Economics of Growing Greens by Artificial Light

We had a thought the other day about growing greens like lettuce, spinach, swiss chard, and kale inside during the winter months.  What would it cost us to do that, in the limiting case that the greens would get no natural light through our windows?  (Thats actually not too far from the truth--most of our windows face north or are shaded for all but a few hours a day.)

We went back to take a look at our aquaponics setup, which makes use of four 4-foot-long T8 fluorescent light bulbs, and which we used to grow some swiss chard, thyme, basil and dandelion greens at our old place (there were other plants, too, but those were the four that grew fast enough to give appreciable yields).  We were pretty satisfied with the amount of greens we were able to produce from that little 48" x 24" area, but we never actually crunched the numbers on the economics.  So, today we decided to do a quick calculation to see how much it was costing us to grow all those greens, at least as a ballpark figure.

A picture of the working aquaponics grow bed at a young age.  Later it would look much bushier.

The lighting system uses four 32-Watt bulbs, and our electricity rate is about $0.13/kWh. That is, it costs us thirteen cents to consume 1,000 Watts for one hour.  Watts are actually a rate of energy consumption--Joules per second--but total energy consumed is what gets billed.  So instead of doing the logical thing and using Joules as a standard unit, utility companies use the convoluted unit of kilowatt-hours.  Add that to the list of science-business conventions that dont make sense.  But at least its based on the metric system!

So, when the four bulbs are all lit up, were consuming 128 Watts (or 0.128 kilowatts).  If we run the lights for 10 hours a day, we consume 1.28 kWh of energy, which costs us $0.17. (Differences in rates for peak hours, sales tax, and all the other junk the utility company charges for are included in that number.)  Seventeen cents per day doesnt sound too bad.

In the aquaponic system pictured above, we had four swiss chard plants among the other stuff, and were harvesting about 0.1 lbs of chard /week total based on our records, which works out to about 1 lb from those four plants over a 60 day period, or $9.97/lb. (!!)  Not nearly up to expectations, but keep in mind that chard wasnt the only thing in the bed (so the whole cost of the light cant be attributed just to chard), and since our fish were stubbornly refusing to grow, these plants were extremely nutrient limited.  Fortunately, the thyme and basil that we grew at the same time cost a lot more at the store than chard, so it might all even out.  

 But, just for kicks, what would the cost be if we filled the grow-bed with dirt, planted all chard, and it grew a little closer to expectations?


We can assume that ten swiss chard plants will fit in the grow-bed since we had four plants in less than half the space.  A generally-accepted representative time-to-harvest for swiss chard is 60 days, although its usually possible to start selectively eating the leaves well before that (which we did).  But if we take a 60-day baseline, and equate one plant to one bunch that youd find at the grocery store, wed have 10 bunches in 60 days.  So, the calculation then becomes $0.17 per day, times 60 days, divided by 10 plants to give $1.00 per plant (or bunch).  Considering that we currently find it for around $1.99/bunch at the grocery store, that seems like a much more reasonable deal.

Generalized equation to figure out the cost of growing a plant under artificial lights, assuming the artificial light is the only cost.  For "C," use the inverse of the number of plants in the bed (e.g., if you had 10 plants in one bed, use 1/10).  Similarly for "G," if you got, e.g., 8 pounds from 10 plants, use 10/8.

Looks like it might be worth giving it another shot at growing some winter greens indoors!  Next time well use real dirt, and wont count on a few anorexic minnows to provide all the fertilizer.  And now that spring is on its way, we probably wont get to this experiment again until the fall, but hang tight!  We wont forget!


Do you grow your own greens indoors during the winter?  How cost effective is it for you?  Let us know in the comments section below!

Frozen Wild Greens Recap and New! Liquid Carrots for Dessert

When Katies out of town, as was the case this last week, the kitchen experiments around here tend to get a little more curious.  In particular, the opportunity exists to use up things from the freezer that arent allowed in the kitchen at the same time as Katie.  Not that shes particularly picky, but its been a busy week nonetheless.

First, the last of the frozen wild greens are now used up.  There were a couple quart bags of dandelions and one of sorrel in the freezer.

