Depending on where you live in the UK, the weather can be very different from the summer months to the winter. Plants generally prefer to have a constant environment in order to grow optimally. Keeping this temperature and humidity as stable as possible for most crops will give you the best results overall.
Faster growth, and bigger yield are the ultimate goals with hydroponics, which begin with giving the plant exactly what it needs.
Although most grow rooms are indoors, the outside weather can have a huge impact on your grow room's temperature, and humidity levels. The lights in your grow room produce heat, the plants and hydroponics system will release water and drive up the humidity, and the ambient are outside can either add to this, ro reduce it. The goal is to find a balance in the grow room to keep the constant environment. Too hot and your plants will close their pores to protect themselves from losing too much water through evaporation, too cold and they will stop growing and try use their stored energy sources instead to survive. Neither option is optimal for your plants growth.
Humidity can also have a big impact on your plants growth. High humidity can quickly lead to mould or bacterial infection, and too dry and your plants may begin to dry out and die. Keeping the stable middle ground is the goal no matter what the conditions outside are.
All the air going into the grow room comes from outside. If the air is dry, it will reduce the humidity levels in the room. This may work to your advantage in a grow room that tends to be too humid, but can make matters worse in already dry grow environment. Depending on the seasons, these conditions will change, which will require you as the gardener to take be adaptable, and make changes to your grow environment to ensure these levels remain in the correct range.
In the winter, temperatures can dip as low as -10 C, but generally sit somewhere around the 0C mark. They tend to be very wet and rainy as well, which means the humidity in your grow room will increase substantially.
Gardening in the winter often means adding some heat to the grow room, and reducing the humidity. Decreasing your extraction fan speed can increase the heat, but will also increase humidity. You can avoid this by adding a dehumidifier to the room and turning the ventilation down, or keeping the ventilation high, but adding some heat from a portable heater.
As we shift into spring, temperatures will begin to heat up, but the humidity levels will generally remain about the same. Having a heater on hand will still be required from time to time when the temperature dips, but the main consideration will be keeping that humidity down. The easiest way to do this is with a dehumidifier, but can also be accomplished by increasing your exhaust fans. Make sure those circulation fans are working well though too because stagnant, humid air is never a good thing in a grow room. That's an invitation for fungal, or bacterial infection.
The summer temperatures in the UK are much higher, somewhere around 20C. The weather can still be fairly rainy, but is more erratic and less constant. This will mean that your focus on humidity levels in your grow room will change from day to day. Keeping a dehumidifier is a good idea for all seasons in the UK, and finding one with an automatic humidity sensor will make your life a whole lot easier.
These dehumidifiers will sense the ambient air humidity, and decide when to turn themselves on and reduce the humidity levels, like after a spell of summer showers, and when to turn off in order to avoid drying your plants out during a dry period.
If you don’t have an automatic dehumidifier don’t worry, you can make simple changes in your ventilation fan speed from day-to-day to account for this. Keep an eye on your humidity sensor, and don't be afraid to crank up the exhaust fans when it starts to get over the 50-60% reading.
As we head back towards winter, this is when the temperature and humidity levels will change the most. It is not uncommon for temperatures to be above 20C and 30% humidity in the morning, only to turn into 7C and 60% humidity in the afternoon. This is the time of year that the indoor hydroponic gardeners need to pay the most attention to the parameters in your grow room, and make any changes accordingly.
Luckily, frost is not an issue in indoor gardens, and overheating is uncommon as well, the house or building your garden is in will serve as a buffer from either of these two extremes, and it is uncommon for a hydroponic gardener to lose his crop due to outdoor conditions in the environment. Most of the problems will come from long term environmental changes such as higher ambient humidity, or insufficient heating or cooling that will build up in the grow room. Paying attention to your grow room environment with the use of a temperature and humidity gauge will ensure you stay well within the optimal range for each no matter what season you're in.