Level: Intermediate
Yellow new leaves with green veins most often point to an iron problem, usually iron the plant cannot take up because the pH of the soil or water is high. If older leaves yellow between veins, magnesium is more likely. Check which leaves yellow first, then roots and water, before adding fertiliser.
Key points
- Yellow new leaves point toward iron; yellow older leaves between veins point toward magnesium, but they can overlap [1][6].
- Iron trouble is often not missing iron but high pH blocking uptake [1][4].
- A leaf spray of iron works fast but only briefly, so find the cause [3].
- The sources I read are mostly about greenhouses and landscape trees; the evidence for indoor pots is limited.
What does yellow between green veins mean?
It is called interveinal chlorosis: the tissue between the veins yellows while the veins stay green. Colorado State University Extension describes iron chlorosis as showing first on newer growth with veins staying green [3]. Washington State University HortSense also places iron shortage on new growth, but notes that magnesium shortage can cause the same look [6].
So the pattern alone is not enough; the position matters. Penn State Extension says iron shortage shows on new growth, while magnesium shortage shows first on lower to middle leaves [1]. A Penn State plant science page describes bright yellow lesions between veins on older leaves for magnesium [5]. Note that both pages come from hydroponic or laboratory settings, not home pots.
On a phone, swipe sideways to see every column.
| Clue | Possible cause | Next step |
|---|---|---|
| New leaves yellow between green veins, old leaves mostly fine | Iron shortage or locked-up iron, often linked to high pH [1][3][6] | Check the mix and irrigation water; do not just add more fertiliser |
| Older or lower-middle leaves bright yellow between veins, new leaves fine | Magnesium shortage is more likely [1][5] | Check whether your fertiliser contains magnesium and how old the mix is |
| Whole lower leaves yellow, no vein pattern | Nitrogen shortage, overwatering or ageing [7][8] | See the yellow leaves overview |
| Pale new leaves, uniform colour, dim spot | Low light [7] | Improve light first, then reassess |
| Yellowing plus white crust on soil | Salt build-up or over-feeding [7] | See fertiliser burn |
| Speckles, mites or webbing underneath | Pests can also cause yellowing | See spider mites |
Both shortages can occur together, and damaged roots can block uptake either way. Row one is only more common, not a diagnosis.
How do I tell iron, magnesium and pH problems apart?
At home, work by elimination. First, see whether new or old leaves yellow first [1]. Second, check the roots: if they are rotting or soaked, uptake suffers and extra feed may not help. Third, consider pH and water quality.
Penn State Extension names high pH in the media or irrigation water as the most common cause of iron shortage [1]. Iowa State adds that soil usually holds plenty of iron; high pH stops a tree taking it up [4]. Those sources cover greenhouses and landscape trees, so the principle carries over, but I cannot say that your pot has a pH problem.
- Photograph the yellow leaves and note how long they have been yellow and whether new growth is still yellow.
- Tip the plant out and check the roots; see root rot if they are soft and dark.
- Recall your water, fertiliser and mix. Was lime or dolomite added? Is the water hard or alkaline?
- If you can, measure the pH of the mix with a test kit or meter and follow the instrument instructions. This article gives no home target.
- If still unsure, take photos and details to an experienced nursery or horticulturist.
See also the nutrient deficiency guide and pH and EC.
How can pH drift upward in Hong Kong homes?
Penn State Extension says irrigation water alkalinity above 150 mg/L can raise media pH, causing iron and manganese shortage and a calcium-magnesium imbalance [2]. That is a greenhouse benchmark, not a rule for home pots. I did not find a reliable threshold for Hong Kong home plants, so do not apply that number to your flat.
WSU HortSense also notes that lime leaching from concrete can raise soil pH [6]. On balconies or planters next to cement, look for white powdery deposits. That is a possibility, not a confirmation.
If you use a mix with added lime, hard water or alkaline feed, pH may creep up over time. To know, measure rather than guess.
What should I do step by step?
- Stop adding heavy fertiliser. If pH is blocking iron, more feed may not help and can add salts.
- Rule out root rot, overwatering and low light first [7][8].
- Measure the pH of the mix or ask a professional to test it.
- If pH is high, use an acidifying feed or chelated iron product made for potted plants, strictly at label rates. Do not mix your own.
- For a quick cosmetic lift, a leaf spray is possible, but the source says the effect is often spotty and temporary [3].
- Compare new leaves after a few weeks. Already yellow leaves usually do not fully recover.
Iowa State reports that soil treatments on landscape trees can last two to three years without lastingly changing soil pH [4]. A small pot behaves differently, so rely on observation rather than a timetable.
