Why Do Garden Plants Turn Yellow?Colin Campbell-Preston
Growing and nurturing plants from seeds to maturity is so rewarding. But since plants can’t communicate with us when something is wrong, if it starts to look unhealthy, it’s often difficult to work out where we’re going wrong.
Yellowing leaves are a signal that your plant is suffering. There are various causes of yellowing leaves, and it isn’t always immediately clear what’s responsible.
These are the most common reason your plants could be turning yellow:
Frustratingly, yellowing leaves could be a sign or over or under watering. Known in the gardening world as moisture stress, if your plant is getting too much or too little water, its leaves could turn yellow.
It can be difficult to work out whether you’re giving the plant too much or too little water, but one way to find out is researching the specific plant species. Some plants prefer drier conditions, so if you’ve been watering these frequently the chances are it’s turning yellow due to over-watering. Other plants need lots of water, so if the soil around them feels dry, it might be a good idea to start watering it more frequently.
Yellowing leaves are a good indication that the plant isn’t getting the right nutrients, or nutrients in the right quantities. Lack of – or too much – nutrients is often a problem with potted plants, as the soil is trapped in its own micro-environment with no outside influence from earthworms, nitrogen fixing plants or decomposing organic material.
Aside from regular watering, plants need nutrients like iron, zinc, potassium and nitrogen, which it cannot produce itself. There are a wide variety of plant fertilisers which provide additional nutrients for the plant – whether you choose chemical varieties or natural options such as bone meal and compost, they will have similar benefits.
However, if your plant’s leaves have started turning yellow even though you’ve been diligently using fertiliser, this may be the problem. Over-fertilisation can result in high concentrations of soluble salts in the soil. This damages the roots by slowing the flow of water and affecting soil pH.
Some plants demand a high level of nutrients, while others thrive in relatively barren soil. Fruit-bearing plants like tomatoes and chillies require a lot of nutrients to feed their fruit yield, while hardy plants and shrubs do not.
Plants need sunlight in order to produce energy. Plants use a process known as photosynthesis to transform produce energy from the sun’s rays. In order to do this, chlorophyll cells in the plant’s leaves absorb the red colours of the light spectrum, reflecting yellow and blue spectrum colours; this is what gives plants green leaves.
If a plant is not getting enough sunlight, this may limit its photosynthesising capabilities. Yellowing leaves may be a sign that your plant needs more sunshine. Garden plants might be too shaded by larger plants or positioning in the garden, while indoor plants may need moving to a more sunny spot, such as on a windowsill.
Equally, a plant that thrives in shady conditions may develop yellowing leaves due to overexposure to the sun. Plants like ferns, hostas and bamboo prefer limited sunlight, so be sure to research what conditions your plant prefers if it starts to show yellowing leaves.
An infestation of pests could be causing your plant to develop yellow leaves. Insects that suck sap from the plant are diverting energy away from it, preventing it from growing and damaging its health.
Pests like aphids, mites, caterpillars and whiteflies are tiny and inconspicuous, so you may be unaware that they have set in until it is too late. Look out for tell-tale signs, like sticky residue on the leaves (this is honeydew – a secretion left behind from pests), dead bugs on the surface surrounding the plant (especially for house plants and potted plants), droppings left behind by caterpillars, and holes in leaves.
Some pests are relatively easy to remove – aphids can be tackled with diluted soapy water for example, while others may require a more intensive strategy. If you find an infestation, try to protect the plants close by ensuring the leaves don’t touch.
The plant’s root system is the most easily neglected area, since it is hidden under the soil and therefore easy to overlook. But if your plant’s leaves are yellowing from an unknown cause, look to the roots.
Potted plants are most commonly stricken with root problems, as they cannot spread out in the soil and begin to choke the pot. Root rot can occur in damp soil, where sections of root are damaged by fungus and begin to die. If your potted plants have yellowing leaves, try repotting them into larger and more spacious pots.
The Capital Gardens team have helped many of our customers solve their gardening problems – if your plants have an issue and you’re not sure how to resolve them contact our team on 0208 348 5054 or visit our homepage.