One of the biggest advantages of having a greenhouse is that you can extend growing seasons, getting an early start on spring and summer and even growing certain vegetables all year round. Our growing guide gives you a good insight into what should be planted when, but before you even start planning your growing schedule, it is important that you load up on the vital seed starting supplies you’ll need for a successful yield. At a minimum, you should invest in:
We also recommend you invest in heat sources to help propagate seeds at the beginning of the season when temperatures are cooler. A propagation heating mat is an inexpensive and easy way to heat seed flats and encourage growth, but there are other methods such as heat cables buried in seed benches.
During late Spring and Summer, any Swallow or Elite greenhouse should be getting enough natural light for the plants, but if you want to grow in late Autumn and Winter, a supplementary lighting system is a must-have if you want healthy, strong plants.
High output fluorescent lamp strips and LED grow lights are amongst the most popular lighting products because, unlike some other lighting systems they output full spectrum light, are very energy efficient and can cover a larger area.
However, if you’re in a small and cheaper greenhouse, or are growing a smaller crop, a normal fluorescent strip hung 3-7 inches above the plants will often suffice.
Heating a greenhouse in the cooler months can be quite the learning experience in and of itself! For those new to greenhouse growing we recommend using electric heaters as they are easier to install, more economical and have a wider range of applications. A small 120-volt heater will usually heat a small greenhouse just fine, although larger greenhouses will need a 240+ volt heater, controlled by a reliable, waterproof thermostat.
Gas heaters work just as well, but tend to be less economical and come with the added nuisance of sorting out proper ventilation, with both a constant supply of fresh air for combustion and a means of fume exhaustion.
For the eco-minded out there, less energy intensive forms of heating include setting up ventilation systems which use unneeded warm air from your home. Some growers with small greenhouses also use items like large rocks and other heat-absorbent materials which absorb heat during sunlight hours and slowly release it throughout the night. Even with supplementary heating sources, these methods are a good way of keeping the temperature inside the greenhouse more consistent throughout the course of a day.
Even with the UK’s milder climate, during the height of summer it can be hard to maintain a consistent temperature in a greenhouse. Because they are specifically designed to maintain and trap heat, cooling down a greenhouse that has become too hot is far harder than heating a greenhouse that is too cool.
Therefore consistently and regularly measuring the temperature inside the greenhouse or potting shed during the hotter months is hugely important. Measuring temperatures regularly can mean the difference between being able to regulate temperature by simply opening the greenhouse door and having to use positive cooling. If your greenhouse does regularly overheat, we recommend using evaporative air coolers, which maintain humidity.
Seasonality plays a huge role in ventilating any size greenhouse. During the summer, convection currents created by the natural heat is more than enough to maintain good circulation. By keeping both the wall vents and the roof vents open during summer, cool air will be pulled in through the walls while hot air will escape through the roof, drawing in a constant supply of fresh air.
During winter, however, maintain air circulation and preventing the growth of mold can be more difficult. Making sure that the soil is not over watered will help a lot, but many greenhouse growers keep an oscillating fan running throughout most of the colder months.
One of the most common mistakes new growers make is watering plants according to a set schedule. A number of variables dictate when plants need watering, with temperature, humidity and the growth stage of the plants themselves having a huge effect on how much water is needed.
While in the middle of winter you might only need to water a seed bench every 10 days, during summer the frequency will be increased. The best way to know when to water the plants is to measure moisture in the soil, either with specific moisture metres or just by sight and feel of the soil.