How is magnesium shortage different?
The classic sign is bright yellow between veins on older leaves [5], and Penn State Extension places it on lower to middle leaves [1]. If older leaves are the ones affected and new growth looks normal, magnesium deserves more suspicion than iron.
The Penn State irrigation page adds that water with less than 25 mg/L magnesium may leave plants short and need fertiliser to supply it, while calcium above 100 mg/L can interfere with phosphorus and magnesium uptake [2]. Again, this is a greenhouse context.
I found no indoor-pot dosage for magnesium, so I give no homemade recipe. Use a labelled plant nutrient product at label rate. If pets share your home, check the safety data and ask a vet.
What should I avoid doing?
- Pouring on more fertiliser at the first sign of yellowing; the iron may be present but unavailable [4].
- Changing water, feed, light and pot on the same day.
- Mixing acids, sulphur or other chemicals yourself. Follow product labels; pesticides in Hong Kong are regulated under the Pesticides Ordinance (Cap. 133).
- Cutting off all yellow leaves at once.
- Relying on leaf sprays alone: the effect may be temporary [3].
How do I prevent it?
- Use a free-draining mix and know whether lime was added.
- Watch water quality and white deposits on the surface, and test pH when in doubt.
- Photograph new growth regularly so you spot interveinal yellowing early.
- Feed at label rates during growth only [8].
- Refresh the mix when roots fill the pot; see the repotting guide.
When should I get help or give up?
If most roots are dark and soft, feeding and pH changes will not help; Clemson suggests discarding plants in that state [8]. If several plants show the pattern together, or new leaves stay yellow after several weeks, take photos and a mix sample to a nursery, horticulturist or laboratory.
Check it step by step with Plant Doctor →
Frequently asked questions
Are yellow new leaves with green veins always iron shortage?
No. Iron shortage is a common explanation [6], but magnesium shortage can cause interveinal yellowing too [6]. Check which leaves are affected and whether the roots are healthy.
Do iron leaf sprays work?
Colorado State says foliar treatment is often spotty and only temporary [3]. Treat it as short-term help and still look for the cause.
Why can a plant lack iron in soil that has iron?
Iowa State says soil usually holds plenty of iron; high pH can stop uptake [4]. That is tree research, so pots may differ in degree.
When should I think about magnesium?
When older leaves are bright yellow between veins and roots and other causes are ruled out [5]. Use labelled products at label rates; do not mix your own.
Will yellow leaves turn green again?
They usually do not fully recover, so judge progress by new leaves. This is general observation, not a claim from the sources.
Sources
- Penn State Extension: “Hydroponics Systems and Principles Of Plant Nutrition: Essential Nutrients, Function, Deficiency, and Excess” — Iron shortage shows between veins on new growth, often from high pH in media or water; magnesium shortage starts on lower to middle leaves (hydroponic and greenhouse setting)
- Penn State Extension: “Interpreting Irrigation Water Tests” — High water alkalinity can raise growing-media pH and cause iron shortage; very low magnesium in water can lead to deficiency (greenhouse and nursery setting)
- Colorado State University Extension: “Iron Chlorosis of Woody Plants” — New growth yellows first while veins stay green; iron is locked up; leaf sprays are temporary; lowering pH has limits (woody plant setting)
- Iowa State University Extension and Outreach: “Pin Oak Chlorosis” — There is usually plenty of iron in soil; high pH blocks uptake; foliar and soil treatments have limits (landscape tree setting)
- Penn State Department of Plant Science: “Magnesium deficiency: nutritional disorders displayed” — Typical magnesium deficiency: bright yellow interveinal lesions on older leaves, sometimes violet-tinged
- Washington State University HortSense: “Common Cultural: Nutrient deficiency” — Iron shortage appears on new growth; magnesium shortage can also cause interveinal yellowing; high pH binds iron; lime leaching from concrete can raise pH
- Penn State Extension: “Diagnosing Poor Plant Health” — Lists common causes for yellow old leaves versus yellow young leaves
- Clemson Cooperative Extension (HGIC): “Houseplant Diseases & Disorders” — Lower-leaf yellowing linked to nitrogen or iron shortage, especially when pot-bound; regular feeding and fresh soil help prevent it
Further reading
- Back to Plant Doctor
- Yellow leaves: causes, how to tell them apart and what to do
- Nutrient deficiency guide
- pH and EC for houseplants
- Fertiliser burn
- Choosing Water for the Plants You Already Have
Sources checked: 31 October 2026. This is general guidance, not an on-site diagnosis. Always follow the product label.
