10 Tips For Greenhouse Gardening Success

Having a greenhouse opens up a whole host of new gardening horizons, many of which welcomed by the seasoned gardener and daunt the newbie looking to enter the world of gardening. The biggest advantage of a greenhouse is that it allows you to grow plants and crops that require more shelter and higher temperatures than your open British garden. Greenhouses act as magnificent season-stretchers allowing for earlier springs and extended autumns. Greenhouse gardening can be extremely rewarding, think tomatoes, peppers and aubergines in the summer followed by hardy oriental greens in the winter. For those new to greenhouse gardening and for those who would like to brush up on their technique we have put together 10 helpful tips to get you on your way to greenhouse gardening success!

#1 Choosing Your Greenhouse

Greenhouses come in a variety of different sizes and shapes, from simple cold frames to show-stopping bespoke greenhouses and depending on your needs your greenhouse may require additional extras such as; heating, staging, shelving and lighting. Such extras allow you to make the most of your greenhouse, a heating system, in addition to solar heat, will enable you to grow almost anything all year-round. An electricity supply is highly beneficial as this means you can install a number of amenities such as lighting, having lighting means you can visit your greenhouse at night and when levels of natural light are low.

You will need to think about what you want to do with your greenhouse, if you work and you can only tend to your greenhouse around you work hours installing a lighting system would be hugely beneficial whereas if you’re looking to work all year round a heating system would be incredibly beneficial.

#2 Planning Your Layout

Getting your greenhouse layout right is paramount for optimum efficiency, a cluttered and confusing layout will only lead to rising stress levels and falling plant pots. You will need to measure your greenhouse and work out how much space you have for beds and growbags, make sure you have enough space for all the summer greenhouse crops you intend to grow.

Benches/Staging should provide plenty of space for seedlings, many of these will be moved outside when the space is needed for summer greenhouse crops. Your staging needs to work around you and cater to your needs, your staging should stand at comfortable working height to avoid any strain and back ache. Shelving at eye-level or just below work well if you have plenty of height to play around with, this allows for plenty of space above the benches and easy viewing/maintenance.

Below is a great example of a well-thought-out greenhouse layout, note how all the available space is being used effectively for optimum efficiency.

10 Tips For Greenhouse Gardening Success

#3 Temperature & Heating Control

When it comes to heating your greenhouse heaters, vents and fans are your allies in controlling the temperature in your greenhouse. Despite your best efforts to make your greenhouse solar-efficient the outside conditions will ultimately influence the temperature of your greenhouse, during periods of cold weather and cloudy conditions an additional heat source will be required to keep plants growing at an optimum rate.

The ideal temperature inside a greenhouse should be between 27-30 degrees Celsius, so the first and most important lesson is to learn how to maintain and steady temperature inside your greenhouse. Greenhouses mainly rely on solar heat to heat the interior air, when this isn’t possible there are a variety of options to supplement the heat you will need to make sure you have either a gas or electric supply to power the heaters. To monitor the greenhouse temperature you will need to have a thermometer as just like a car, the greenhouse’s interior can quickly heat up to over 38 degrees Celsius on a warm sunny day risking stressing and perhaps killing your plants.

Your greenhouse temperature will be dependent on the types of plants you plan to grow, you will need to match your heating system to your plants’ needs.

#4 Ventilation

Your greenhouse must include vents, either a top vent that opens a hatch in the roof of the greenhouse or a side vent and fans that whisk out hot air and usher in cooler air. Dependent on your amenities you have the option of manual vents or automatic, automatic vents and fans will require an electric source. Manual systems are cheaper, but you will need to remember to physically open and shut the vents or prop open the greenhouse door during the day and close it at night. This option doesn’t work for everyone, especially those who aren’t at home during the day as our unpredictable british weather can suddenly change and you will need to adjust your vents to suit the weather, not possible if you’re at work or unable to get to your greenhouse.

An automatic ventilation system works on a sensor that triggers the fans or heating system if the temperature rises or falls below the threshold that you have programmed into the system, similar to how a home central heating or air conditioning system works.

Getting your ventilation right is vital for plant health, good air circulation strengthens the woody tissue in stems and decreases the opportunities for fungi to attack your plants. You need to leave adequate space between plants and keep on top of pruning so that the leaves from adjacent plants don’t touch each other. Dense plant growth can interfere with air circulation and contribute to excessive humidity.

Plants use carbon dioxide from the air to manufacture sugars to aid their growth, in a poorly ventilated/closed greenhouse, carbon dioxide can be depleted and therefore plant growth is slowed. Try to get as much fresh air in as possible each morning to encourage healthy plant growth.

