The most useful tool in a greenhouse

Two jobs, one system

A shade screen does two jobs, and it does both of them remarkably well.

The first is shade (when you need it). 

In warm climates with high solar radiation, closing the screen shades your crop the way an awning shades your patio. But as farmers, you need control over when to shade your crops. That’s why we only set up retractable screens. 

These screens, controlled by the greenhouse climate computer, open and close automatically based on radiation sensors and temperature readings. Clouds pass over the sun, the screen opens. The sun comes back, the screen closes. You get the light without the heat stress.

For all that movement across 10,000 m², you're only running a single gear motor. Compared to the alternative - extraction fans, circulating fans, and wet wall pumps running continuously - your electricity bill is but a fraction. The motor turns, moves the screen, and stops. It doesn’t use power while the screen is in place.

The second job is energy conservation. 

Picture your greenhouse at night: the peak of the roof might be six or seven metres tall, but your crop only occupies the lowest metre or two. Without a screen, your heating system is trying to warm that entire volume of air, including the metres of empty space. 

Close the screen, and you effectively divide the greenhouse into two compartments. The warm air is trapped below, around your plants. The cold air sits above the screen, unheated.

That’s why screens typically deliver 30 to 50% savings on heating costs. Some multi-layer installations achieve even more. The screen closes in two or three minutes, and you get the benefit all night long without drawing another watt. In cold climates, you'd struggle to find a commercial greenhouse without one. 

Screens typically pay themselves back in two to four years, and in many cases, less. Just by reducing energy costs.

Choosing the right cloth

The right cloth depends entirely on your climate and your crop.

If you're growing in a warm climate where heating isn't a concern (like parts of Mpumalanga, Limpopo, North and East Africa), you want a permeable, open-weave cloth, because it allows hot air and humidity to pass through the fabric and vent out of the greenhouse. 

If you use an impermeable cloth in a hot greenhouse, you land up trapping heat and moisture.

In cooler regions, the opposite applies. An impermeable, closed-weave cloth creates a thermal blanket effect that seals the warm air below and keeps the cold air above. This is the cloth you want in the Western Cape highlands, the Free State, or any winter production environment.

Beyond open-versus-closed weaved screen cloths can also be engineered to manipulate how light passes through them. 

Some cloths diffuse direct sunlight, scattering it more evenly across the canopy. This is brilliant in glass greenhouses, where direct light through glass panels can cause uneven crop growth. In plastic greenhouses, it’s a great way to upgrade your light quality without replacing your roof cover.

The shade factor varies widely. A 30% shade cloth handles moderate radiation. A 50% cloth suits higher-intensity conditions. The right specification depends on the crop, the climate, and the season.

Why quality matters

A screen system is a mechanical installation with moving parts. It's not like installing a shade net and walking away. The cloth moves back and forth every day, sometimes several times a day, driven by motors and cables that must all work together reliably for years.

That's why the quality of the components and the design of the system matter as much as the cloth specification. Poorly designed slip blocks, loose cable tension, or substandard profiles lead to uneven closure, cloth wear, and maintenance headaches that eat into the savings your screen was supposed to deliver.

We partner with Alweco, a Dutch manufacturer that has been designing and building greenhouse screen systems for over 35 years. They develop many of their components in-house, including the Ultra Lock screen profiles and Ultra Delay slip blocks that ensure a tight seal when the screen is closed. It's a partnership we chose specifically because their engineering focus matches how we approach greenhouse design: get the details right, and the system performs for years without constant attention.

Start with the screen

If you're weighing up climate control investments for a new greenhouse, or looking for the highest-impact upgrade to an existing structure, a shade screen is your best bet. 

The running costs are negligible. The energy savings are immediate. And the right cloth, matched to your climate and your crop, gives you a level of environmental control that matches the gains from far more expensive systems.

We'll help you match the right cloth, the right mechanical system, and the right specification to your climate, your crop, and your budget.

Get in touch on +27 21 987 6980 or info@vegtech.co.za.