplement can restore healthy foliage. Check your soil pH too, as alkaline conditions can block iron uptake.
4 – How can I protect evergreen agapanthus from frost damage?
Evergreen varieties like Agapanthus africanus are frost-sensitive. Cold snaps can cause yellowing and mushy growth. To prevent this, grow them in containers for easy sheltering, or use horticultural fleece during freezing nights. Damaged leaves should be cut back in spring.
5 – What pests cause yellowing agapanthus leaves?
Vine weevil larvae are a key suspect. These root-munching grubs can trigger yellowing and stunted growth in potted agapanthus. If you suspect an infestation, check the roots and apply nematodes as a biological control in spring or autumn.
David Domoney is a Chartered Horticulturalist, Broadcaster, and Author. David has worked with a number of the UK’s leading garden retailers as a plant buyer and strategic consultant. With more than 30 years experience, in horticulture, David is as passionate about plants now as he was when he bought his first plant at a village fete.
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