Top Ventilation Tips:

  • Prop open the door on warm days. Be sure to secure the door to prevent the wind from slamming the door shut.
  • For cold frames, prop open the lid of the cold frame during the day to allow air to circulate.
  • Use additional stand fans as needed to keep the air circulating.

#5 Controlling The Humidity

Hot and humid greenhouses that feel more like a rainforest do not produce strong, healthy plants. Humidity and temperature are very important factors but ones that must be measured carefully and too hot or too humid can inhibit your plants growth and provide a thriving environment for fungal disease.

Humidity offers many benefits, particularly to tropical plants, humidity levels should be between 50-85%. At levels of 90-95% plant growth is weak, early bolting occurs, and fungal diseases become a real problem. If you experience too high levels of humidity you need to increase ventilation and watering your plants only when necessary.

To increase the levels of humidity you can place trays of pebbles underneath the plants, fill the trays with water so it covers the pebbles. As the water evaporates, it will increase the humidity levels. Alternatively, you can place marble or stone chippings under the benches/staging in your greenhouse and these will create humidity if they are dampened down on a dry day.

10 Tips For Greenhouse Gardening Success

#6 Light & Shade

Light levels in a greenhouse are partially determined by the design and location. When planning the location of your greenhouse, check shade patterns from near by buildings or trees etc. as during the summer months too much shade can inhibit the growth of your plants.

When natural light isn’t in abundance there are a number of lighting options to keep your greenhouse ticking over all year round. Fluorescent lights are a very useful addition if you’re planning to grow spring seedlings, these are particularly helpful on cloudy days. For the best results we recommend installing the lights directly above your benches or shelving, this way they are out of the way and not taking up any valuable surface space.  There are plenty of bulb options you can choose from, whether it be fluorescent bulbs designed for plant growth or bulbs that mimic sunlight.

Adding a timer is a great option that will give you control over the amount of light your plants receive without having to worry about turning the lights on and off manually. Timers can be linked to other extras and can also control automated watering and mist systems, fans, and heaters.

Don’t forget that plants can receive too much light as well as too little, especially in summer. This is where shade cloth comes to the rescue, it comes in rolls or green or other dark-coloured material and can be rolled out over the windows to provide shade and decrease the temperature inside your greenhouse.


#7 Soil

Depending on your set-up you can either amend the soils under your greenhouse and plant your plants rights into that soil but more home greenhouse growers prefer to use benches, staging and shelving with individual pots or grow bags filled with a soil mix.

Soil mixes for containers, benches, and beds should be lighter and more fertile than most garden soils. A good soil mix should drain fast, hold moisture well, contain balanced and slow-release nutrients, and have a slightly acidic pH.

#8 Sowing & Growing

When it comes to sowing you must use clean pots and trays and fresh, peat-free seed or multipurpose compost then follow the instructions on the seed packet. The seeds will germinate on a sunny windowsill indoors or in a heated propagator unit in a greenhouse, if your greenhouse is unheated the propagator may struggle to maintain warm temperatures during cold weather.

Once germinated, seedlings will need somewhere light and frost-free to grow on, you must bear in mind that unheated greenhouses may not be sufficiently warm until April. You could use fleecing and heating a partitioned section of your greenhouse to make a suitable environment for growing tender plants. All gardeners must be aware of the weather forecast so make sure you keep an eye on the forecast and be prepared to protect young plants with fleecing on frosty nights or provide supplementary heating when needed if your greenhouse is unheated.

#9 Planting

The final stage and the product of all your hard work so it is important to get this stage right and not to rush it! Plant protected crops into their final positions as soon as they are sturdy and well-rooted, these need to be planted into greenhouse borders, containers or grow bags. Ensure climbing plants such as cucumbers have sufficient support and tie tomatoes to support canes with string.

10 Tips For Greenhouse Gardening Success

#10 Maintenance

Summer Maintenance

  • Check watering daily or install an irrigation system; uneven watering can result in problems such as blossom end rot in tomatoes
  • Ventilate greenhouses on warm days by opening doors and vents; automatic ventilation is the best option if feasible
  • For warmth-thriving cucumbers, vents can be kept closed but humidity must be raised by damping down.
  • Some shading will be necessary; it is best to add this gradually, as it will initially reduce growth
  • Hang sticky insect traps to provide early warning of pests so therefore pest control can be addressed promptly
  • Tie new growth into supports regularly

Winter Maintenance

  • Keep structures, especially glazing, clean and repair any damage
  • Invest in a minimum/maximum thermometer to monitor conditions
  • Fit insulation – bubble wrap or fleecing is sufficient for many structures
  • In heated greenhouses, ensure a thermostat is working to maintain a minimum night-time temperature