Advice on Greenhouses
A Greenhouse is an asset to any garden. Essential for the propagation of seeds and plants, the features of a Greenhouse provide suitable growing conditions for a wide range of plants, which would otherwise be unable to survive in an external environment.
In order to obtain maximum benefit from a Greenhouse, it is necessary to acknowledge certain details when embarking on the Greenhouse construction. This will help you understand how to equip and work within your Greenhouse better.
Positioning the greenhouse
Positioning your greenhouse correctly is crucial for ensuring optimal light conditions, which directly affect plant growth and productivity. Ideally, you should choose a sunny location that receives bright, unobstructed light throughout the day. This means carefully assessing the surroundings to avoid shadows caused by tall trees, boundary fences, or walls. These structures can block sunlight and reduce the effectiveness of your greenhouse, particularly during the shorter, less sunny days of winter. It’s essential to consider how much sunlight the area receives year-round, not just during the peak brightness of summer.
For a lean-to greenhouse, a south-facing position against a wall is highly recommended. This orientation ensures maximum exposure to sunlight while also utilizing the thermal properties of the wall, which can retain and radiate heat, helping to stabilize the temperature inside the greenhouse.
On the other hand, free-standing greenhouses perform best when oriented east to west. This alignment optimizes sunlight capture throughout the day and minimizes the “lattice blind effect” that can occur with conventional apex structures. An east-to-west orientation is particularly beneficial during winter and spring, as it allows the greenhouse to harness the lower angle of the sun, ensuring your plants receive as much light as possible during these critical growing seasons.
Shading
You can control the amount of sunlight coming in through the Greenhouse materials by the use of shading.
Pull-down blinds with strips of reflective aluminium are popular and easy to use, as an alternative to the traditional wooden slatted blinds.
For a small greenhouse, you can instead use a ‘paint on’ shading liquid that will last the season or shade netting that is fitted over the structure during the high season.
Once you have grown your plants a little, they need to be hardened off before going out into the garden. This means not giving them a shock by going from the hot into the cold, so incorporating a cold frame is ideal. This can be an independent structure or one designed during your greenhouse construction.
Materials for the structure of the greenhouse
When selecting materials for the structure of your greenhouse, the choice typically comes down to wood or aluminium, though budget-friendly options made from alloys or plastic are also available, particularly for hobbyists and amateur gardeners. Each material has its own set of benefits and considerations, which should align with your priorities, budget, and the aesthetic of your garden.
Wood is a traditional choice and often appeals to gardeners who value a natural and classic appearance. It can enhance the overall aesthetic of a garden, blending harmoniously with its surroundings. However, wooden frames require more effort to maintain. Periodic treatments to prevent rot, warping, or damage from weather and pests are necessary, making it a commitment for those who prefer a low-maintenance option. Despite these requirements, well-maintained wooden greenhouses can last for decades and add a timeless charm to your garden.
Aluminium greenhouses, on the other hand, offer a more modern, practical alternative. They are highly durable and require virtually no maintenance, making them an excellent choice for gardeners who prefer convenience and longevity. Aluminium frames are also much thinner than wooden ones, which minimizes the amount of shade they cast and allows for better light penetration. Many aluminium greenhouses are powder-coated in a variety of colors, providing the option to customize the structure to suit your garden’s style. This coating not only enhances the appearance but also helps the greenhouse blend seamlessly into its environment, particularly if it is visible from your home. Aluminium’s lightweight yet sturdy nature makes it a popular and versatile choice for greenhouse construction.
For those on a tighter budget or who need a smaller, more portable structure, greenhouses made from alloys or reinforced plastic may be worth considering. While they may lack the longevity and sturdiness of wood or aluminium, they are often more affordable and easier to assemble, making them ideal for beginner gardeners or temporary setups.
What temperature to heat your greenhouse to?
A Hartley Botanic Tradition 6 plant house
To make the most of a greenhouse it is advantageous to use additional heat.
