To prevent mould on your canvas awnings, the most important thing is to ensure you dry it out well after each use.
If you use water and diluted bleach solution (do not use vinegar - the acidity will damage your awning), you can't really go wrong with your cleaning solution. This is one of a few things you can try on your awning. If it is mould, elbow grease to clean surface as much of your awnings as you can. Ensure you are wearing rubber gloves and old clothes and lay down some plastic sheets.
Mix a solution of 1 part cleaning fluid to 10 parts water in a bucket or bowl before you need to clean. Start with a small patch on your fabric.
Add the cleaning solution to a treatment spray bottle and thoroughly wet the mouldy areas of the fabric of your awning to soak and then brush with a broom. Then start cleaning. You can keep all your cleaning products safe in an outdoor area for easy access.
Soak for 30 minutes, wipe down the awning's fabric with a cleaning cloth or soft brush and allow the canvas awning to dry completely in the sun.
You can add organic materials like tea tree oil to your cleaning solution if you want - this is an effective anti-fungal cleaning agent that has been used traditionally in Australia. The same goes for eucalyptus oil - it's great when added to tea tree oil as well! Just ensure that whatever essential oils you use are not phototoxic, ie: do not expose them to sunlight after using otherwise you risk serious skin damage and use a soft brush for cleaning the fabric.
Most of the time, this process is sufficient for cleaning, and your old canvas awnings will look as good as new. Of course, it can't fix small tears or massive rips in the fabric so if you have those issues, you'll need to stitch them up with some tent repair tape first before using the cleaning solution.
You can also try using a specialised mould removal product on your canvas awnings but be careful with strong chemicals for cleaning. A lot of these products require full ventilation and may not be suitable for use in enclosed spaces without proper safety gear also make sure it doesn't soak for too long (just like you'd wear when spray painting).Both are great at cleaning mould on outdoor furniture as well, however, they are both completely different things for mould. Vinegar is an acid but bleach is an oxidising agent which actually turns the mould spores into inert crystals that are then easily washed away with a clean water hose from the fabric or canvas. Vinegar will also disinfect the fabric or canvas to some degree. Its mild acidic preservative qualities won't kill every micro-organism in the mould from the canvas though so if there have been any dead skin cells in your mouldy canvas awnings, you may need something stronger for heavy-duty cleaning. This goes for any strong odour left behind by bleach. Nothing can beat throwing your canvas in the washing machine on a hot cycle with some enzymatic detergent for really killing lingering smells and a good wash.
To prevent mould on your canvas awnings, the most important thing is to ensure you dry it out well after each use. Remember that if it's cold outside, drying will take significantly longer than when the sun is beating down. If you're in warmer climes, try using some UV-resistant fabric spray prior to storage - this will definitely help protect your canvas awnings from mould. If you live somewhere really wet (ie: tropical climates), the general rule is to be sure to wipe it down with distilled vinegar or bleach solution before leaving it up for too long as mould can easily grow between waterlogged canvas fabrics and metal poles. Some other tips are to keep your whole awning closed up when not in use so moisture doesn't get trapped inside the fabrics causing mould during humid weather, also keep bird poop and dirt away.
Algae can be troublesome on your canvas awning. You'll need to get the algae off with a wire brush and then scrub with some white vinegar cleaner mixed in water from a hose and let it stand for about an hour before scrubbing with mild soap and warm water to rinse. Pay special attention that like mould, algae is likely to grow unless washed regularly and keep your canvas dry when not in use. So you will need to clean it properly. The best way to protect your canvas awnings from algae build-up is to store them in a well-ventilated area when possible this helps with the mould problem and keeps dirt away. Avoid the temptation to keep the awning in storage over winter, even if you live somewhere that doesn't get too much rain or snow. Algae thrive in moist air, so make sure you wipe the awning down in the springtime to remove any excess levels that cause mould before they develop into unsightly black dust bunnies. It's important to note that even if your awning doesn't have an algae problem, it still needs regular cleaning with mild cleansers like white vinegar or bleach. Keep an outdoor cleaner handy for your awning. This is because no matter what colour or type of awning you buy, it will eventually absorb water cause mould, and when this occurs over time, algae spores are able to grow. The only way to really keep water from awnings at bay is by scrubbing regularly with gentle solutions (and always ensure your awning is completely dry before packing away each season).
The most common type of mould that grows on a canvas awning is black mildew growth apart from loose dirt. This is what you get when the awning becomes waterlogged and begins to rot, resulting in dark-coloured dust bunnies (algae spores) or patches of black slime (mould).
Mould comes in all colours, including yellow, pink, orange and green. Some can be very difficult to see on white awnings but will appear as smudges. Visible black, white and green mildew stains usually mean the awning has been exposed to excessive amounts of moisture and is rotting. Pink, orange and yellow staining often occur when the awning hasn't been thoroughly cleaned after exposure to dye or oil-based paints.
Mould can sometimes be difficult to spot on the awning because it grows in little white patches that look like salt grains (particularly on dark fabric) and while bleach helps for lighter coloured strains, there's no real way of getting rid of each and every type if you retract your awning while wet.The best way to remove mildew or clean mildew from your canvas awning is by using an enzyme-based detergent with your cleaning equipment, once the weather starts to warm up with a soft bristle brush. This will ensure algae spores don't have anything moist to feed off on the canvas awning and can't develop into unsightly patches of black slime. Vinegar or bleach solutions are good for cleaning mould, but won't kill algae spores so you'll need to remember how important it is to dry your tent out well after each use.
White powdery marks are usually caused by mildew on canvas that's built up over several years mostly on outdoor awnings. It is almost certainly green or pink algae that gradually become worse. To make it easy to remove the powder, add some water to rinse from a hose and vinegar (1:2) in a spray bottle and spritz the affected area with mildew on the awning once every few hours for up to two days. After that, use a wire brush with stiff bristles to remove any remaining traces of mildew from the awning and the canvas or a soft broom and then scrub with warm soapy water from a mild soap mixed in a bucket or hose (add 1 teaspoon of liquid soap and 2 cups of white or cider vinegar per 5 litres of lukewarm water, not cold water) and then air dry. Avoid using bleach to clean mildew as this can damage the awnings colour fastness and leave a white soap residue stain. This process also creates water resistance in the canvas.
If this isn't possible, then ensure your awning is completely dry before putting it into storage - and don't forget that canvas tents left in direct sunlight during summer can also get hot enough for water droplets to gather inside the awning.