It’s common knowledge that mould loves damp, humid conditions in our homes, but did you know that it can also thrive outside? Our gardens are hotbeds for bacteria and some moulds are most prevalent during spring and summer, thanks to the increase in hot and humid weather.

Sadly, this poses a serious threat to garden plants and wildlife, which is why we've created a guide to common outdoor mould varieties and how to get rid of them. Click or scroll on to gain the know-how to make your garden a safer place for everyone...

Mould is a type of fungi that grows best in damp and poorly ventilated places, including outside. "Mould may look like fuzz, or discolouration or a stain on material like wood," ACT Health explains. "Spores are the microscopic ‘seeds’ which fungi, including moulds, release into the environment. They are sufficiently small that they can be suspended in air and widely distributed." 

Exposure to some mould varieties can trigger allergic reactions and even respiratory issues. “People with pre-existing medical conditions such as impaired immunity, allergies, severe asthma, emphysema or allergic lung diseases may be more susceptible to mould.”

So, what causes mould? Mould requires moisture to survive, which is why it can often be found indoors in bathrooms. However, it can thrive in almost any environment if the conditions are right.

AXA suggests that “humidity is one of the most common reasons mould occurs”, as well as condensation, which is “usually caused when warm air collides with cold surfaces. The moisture in the air cannot escape, resulting in mould.” Other causes can be rising damp and poor airflow.

You might be wondering, what's so bad about having a bit of mould in the garden? Well, mould has the power to drain nutrients from plants, stilting their growth and leading to diseases. Some moulds can cause stems to rot, eventually killing the plant.

But it isn't just your flowers and vegetables that will suffer...

According to garden centre Polhill, mould is also bad news for UK birds. "They are especially vulnerable to the harmful effects of mould due to their sensitive respiratory systems," explains Polhill's director, Josh Novell. "Exposure to mould spores can cause respiratory problems, such as coughing, wheezing and difficulty breathing. In severe cases, it can even lead to pneumonia or other respiratory infections."

Most UK bird species can pick up toxins from mould through infected feed, nesting boxes or general contact. So, preventing the growth of mould requires proper garden maintenance and hygiene. 

Now, let's take a look at the most common types of mould found in the garden and what causes them...

Slime moulds affect lawns throughout the year, but are most common in late summer and autumn alongside humid conditions. According to the Royal Horticultural Society, "The spore-producing structures of slime moulds can appear on lawns quite suddenly, sometimes overnight."

The most common slime moulds are Physarum cinereum, Mucilago crustacea (pictured) and Fuligo septica. Luckily, these are easy to get rid of, the RHS says: "No control is usually required" and you can simply spray the patches of mould with your hose to disperse them. They will clear up in drier weather.

Another mould that affects lawns is snow mould – also known as Fusarium patch – which is common after snow thaw (hence its name). You might first notice it as small patches of yellowish, dying grass that later turn brown.

Although it's less common in summer, wetter weather mixed with heat means it can appear at any time of the year. Turf constantly damp or in the shade is more likely to develop snow mould. Other exacerbating factors include poor drainage or clay soil as the lawn cannot fully dry out.

As well as trimming back large bushes, shrubs or trees that keep your lawn in the shade or block airflow, it's also a good idea to scarify your lawn, with a rake or lawnmower. Scarifying is 'scratching' the grass to remove any build-up of dense patches that can't 'breathe'. You can also aerate your lawn with a garden fork or specialist tool.

Moving from the lawn to your plants and flowers, the three most common garden moulds to watch out for are Cladosporium, Alternaria and Aspergillus.

Cladosporium appears in clusters of black, yellow or green spots. “The spots spread quickly when not cleaned away. Cladosporium often forms where moisture is present,” Medical News Today explains. Cladosporium includes more than 40 individual species of fungus and, outside, can be found on decaying trees, dead plants and tree trunks.

Alternaria, which can cause damage to crops, such as cereal grains, fruits and vegetables, will also attack trees and plants. The mould “is often responsible for leaf spots and degenerative diseases on trees and bushes”, Mold Advisor warns. The mould lingers in the air on dry, windy days and when airborne will seek out "a warm and humid place to start a colony".

Alternaria is also an allergy-causing fungus. In fact, Alternaria sensitivity can lead to severe and potentially fatal asthma. “Studies have shown that up to 70% of mould-allergic patients have skin test reactivity to Alternaria,” an expert from Mold & Bacteria Consulting Laboratories says.

Another highly common mould is Aspergillus, which is "often found growing on dead leaves, stored grain, compost piles or in other decaying vegetation", Penn Medicine explains.

The fungus is black on the surface and usually white-ish or yellow underneath, however, there are around 180 species. "For people who have weakened immune systems, breathing in Aspergillus spores can cause an infection in the lungs or sinuses, which can spread to other parts of the body," the Centers for Disease Control and Prevention warns. Luckily, there are steps you can take to limit garden mould. Let's find out more...

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According to Medical News Today, birds and their droppings can carry over 60 diseases, so regular cleaning of birdhouses is not only beneficial for attracting birds, but for maintaining their health and your garden's. Bird houses should be cleaned at the beginning and end of every breeding season. In the UK, nesting season begins in February and can extend until roughly August. Great care should be taken to avoid disturbing nesting birds. 