For smaller greenhouses, it is best to invest in an electrical fan heater with a thermometer switch, in order to achieve the desired temperature.
Many commercial structures often use blown heat, but for large domestic Greenhouse structures, a hot water pipe system with a boiler powered by either gas or oil is the norm.
Thermostats for the system should be located at plant height near the centre of the Greenhouse, where they are not influenced by drafts or sidewall cooling and are protected from direct contact with sunlight and water.
These devices are usually energy saving too. Even simple models can provide different daily temperature settings, which automatically lower the night temperature of your Greenhouse and then raise it in the morning.
Ventilation
Often the sun’s rays can cause the greenhouse to become overheated between spring and autumn, which can lead to plants becoming stressed.
The easiest way for hot air to escape is via roof ventilation, which can be installed during your greenhouse construction.
The cooling process is further improved with the use of louvered vents that open in the sides of Greenhouse. Automatic ventilation can also assist in providing stable temperatures.
A calculation of 25% of the floor area will ascertain the minimum amount of opening vent space that is required for your Greenhouse. Remember, if you feel uncomfortable in your Greenhouse, then so do your plants. These extra Greenhouse details help ensure your structure maintains optimum growing conditions.
Computer controlled heating and ventilation
When choosing a greenhouse keep in mind that, for larger greenhouses, there is an opportunity to utilise a computer to control the heating and ventilation.
This will have been initially programmed so each relevant sensor has been named, sited and numbered. The various required limits will have been entered to allow the system to work.
It is likely there will be different requirements to the use of the heating and ventilation controls during the course of the year.
Alteration of the set points on the computer programme will allow the glasshouse environment to be adjusted, in order to suit the crop being grown at any given time.
It is possible to make adjustments and cross-reference the changes so that there are no conflicting settings within the programme. For general purposes, the control programme will use Day/Night settings.
It is recommended a printout be taken of alterations throughout the year as a record, and also as a guide for future requirements.
Greenhouse layout
Your layout can have a big impact on the growing conditions of your structure. Choosing the best Greenhouse layout is important for creating a comfortable growing space for your plants.
Walls
Hartley Vista lean-to greenhouse
Consider utilising the walls of your structure when deciding on your layout.
Many plants can be grown against the back wall. Fruit is a popular choice, producing a large crop in a small space using traditional fruit training techniques.
Ornamental plants can also be grown in this space e.g. Pelargonium, as well as any number of climbing plants from warmer climates, such as Bougainvillea.
Benching
When planning your layout, some form of benching or staging is essential. Benches provide an area to support growing plants and potting.
The staging needs to be strong and capable of supporting the heavyweight of pots, laden with plants and moisture.
Freestanding benching is one of the most popular greenhouse features and can be constructed of slatted wood (cedar) or aluminium. Aluminium staging has the advantage of longevity and requires no maintenance.
Benches should not be too wide and stand about the same height as a kitchen worktop (roughly 90cm).
Ensure they are level and there is enough room for access and to undertake work on them, fitting within your Greenhouse specifications.
Many garden greenhouse manufacturers produce ornate staging and shelf equipment specially made for particular Greenhouses, however, there are also independent manufacturers that supply ranges to fit all Greenhouses.
Capillary matting
Capillary benches are widely available and can be easily incorporated into your layout. They allow crops of similar plants and pot sizes to be kept evenly watered throughout the day.
They are constructed using a normal flat bench with 5cm-raised edges. The surface is then lined with capillary matting, which goes over the side of the bench into a vat of water.
Capillary matting will draw up water and remain damp so that pots placed on the surface will maintain a steady moisture level.
Liquid fertiliser can be added to the water vat, automatically feeding and watering the plants.
Lower benches are handy for those plants that are resting, such as corms e.g. Cyclamen and tubers e.g. Achimenes (hot water plants).
These added details are also convenient for storing items such as watering cans, sticks for plant supports, and spare pots.
High Level Shelving
Robust staging & shelves in a Hartley Tradition 6 greenhouse
A high-level shelf in your greenhouse is ideal for orchids as this can mimic their natural environment, as they usually grow in trees. It is best to make sure the pots are well balanced so they will not fall off when watered.
