This is Page 3 of our eight page series on hydroponic flood and drain systems. Click any of the links below to jump to that page.
A variation on a theme: a small commercial all-in-one flood and drain system, available from online hydroponic suppliers. Note the thin black tubes going into each container; they deliver nutrient solution. The containers then drain directly into the reservoir. This particular system is set up with hydroton growing media but this approach would work with any growing media which also suits the intended plants. Also note the eight separate containers, rather than one large container. Having multiple small flood and drain containers allows different plants and/or different ages of plants to be grown together. Planting, pruning and harvesting in one container will not disrupt the rest.
The short answer is that most, if not all crops, can potentially work well with flood and drain. As we've already seen, sometimes the details become really important to achieve that success, so let's look at some caveats.
The general mechanism of flood and drain very closely approximates the natural conditions in which plants originally developed, so the plants don't have to work very hard to get the nutrients they need. That is one of flood and drain's strengths. With that being said, some crops will present challenges to a flood and drain system, not so much because of the irrigation method but because of the limitations for the container, the growing media, the drain system, etc. For instance, root crops such as onions, carrots, rutabagas and the like will very much appreciate the ebb and flow nature of the irrigation cycle, particularly since this class of crops often has a poorly developed feeder root system. The only issue becomes the depth of the container, and whether that depth is sufficient for good crop development. Carrots and rutabagas need at least 12" of depth for good root development, which may not sound like a lot, but that's a big container for confined spaces. Given that root crops are often the cheapest of all produce to purchase, and given that hydroponic growing space may be at a premium, higher value crops might be a better choice. Another consideration is the growing media preferred by the plant, versus the growing media which works well for the system. To use carrots and rutabagas as examples again, they would do very well growing in sand, if the ebb and flow container was big enough. However, that is an extremely heavy setup, and would not be allowed or even safe in some types of dwellings such as apartment buildings. Using lighter growing media could work, but may also result in rather funky root shapes. So root crops in flood and drain systems would only be feasible if a) the growing containers are located at ground level, and b) there are not other, higher-value crops to be grown in limited space.
The issues involved with germination and transplanting crops into and out of ebb and flow systems has already been covered above, so we won't rehash that here. Happily, relatively easy workarounds exist for germinating plants elsewhere, such as in rockwool grow cubes, and then transplanting them into an ebb and flow system for the bulk of their life cycle. One interesting twist on this idea, however, is to use a dedicated flood and drain container specifically for germination purposes, then transplanting young plants out of the germination container and into a different ebb and flow container for further growth and development. Older gardening books talk about having dedicated seedling beds which are specifically managed for germination. They might have a cold frame over them or other climate control to aid in creating favorable germination conditions. Then as the seedlings develop a root system, they are lifted (several of my gardening books talk about "pricking" them out of the seedling bed) and transplanted elsewhere. The same system could be used with flood and drain. The seedling container could be filled with a growing media favorable to germination, perhaps sand, perlite/vermiculite, coir, rockwool grow cubes or some combination. A very shallow and frequent irrigation cycle could be set up which kept the bottom watered but didn't reach the growing media surface, so that small seeds weren't displaced by the irrigation cycle (or just put those small seeds in the rockwool cubes). Then as the seedlings grow, they are gently lifted out and transplanted into a different ebb and flow container, which will have the growing media better suited for long-term development. It's an appealing idea.
Now let's look at some plants that do extremely well in ebb and flow. As we discussed above, anything that has been germinated into rockwool cubes can be transplanted into ebb and flow, and thrive from that point forward. Large-seeded plants can be germinated directly in ebb and flow containers to eliminate the need for transplanting. Some crops with a matting or bunching habit, for instance thyme and oregano, can be planted into ebb and flow containers and then allowed to spread. Similarly, anything which needs to be contained so it doesn't impact other plants nearby can do extremely well in ebb and flow containers, without risk to nearby plantings. Mint, horseradish and other aggressive plants come immediately to mind. And finally, crops which are grown in extremely dense plantings, such as the small grains, will positively thrive in flood and drain systems provided that they are planted into growing media which keeps the small seeds from floating away prior to germination. Rockwool slabs which are cut to fit the container, sand, or gravel would all work well for grains.
On the topic of grains, corn presents some interesting challenges for hydroponics. Most folks would tell you that corn cannot be grown in hydroponic systems. Technically, of course it can. It simply presents some logistical challenges for a hydroponic setup. However, if you have a burning desire to grow corn in a hydroponic system, then flood and drain would be a very good way to do so. First, a mature corn plant is of course quite tall and top heavy. So the container would need to be relatively deep to provide sufficient anchoring to prevent the mature plants from tipping over. Secondly, the growing media would need to be something on the heavier side, for instance gravel, again to provide sufficient anchoring. If those conditions could be met, then corn will grow quite happily in flood and drain systems. One potential setup that would work quite well is to use something like an old metal or heavy duty plastic livestock watering tank, one of the oblong shapes which gives plenty of depth but easy access from either side. We have a livestock tank which measures roughly 6' long by 2' wide by 3' deep, which would be ideal. Fill that 3/4 with gravel and connect the bottom drain back to a nutrient solution reservoir, and voila! A growing container for a small plot of corn.
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