Written and edited by Tammy 6th March 2025
Diagnosing what’s wrong with a sick or dying plant can be tricky stuff, they can exhibit a whole host of symptoms that may indicate different underlying issues.
Environmental conditions, pest infestations, nutrient deficiencies, and diseases all come into play so having an understanding of these elements really is important to be able to diagnose a sick plant successfully.
Just as doctors ask questions, listening for clues and observing the physical symptoms, so do I when faced with an unhappy plant.
Each symptom can tell a story about the plant's condition and the potential problems it faces. Yellowing leaves might suggest overwatering or nutrient deficiencies, while brown, crispy edges could indicate underwatering or environmental stress.
It can be a complex puzzle, and by no means do I profess to have all the answers, but it's those challenges that I enjoy every day.
Possible reasons your plant is sick
There are three different possible scenarios, a pest, disease, or a disorder.
Definitions:
Pests- Insects, mites, rodents, animals.
Disease- A fungal, viral or bacterial infection.
Disorder- Abnormality in the way a plant is growing as a result of incorrect or inconsistencies in water, nutrition or exposure to climatic and soil conditions.
What to look for
Evidence of pests
Pests eat plants. Sometimes the clues they leave behind can be obvious while other times not so much. Different sized insects and animals AKA 'Pests', leave different evidence of their feastings behind.
Mites are microscopic, (barely visible to the naked eye) sap suckers that leave the foliage looking yellow, drained of goodness and washed out.
You may even notice fine, almost web-like dust on the under sides of the leaves. They LOVE our indoor plants.
Leaf borers or leaf miners leave wiggly white lines or rather tracks throughout the membranes of the leaves. (pictured above)
Also sucking insects, Aphids, mealy bugs, scale, and thrips are all a little larger and visible to the eye. These types of insects often leave their secretions behind called 'Honeydew'. A sweet, sugary substance that goes onto to become black and mouldy, not before the ants come marching in droves!
Caterpillars, snails, slugs and grasshoppers are all munchers and crunchers, they leave obvious holes in the foliage if they leave anything at all!
Larger pests like birds, rats, rabbits and possums will devour small, tender delectable little seedlings and leave not much more than maybe a stem as evidence that they existed. Possums LOVE our roses and fruit trees. I've seen young fruit trees, and new seasons growth on roses stripped of everything bar the stems of the leaves.
Rabbits, Kangaroos and rural livestock are renowned for 'ringbarking' young trees (removing the outer layer of the trunk)-but then so can a whipper snipper (ask my passionfruit vine what happened the day I took home a new Makita line trimmer🤭)
Larger animals if given the opportunity to get into the veggie patch, may leave your plants crushed, broken and perhaps even pulled from the ground in the way that they graze.
Above left- Grasshopper. Centre- Aphids. Right- Earwig.
Below left- Mealy bugs. Centre- Scale. Right- White fly.
Evidence of disease
These next two scenarios are kind of closely connected. Often, disease takes hold in a plant as a result of the same inconsistencies that lead to a diagnosis of a disorder.
Avoiding situations that lead to disorders can often prevent them being susceptible to disease.
Three of the most commonly seen diseases in our home gardens are Black Spot, Powdery Mildew and Rust, all fungal diseases manageable with fungicides.
Copper oxychloride and Lime sulphur are two of the most common fungicides on the market along-side more natural friendly alternatives like milk or bicarb soda.
Black spot will be all too familiar for anyone who has ever grown roses. Almost always seen on roses towards the later part of the season when they're tired and running out of puff, particularly where there is over crowding of foliage, creating a lack or air circulation. A lack of air circulation combined with the right degree of humidity (moisture in the air) creates the perfect breeding ground for not only black spot, but for most fungal diseases.
Early stages will look like perfect round black spots randomly spread over the leaves. As it progresses those leaves lose their green pigmentation turning yellow, then finally falling from the plant.
Powdery Mildew begins will small powdery white looking blemishes on the leaves and stems. It progresses to cover the entire leaf surface with the foliage eventually shrivelling and dying. Commonly see on Zucchini's, pumpkins, melons and cucumbers. Hydrangeas and grape vines, edible and ornamental are also highly susceptible.
Rust is something our farmers are constantly on the lookout for in their wheat and barley crops, it can be a problematic issue for them most seasons.
Easily identifiable by the presence of tiny, raised almost fuzzy looking orange, red or brown spots. Keep an eye out for it on veggies like tomatoes, peas and beans, and amongst flowering annuals, calendulas, snapdragons, gerberas, hollyhocks and geraniums will be the most susceptible.
Evidence of disorders
Diagnosing a disorder can be a lot trickier than an obvious pest infestation or a disease, as a lot more factors come into play.
A disorder can be summed up as any situation where a plant doesn't look as it should or isn't performing as it should be relating to water, nutrition, environment or climatic factors.
Process of elimination- if there's no evidence of pests, or disease, then it has to be a disorder. (the fun part is establishing which one it is!)
Nutritional deficiencies or toxicities for want of a better way to describe it, plants need the right proportions of nutrients from all the 'food groups' just like us. Think of the healthy food pyramid, although their food pyramid would look a little different from ours, but the concept is the same. Too much or not enough of one thing will see them screaming out to us with clues ranging from a lack of pigmentation, to curling of leaves, too much pigmentation and crispy burned leaf margins amongst others.
HINT** Often a customer will approach me asking for Iron to take home and treat their yellow plant. In some instances, they'll be 'bang on the money' that it is an Iron deficiency, but if you're not 100% certain, resist the temptation to treat is as such, because you could potentially cause further issues poisoning your plant with something it never in fact needed. Always err on the side of caution, do a little homework first.
Hydration A plant can look wilted and droopy because it's thirsty, on the other hand it can look droopy if it's lacking in oxygen/drowning too.
HINT**I mentioned earlier that disorders can sometimes lead to disease? Root rot in indoor plants is a disease that unfortunately occurs as a direct result of too much water/wrong potting medium.
What is your watering rescheme? How much water does this particular plant actually need? Has your soil become hydrophobic not allowing it to take in and hold water, or on the other hand, is it holding too much water drowning it, should it be planted in a more, free draining medium? All questions taken into consideration if a hydration disorder is suspected.
Burned shrivelled foliage can also be a result of inadequate water.
Climatic conditions, soil & light can most definitely come into play when assessing why a plant is unwell or is failing to thrive.
Knowing the climate zone and habitat a plant originates from can tell us a lot more about its preferences, and the environment it will most likely thrive in.
A plant that originates from a hot, arid climate, quite likely has the ability to store water in its roots or fleshy leaves (think cacti and succulents), some have small fine needle like foliage to minimise the opportunity to burn in the sun and lessen its need for water. (think of native coastal rosemary or saltbush).
Plants like these will most likely fail to thrive and struggle in a heavy rich soil in full shade, just as ferns, fuchsias and hydrangeas will quite likely burn and shrivel in sandy soil, in the full hot afternoon sun.
Being able to look at a plant and establish what is wrong with it, is not something you can learn overnight. It's knowing what to look for and where. Being able to look at a plant's characteristics, for clues to its origins to know what its preferences are. It's a whole jigsaw puzzle that comes together to build a picture.
It's a skill that has taken me personally, years of study along-side working with plants every day to become confident with, and I'm still learning something new every day. We never stop learning.
I hope there are some useful clues here that might help you to work out why your plant may be sick.
And if all else fails, please reach out, send me a message and we can work it out together. Or our lovely Limestone Coast locals will know where to find me.
Keep praying for rain, it's bound to come soon.
Happy gardening 😘🪴🌸
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