Propagator and propagating benches
Propagators and propagating benches are essential tools for gardeners aiming to raise plants from seeds or cuttings, especially in a controlled greenhouse environment. Small, individual plastic propagators are particularly well-suited for greenhouses with limited space, providing an efficient solution for germination and propagation without requiring large setups. These units are typically equipped with propagating trays that feature soil-warming cables embedded in their bases. These cables are connected to a standard electrical supply and regulated with a built-in thermostat, allowing the gardener to adjust and maintain consistent temperatures as needed. The bottom heat provided by these cables accelerates seed germination and promotes successful rooting of cuttings.
For those with more space or specific requirements, constructing a custom propagator tailored to your greenhouse is a practical and rewarding option. A DIY propagator can be built using a wooden frame with 10 cm-high sides. The base should be lined with a piece of 25 mm polystyrene covered with polythene to provide insulation and water resistance. Soil-warming cables are then laid on this base and covered with approximately 40 mm of coarse sand. This setup not only distributes heat evenly but also creates a stable and warm environment for pots and trays placed on the sand. The cables must be connected to a thermostat and electric supply according to the manufacturer’s instructions to ensure safe and efficient operation.
To enhance this arrangement, particularly for propagating cuttings, consider adding a fine mist spray system controlled by a moisture sensor. This system helps maintain the necessary humidity levels and prevents cuttings from dehydrating, which is critical for their survival and development. The misting system also improves the success rate and rooting speed of cuttings by maintaining optimal moisture and reducing the stress on delicate plant tissues.
Both small plastic propagators and custom-built benches offer significant advantages for plant propagation, and the choice depends on your greenhouse size, budget, and propagation needs. Whether you opt for a ready-made solution or a personalized setup, incorporating these tools can greatly improve your ability to grow healthy plants efficiently.
Cleaning the greenhouse
A three quarter span Hartley Lean-to glasshouse build against a stone wall.
Regular cleaning of the greenhouse is an essential maintenance practice that ensures a healthy growing environment for your plants. By adopting thorough and consistent hygiene practices, you can significantly reduce the risk of overwintering pests, fungal spores, and plant diseases that could otherwise compromise the health of your crops. Cleaning not only prevents these problems but also creates optimal conditions for plant growth, ensuring better yields and healthier plants.
To effectively clean your greenhouse, start by removing all debris, including old plant material, dead leaves, and any leftover pots or tools that may harbor pests or pathogens. Pay special attention to corners, joints, and crevices where insects and fungal spores often hide. Once the space is cleared, clean all surfaces, including the glass or plastic panes, structural frames, benches, and flooring. For best results, use cleaning products specifically designed for greenhouse maintenance, as they are formulated to be effective against common greenhouse pests and diseases. Always follow the manufacturer’s instructions for dilution and application to ensure safe and effective use.
Disinfecting surfaces is also crucial. A good disinfectant will kill harmful microorganisms that can linger on greenhouse surfaces. Products such as horticultural disinfectants, bleach solutions, or organic alternatives can be used, depending on your preference and the materials in your greenhouse. Be sure to rinse thoroughly if needed, especially if plants are to be placed in the cleaned area soon after.
Don’t forget to clean other greenhouse features like propagators, pots, trays, and tools. These items can carry diseases and pests if not properly sanitized. Use a brush to remove soil and residues, then soak these items in a disinfectant solution before rinsing and drying them.
Lastly, ensure good ventilation during and after cleaning to help dry surfaces and reduce the buildup of moisture, which can create a breeding ground for mold and mildew. Regular maintenance not only keeps your greenhouse looking tidy but also contributes to a more productive and enjoyable gardening experience. Frequent cleaning—at least annually or biannually—is recommended, with additional touch-ups throughout the year as needed.
By Barry Holdsworth.
www.barryholdsworth.co.uk
Garden Designer & Horticultural Consultant