Common plant problems… and how to avoid them

My seedlings are floppy… and covered in mould!
Ever heard of damping off? It sounds like yet another gardening technique, but this is a problem that affects young seedlings. It can take hold before seedlings even emerge, causing patchy germination – or no germination at all. But it’s probably more easily identified in seedlings which collapse and sometimes become covered in white mould.
Damping off is caused by fungi and other fungi-like organisms that thrive in pots and trays which are overwatered, poorly ventilated and overcrowded. It can wreak havoc on your fresh sowings at any time of the year, but it’s most common in spring when light levels and temperatures are lower, and under glass, where there’s less air circulation. Try sowing seed thinly, don’t overwater and keep the area well-ventilated. Like all fungi, damping off organisms love cramped, humid conditions – so don’t give it to them! Also, make sure any pots and trays you use haven’t been affected by damping off before, and wash and disinfect them before use.

There are small brown spots on the leaves of my plant!
On the surface level, this is can be due to too much or too little of something – sometimes fertiliser but, most commonly, water. Not watering enough means your plants aren’t getting the vital life element they need to photosynthesise, but too much at the roots can inhibit the oxygen needed for this process to take place.
And beyond that, waterlogged plants bring a new issue altogether: a place for disease to thrive. When leaves become dotted with brown spots all over, this can signal that leaf spot diseases – bacterial, fungal or viral – are attacking the plant.
If it’s pustule-like spots you’re looking at, rust could be to blame. A common fungal disease, cases range from mild to severe. Rarely, the pustules will spread to the stems, flowers and fruits. Rust doesn’t always cause the plant harm, but if the infection worsens, it can reduce the plant’s vigour – in some cases, halting growth altogether. If only a few leaves are infected, remove and dispose of (but don’t compost) them. Rusts which infect edibles don’t tend to respond to fungicides, so it’s important to try and protect against infection in the first place. The disease is spread through spores, so ensure there is good circulation around your crops. You should make sure that your soil is able to drain well to prevent your crops from sitting in water. Also, try to water the base of the plant instead of soaking the whole crop – moisture is a friend of fungal disease. Sometimes, even these measures aren’t enough to cover all risks – and pests can strike at any time, causing similar browning effects.

Why are the leaves of my plants yellowing?
Yellowing of the leaves of a plant – or chlorosis – can be traced back to a number of reasons. Unfortunately, the wishy-washy subject of watering is one of them – too much or too little can hinder a plant’s growth and, especially in the case of drought conditions, can lead to leaf loss. If your soil easily becomes waterlogged or is compact, root rot might occur and worsen the problem, so consider implementing drainage measures or loosening the soil prior to planting.
Often, though, chlorosis is down to a lack of nutrients – or too many of the wrong ones. Accompanied by slow growth and legginess, yellowing leaves can be a sign of nitrogen deficiency, for example. The location of the yellowing can hint at what deficiency is causing the problem – for example, potassium deficiency might reveal itself with yellowing towards the leaf edges, while yellowing between leaf veins which begins on the youngest leaves could signify a lack of iron. A mottled pattern, on the other hand, could be a sign of a mosaic virus, especially when accompanied by stunted growth, and affected plants should be destroyed to prevent transmission to other crops.
Pests might even be to blame, especially those which attack the foliage – aphids, red spider mites and whiteflies – and the roots, like root flies and vine weevils. These pests can usually be identified around the plant and dealt with accordingly.
While using fertilisers is useful in the short- term, having good, nourishing soil is key – incorporating compost or well-rotted manure into the soil will ensure a slower and therefore longer-lasting release of nutrients into the soil.

My crops have developed a tough flowering stalk!
Bolting is a term which describes crops running to seed too early, before they can be harvested. It’s a survival mechanism – when unpredictable conditions strike, usually like sudden changes in the weather or day length, the plants mature quickly and begin to produce seed for the next generation. In essence, any conditions that put the plant under stress can trigger bolting.
There are several measures you can take before planting to ensure there is less chance of your crops bolting. If you’re sowing direct outdoors, try to wait until fluctuations in temperature are less likely. This is especially helpful for edibles that are sensitive to the cold. If you do sow during unpredictable weather seasons, cover your sowings with cloches or horticultural fleece to protect them from harsh changes in temperature or weather conditions. Better yet, sow seed indoors and plant them out when temperatures are warmer, making sure to harden them off first. It’s also a good idea to look out for bolt-resistant varieties if your area is prone to unpredictable weather – there are lots of choices available for veg such as onions, beetroot and more. For other crops, the heat isn’t favourable – like radishes and spinach – so consider shading these edibles during hot spells to reduce the likelihood of them running to seed.

Why are there dark blotches on my tomatoes?
This symptom is most likely that of blossom end rot, a common culprit in the case of tomatoes, peppers, aubergines, melons, cucumbers and squashes. It happens when the fruits don’t receive enough calcium, and it isn’t a disease – it’s all down to the plant’s needs and what they don’t get enough of.
Blossom end rot begins as a dark bruise which progresses into a sunken, circular black patch on the blossom end of the fruit – the end that is furthest away from the plant. The patch gets deeper as it increases in size, until fruits become flat on one side – the side that’s lacking in calcium.
A lack of calcium in the fruits does not mean there is a deficiency in the soil – usually, it’s down to an inadequate flow of water through the plant. Due to the distance of the fruits from the roots, the plant needs enough water to get the calcium to them. Plus, hungry leaves might snatch it up before it gets there.
Fertilisers can also be problematic, especially when used on dry soil – they can compete with water and prevent total hydration of the plant, so try to use them on wet soils when the plant has surpassed its early fruiting stages. Humidity can also be a problem, so make sure your plants are kept in a ventilated space. Anything that limits or inhibits the supply of water that is taken up by the plant roots can increase the risk of blossom end rot.
Several factors can worsen this problem. Container-grown plants are more prone to an irregular water supply, so try to choose larger containers and keep the soil moist at all times – never let it dry out. Mulching is a great way to conserve moisture around the roots.
The good news is that by correcting this problem early on, the other fruits will have the chance to develop normally. Plenty of harvests left to enjoy!

There’s a white coating on the leaves of my plant…
Powdery mildews are common fungal diseases which affect a wide range of edible crops. The fungus is visible as a dusty white powder which covers the surfaces of foliage, flowers, and sometimes fruits. Dispose of fallen infected leaves in the autumn and remove any infected shoots. Ensure there is good air flow around vulnerable plants, which should not be planted too close together – this disease, like many others of the fungal kind, love humid conditions, so ensuring a good level of ventilation is key. Planting away from walls is therefore another good tactic.
Downy mildew, on the other hand, presents itself as leaf spotting, usually white or yellow and sometimes progressing to a grey or purple mould. If the infection is severe, the leaves can eventually turn yellow or brown and drop, and the plant’s vigour and growth can be severely stunted. In these more serious cases, entire plants should be destroyed to prevent the spread of the fungus to other crops. However, leaves can often be picked off singularly when infection is spotted. As with powdery mildews, ensure humidity levels are kept at bay and air circulation is a priority – keep the leaves as free from moisture as possible, too, and practice crop rotation.

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