Growing spinach in hydroponics is basically a race between the spinach and Pythium. Fortunately for us, the good people of Cornell have done a lot of work figuring out how to help tip things in favor of the spinach. Brief reports here.
First of all, it turns out there’s a temperature tipping point. Above it, Pythium grows faster. Below it, spinach comes out ahead. That temperature is about 20C (68F).
So, the first step to avoiding sudden death by Pythium is appropriate temperature. That’s why it’s very important in aquaponics to match species of plants and fish that grow in similar conditions. If you tried to grow spinach with tilapia– whose favorite temperature is somewhere around 30C (85F)– at least one of those species would be very miserable. On the other hand spinach would probably do very well with some freshwater salmon relatives like trout, Arctic char, or grayling. Spinach and salmonids both like their water bracing and chock-full of oxygen.
So do sturgeon… sometimes. They tolerate cold very well but grow best around room temperature. What cold is good for with sturgeon is cuing them to begin forming eggs. Thus there may be a place in sturgeon-based aquaponics for a cool-water hydroponic plant like spinach (and other winter greens like mâche, radicchio, endive, etc). Being able to nudge a fish to begin the spawning process by imitating natural seasonal cues means that you know when it’ll be ripe. Obviously you don’t want a fish suddenly losing her eggs all over the tank because you didn’t know to milk in time. Another potential problem is that the fish simply reabsorbs the eggs when she decides the tank isn’t a good place to spawn. That can be ok once or twice, but from what I understand it can be bad for the fish’s health if this occurs too many times.
There are some other cool things you can do to help the spinach pull ahead. Fungal and bacterial pathogens grow 24/7. Plants only grow when there’s light. Drawing out the light period can do some amazing things for plant growth– as evidenced by Alaska’s annual summer takeover by giant killer cabbages.
All it takes to grow Cabbage the Hutt is 20+ hours of sunlight a day. Piping in extra CO2 is another way to boost growth. This technique is actually pretty common in the Netherlands where they have to keep the greenhouses sealed up tight to keep the warm air in. The plants can run out of CO2 by mid-morning on a bright winter day if you don’t keep adding more.
Both supplemental lighting and CO2 are quite intensive and not something you’d do for a home garden, unless you simply have to have 93-lb cabbages for some reason. But they do speed up growth enough that they can pay off if you have the right commercial market. The Dutch have done very well for themselves by using these kinds of techniques just to increase yield on their small land acreage. There may well be a place for them in US farms close to urban markets where land is at a premium.
Well, that’s it for today. Moral of the story: spinach needs environmental conditions that push you more towards an intensive, tightly-controlled Dutch-style production model if you were to grow it in one place year-round. The US is large enough that there’s almost always someplace that’s enjoying the right weather to grow it so our markets have leaned more in the nomadic outdoor production method. American growers have been loath to adopt high-production greenhouse techniques. Now you know why you’ve never seen hydroponic spinach at the grocery store– and why that may change as transportation costs go up and local food grows in popularity.