In hydroponics, a continous-flow solution culture have a solution that is constantly moving past the roots. Thus, they roots are not submerged in standing water.
For this type of set-up, it is common to use big storage tanks rather than individual jars or buckets for the plants.
Nutrient film technique (NFT)
The nutrient film technique (NFT) is a method where a very shallow stream of nutrient solution is recirculated past the roots of the plants in a thick root mat. The root mat develops in the bottom of the channel, but the upper surface is above the surface of the nutrient solution (although still moist).
For this set up to work well, it’s important that they parts of the roots that are above the surface has access to plenty of oxygen.
To get everything right, be prepared to make tweaks and adjustments to your original set up, e.g. when it comes to flow rate, the slope angle of the channel, and the lenght of the channel. The aim is to create a situation where the plants get plenty of both water, nutrients and oxygen at all times.
If the water pump that circulates the nutrient solution stops working (e.g. due to mechanical failure or power outage), the situation will quickly become dangerous for the plants. These systems therefore requires constant monitoring.
It can be tricky to find the perfect angle for the slope; one that makes it possible for nutrient films to flow without ponds forming in local depressions. Some experts recomend 1:100 sloping, but slopes in the range 1:30 to 1:40 are common, especially among beginners.
The longer the channel, the more difficult it becomes to make sure that even far away plants gets enough nutrients. If you are a beginner, not exceeding 10 metres is recommended. If you absolutely want longer channels, place another nutrient feed halfway along the channel and decrease the flow rates by 50% through each exit.
A good starting point is a flow rate of 1 litre per minute. Keep an eye on things and adjust it if necessary, to suit your particular set up and plants. Also, if the plants grow big, you might need to increase the flow rate somewhat to accomodate for their larger needs. A flow rate above 2 litres per minute is rarely a good idea (except for exceptional circumstances) since it tends to cause nutritional problems.