Old bedding and droppings attract garden pests and provide a breeding ground for fungi. "Bacteria, mites, mould and other pathogens can thrive in unclean birdhouses, leading to various health issues for the birds. By regularly cleaning and disinfecting birdhouses, you help prevent the spread of these harmful agents," HummingbirdsPlus suggests.

In much the same way as birdhouses, bird baths and feeders also need to be cleaned regularly to stop the spreading of mould and diseases. In fact, Conserving Carolina suggests that bird baths and feeders should be cleaned even more regularly. "These structures tend to be shared by more birds than houses and therefore have a higher risk of disease transmission," they explain. "During times of heavy use, such as breeding season, these should be cleaned every two weeks or so." 

Rinse and scrub the bath with one part vinegar to nine parts water. Refill with fresh water every other day. Feeders can be cleaned in the same way, or placed in a dishwasher on a hot setting.

Any bird feed located outside will get wet during rainy days, even through spring and summer. "If this happens, it can begin to form mould," Josh Novell explains.

To prevent this, you can relocate your feeders to a sheltered area, where they're less likely to be impacted by wet weather. If your bird feed becomes wet, it's best to throw it away, clean and dry the feeder and refill it with dry seeds.

A great alternative is buying or making a bird feeder with a protective rain guard built in. While you can get some feeders with little wooden roofs, others will come with a special dome that acts as an umbrella, allowing rainwater to fall right off.

"Having these will protect the seeds and the feeder from getting damp, which might stop mould growth," Josh suggests. Plus, we think they look far cuter in the shape of houses.

This one is less obvious, but just as important. If your gardening tools come into contact with mould and you forgo cleaning them, you could inadvertently carry the mould spores from one area of the garden to another.

Polhill recommends cleaning and disinfecting your gardening tools regularly, using soap and hot water. If you spot mould and are using any tools to tackle it, then be sure to clean them before moving on to another part of the garden. You should also store them where they will be dry. 

We all know that mould thrives in damp, moist environments, which makes dead or decaying plant material, fallen leaves and other garden waste an absolute haven for mould spores.

"Moulds thrive on organic matter and cleaning up this material can help reduce their food source and stop birds from getting infected if they come into contact with it," explains Josh Novell. So, don't leave garden debris lying around.

In the same vein, it's essentially that all garden waste is disposed of properly. "Composting can be a good way to recycle garden waste, but ensure that the compost pile is well-aerated and properly managed to prevent mould growth," Josh suggests.

"If you suspect mould-infested plant material, it's best to discard it in a way that won't reintroduce it to your garden." The best way to do so is by taking your garden waste to your local tip or recycling centre.

Since all moulds thrive in damp conditions, it’s essential that your garden isn’t waterlogged. “Be mindful when watering your garden during drier spells,” Josh Novell suggests. “Avoid overwatering, which can lead to waterlogged soil and encourage mould growth.”

If you often see water pooling in your garden, then you may need to improve your drainage. This will prevent water from pooling around plant roots. “Simply amending the soil with organic matter like straw and grass clippings can improve drainage and will stop mould from thriving.” 

If the problem is severe, then you might need to invest in a garden soakaway – which is essentially a big hole dug in the ground that collects excess rainwater and allows it to drain away gradually.

It might sound odd, but it's essential to maintain good air circulation in the garden. Proper air circulation will help "prevent the development and spread of various plant diseases caused by fungi, bacteria and viruses", Gardening.Gov.Capital explains.

Proper airflow will reduce humidity, improve pollination and prevent fungal spores from dispersing. The best way to achieve adequate airflow is to space plants far enough apart to avoid overcrowding. Regular pruning will help thin out dense areas.

Using too much mulch is one of those bad home habits you need to stop immediately. While mulch can help retain the moisture in your soil and suppress the growth of weeds, it can also create a favourable environment for moulds if applied too thickly, or if it becomes compacted. 

Overdoing it can cause moisture retention, leading to plant disease and decay. Polhill suggests using mulch sparingly and regularly fluffing it to prevent moisture build-up. A one- to two-inch layer of fine mulch or three to four inches of a coarser material should be sufficient.

No one likes weeds. These undesirable plants are difficult to control, look unsightly and always crop up where you least want them. But there's another reason why you should be regularly tackling the weeds in your garden.

"Weeds can trap moisture and create shaded, humid areas in your garden during warmer spells, making it more conducive to mould growth," Josh Novell explains. "Regularly remove weeds to reduce these conditions."

The last thing you want is for mould to find its way into your new bag of potting soil. If it does and you don't notice, you could quickly find yourself with a garden full of harmful spores. "If you have bags of potting soil or compost, store them in a dry, covered area to prevent moisture infiltration and mould growth," Josh Novell says.

Simple Grow suggests keeping potting soil in an outdoor shed or garage since these areas are cool and have enough airflow to keep the containers from becoming too damp. "It should also be stored in an air-tight container with no pests or insects so that its quality is not compromised."

The experts at Polhill advise that, as a last resort, you could consider using fungicides, which are specifically formulated for garden use. These potent pesticides will prevent the growth of fungi and their spores, stopping them from spreading.

"However, it's generally best to rely on cultural and preventive measures before resorting to chemical treatments," Josh Novell says. 

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