Vertical A-Frame NFT Grow System
Ensure the site is leveled and the base is strong enough to hold the weight of the frame. Laying out a concrete slab is preferable, but expensive and labor-intensive. Instead, consider laying aggregate crushed rocks (G1 to G3) or use a soil compactor to solidify the soil surface. Since the channels will be filled with water, you’ll have to factor in the additional weight.
Angular bars are great for frame materials as they are easy to work with and have a good strength capacity. Coating the bars with an anti-rust primer helps elongate the life span of the frame. In calculating the height and angle of the legs of the isosceles triangle, you must consider the height of your greenhouse, the roof-type, the type of crop to cultivate, and the user comfort in using step ladders. The usual 16 channel A-frame is 10ft x 5ft x 10ftx (L x W x H) and can hold about 350 plant holes.
The NFT channels can be made from locally available PVC, whether round or rectangular (downspouts). The cheapest option is using 4” PVC pipe. Both ends need to be capped with a socket-type female threaded clear-out. Always use Teflon tape to avoid leaks. The usual plant distance is 6 x 6” center to center, but depends on what type of crop you plan on growing. Drilling a hole is easy with a hole saw with shank drill used to drill holes for a lock assembly in wooden doors.
TIP: Use the drill in reverse gear to get faster results.
Painting the NFT channels in white glossy primer is important to reduce heat transfer to the water inside the channels. Also, make sure each channel has enough vertical grow space for the plant to grow unimpeded by the top channel.
The Drain Connectors
The A-frame NFT channel works by routing water in a single direction across every channel and via gravity down to the next level until it returns back to the reservoir. That’s why you’ll need to install drain connectors to link the channel with the channel below it. There are a variety of ways to accomplish this, but the easiest is using a series of PVC elbows and Union Patente fittings.
Drill a ¾” hole in the bottom and top of both channels and create your connections. The insertion height of the drain pipe into the top channel is very important to consider. If it’s too high, the waterlevel inside the channel will drown your plant roots. If it’s too low, the plant might dry out prematurely as it will take a little longer for it to reach the water, especially in our very hot climate. A good starting point is roughly ½” to ¾” from the bottom of the channel, but all depends on your own conditions.
Dig a hole and bury your water reservoir inside the ground for several beneficial reasons. First, it will allow you to add another set of channel layers on your A-frame. Second, it keeps the water temperature cooler than surface temperatures. This is a very important consideration in hydroponics. The water temperature must be lower than 25-28 degrees for the plants to function well. The reason for this is that the solubility of oxygen in water decreases at increasing temperatures. Less oxygen means the roots will drown and rot. The water reservoir serves as your mixing tank where you can add your fertilizer nutrients according to your formula recipes.
Drop a submersible pump to the bottom of the reservoir to pull all the cooler water back into the irrigation lines. The strength of your pump depends on the max height of your A-frame and the number of interconnected A-frames, in any. Installing a strong pump is not always efficient while a weaker pump is useless. Calculate the head pressure and flowrate to find the best pump for your purpose. While at the bottom of the reservoir, the pump also brings up any loose sediment to the lines which ought to be trapped in the line filter.
The filter serves as the collection point for all the sediment and gunk that don’t belong in the NFT system. This can be a disc filter or screen mesh filter, which are both in-line filters with threaded ends for easy installation with PVC connecting parts. For a simple A-frame unit, you wouldn’t need more than a 3/4” screen mesh filter. Be aware to clean the filter every couple days or every week to clear out any debris or algae that might build up in the system. If you’re getting weak flow at the irrigation discharge, that usually indicates a clogged filter.
The Irrigation System
To deliver the nutrients from the filter to the top of the A-frame, HDPE polypipe is a good solution. It’s a durable material, has high compression resistance, and is flexible. It comes with several fittings to extend, elbow, or tee the line into several directions and you can add in several valves to isolate areas for future maintenance. If you are connecting several A-frame NFT systems in series, you should consider using microtubing with microtube adapters connected to the main polypipe to equalize discharge pressure across the entire line.
One of the most overlooked considerations of using a vertical A-frame NFT system is the trajectory of the sun across the sky during the day time hours. Be mindful of any shadows from nearby trees or structures that can affect your plants. Likewise, if your greenhouse is located in an open spot with lots of direct sunlight, you have to consider the proper orientation of the A-frames relative to the sun’s path. Since the A-frame is essentially an isosceles triangle, you have to make sure both sides will receive ample sunlight for the plants to grow equally. If only one side of the frame gets all the sun, then as the front seedlings grow bigger, it starts to shade out the seedlings on the other side of the frame. This will result in unevenness of plant growth across your frame.