Protect Your Crop in Autumn

As the nights draw in and the days get shorter, autumn brings with it a fresh set of challenges for indoor growers. Outside, temperatures are dropping, rainfall is increasing, and humidity levels are on the rise. And while your grow room might seem like a controlled environment, those external seasonal shifts can have a significant impact indoors too. From increased risk of mould and mildew to slower plant metabolism and nutrient uptake, autumn conditions require careful attention — and often, a few key adjustments — to keep your plants thriving.

With cooler, wetter weather outdoors, spores and pathogens become more prevalent in the air. These can easily make their way into your grow room on clothing, tools, or even through ventilation systems. Once inside, higher humidity and fluctuating temperatures provide ideal conditions for problems like powdery mildew, botrytis (bud rot), and other fungal issues to take hold.

The best defence is a combination of environmental control and good hygiene, as well as ensuring that you avoid bringing contaminants in from the outside. More importantly, manage your humidity carefully. High humidity

combined with stagnant air creates the perfect breeding ground for moulds.

Proper air movement is another key defence. Oscillating fans and effective circulation prevent pockets of still, moist air from forming around dense plant canopies where pathogens thrive.

As temperatures outside fall, so too will the temperature inside your grow space — unless you actively compensate for it. This is especially true for grow rooms in garages, lofts, or outbuildings, where insulation is often limited. Cooler temperatures slow down the rate of photosynthesis, reduce root activity, and hinder substrate dryback. That can lead to a cascade of problems, from nutrient deficiencies to stunted growth and reduced yields.

To maintain optimal growth, aim to keep daytime temperatures stable and night-time drops minimal. Supplemental heating is often necessary through the autumn and winter months, and the cost is far outweighed by the benefits in plant performance.

Autumn humidity swings can be difficult to manage. On one hand, cooler temperatures mean the air holds less moisture, which can sometimes dry the environment too much during lights-on. On the other, increased rainfall and damp weather can push humidity levels too high during lights-off, especially as transpiration slows down.

Automated fan controllers that adjust extraction based on humidity and temperature are an excellent way to stabilise conditions without constant manual intervention. These ensure your environment stays within ideal parameters, even as outdoor conditions change throughout the day.

Lower temperatures and higher humidity also slow down substrate dryback — the rate at which growing media dries between irrigations. This can lead to oxygen starvation in the root zone, a build-up of salts, and even root disease if not addressed.

Consider adjusting your irrigation schedule and improving heat or airflow around the root zone to encourage a healthy wet-dry cycle. Tube heaters are a great way to gently heat the areas around your pots - being slim and low wattage - with many growers using multiple heaters throughout the growing footprint to assist dryback.

Switching your pots over from plastic to fabric will also help the substrate to dryback faster and assist with oxygen replenishment to the rootzone, alongside other benefits.

One effective layer of defence against mould and mildew is the use of preventative foliar sprays. These sprays coat leaves and buds with a protective barrier that reduces the likelihood of fungal spores taking hold. They are particularly useful during the damp, cooler conditions of autumn, when high humidity and poor airflow increase the risk of disease. Used as part of a broader strategy — including controlled humidity, good air circulation, and clean growing practices — foliar sprays can help keep your plants healthy and free from fungal infections.

The transition into autumn doesn’t have to spell trouble for your grow. By anticipating these seasonal challenges and adapting your setup accordingly, you can keep your plants in peak condition right through to harvest. Focus on maintaining stable temperatures, managing humidity proactively, and keeping air moving — and don’t underestimate the importance of reliable environmental control equipment.

Autumn brings new dynamics to your indoor garden. With colder air, increased moisture, and a rise in pathogen pressure, the margin for error becomes smaller — but so does the gap between an average harvest and an exceptional one. A well-prepared grow room, equipped with the right tools to handle seasonal changes, not only safeguards your crop but sets the stage for even better growth. Stay ahead of the conditions, and your plants will reward you all season long.