If memory serves, one bag of dandelions was blanched before freezing, and the other just soaked to extract the bitter taraxinic acids, then frozen without blanching.  Both seemed to be functionally equivalent to frozen spinach, except slightly bitter (in a good way).  In the future, we definitely wont bother with the blanching!

The sorrel also seemed to be functionally equivalent to frozen spinach.  This one we didnt blanch because heating the fresh sorrel makes it turn a weird green-gray color.  Interestingly, after it came out of the freezer, it stayed green in the frying pan.  There was only one bag of sorrel, though (no replicate in this experiment!), so well have to try again next year to try to reproduce the lack of color change on heating.

One staple dish around here for frozen greens is a a mix of the sauteed greens, potatoes, plain yogurt (or sour cream if youre trying to get some extra calories in), and seasonings.  Pretty good stuff.  The combination of bold flavors also makes it a good hiding place for odd cuts of meat that some of the Homestead Laboratory resident scientists would object to eating as a featured course.

...such as this delectable bit, which was just as tender and scrumptious as the Curious Coconut promised.  Any guesses what it is? (Hint: click the link.)

An approximate total recipe for this iteration of the dish is something like 10 oz greens, 5 cups cubed, cooked potatoes, 1 lb cubed meat, 2 cups plain yogurt, and salt, pepper, onion powder, garlic powder, basil, and cayenne pepper to taste.  Topped with some melty cheddar, its a dish fit for kings.  Or at least, the king of this castle when the queen isnt around.

Were also big fans of cramming vegetables into our desserts, although Katie tends to be less excited about untested combinations.  For example, the picture shows the makings of a carrot-apple cider-caramel ice cream smoothy.  It took about three medium carrots (which the kitchen scale said was 5.65 oz), about 1.5 cups apple cider, and three big scoops of salted caramel ice cream.  Carrots got chopped in the food processor with the apple cider, then ice cream jumped in and everything got processed until smooth.  Before you wrinkle your nose, keep in mind that carrot juice and apple juice are no strangers to each other in the juicing world (search carrot apple juice to find a litany of recipes), and apples and caramel are one of the best flavor combinations of all time.  (And that is a scientific fact!)  It actually tastes mostly not like carrot.

Thats a big, tall glass of yum, right there.  Yup.

What kind of experiments have you been working on in the kitchen?

Wild Greens Nutrition Comparison

You might be getting tired of all our posts this spring extolling the virtues of wild greens, but we wanted to do one more before giving it a rest for a while.  In particular, we were curious to see how the nutrition of the greens we forage stacked up against the greens we grow, so we made a spreadsheet (of course) to compare.  And as long as we were answering our own questions, we figured we might as well write it up into a blog post!

Its a bit of a challenge to get an apples-to-apples comparison because not all "weeds" have nutrition info readily available, and of the ones we were able to find, not all of the same metrics were available for each (for example, some were missing vitamin K or some of the B vitamins).  On top of that, some of the benefits of eating wild greens are attributed to factors that arent quantified in normal nutritional analyses, such as content of phenolics, flavonoids, and mucilaginous substances. But, for what its worth, we can make a few legitimate comparisons.

And fortunately, theres enough data to make some charts and graphs!

First up, Vitamin A.  Actually, first we should say that the reported serving sizes vary widely across our source materials (linked at the end of the post), so we had to do some normalization.  Everything here is based on 100 g of fresh leaves, rather than a one-cup serving.  But back to vitamin A: just about all of these greens will give you a good dose of it, but if youre foraging and feeling deficient, aim for dandelion, lambsquarter, and stinging nettle greens.  These three, along with kale, are well over the 100% RDV.  Interestingly, several sources claim that mallow is a good source of vitamin A, and although 28 RDV% is nothing to sneeze at, it hardly measures up to most of the other greens.

However, those same sources claim mallow is rich in vitamin C, and the only quantitative measure we could find put it at about 1% RDV. (Although the flowers have a lot more than the leaves.)  But it looks like well have to shoot for dandelion, sorrel, or lambsquarter greens if we catch the scurvy and theres no kale around.

Protein is where the wild greens really start to shine, and finally find a metric where they can beat kale, at least for lambsquarter and stinging nettle.

Similarly, for calcium, the wild greens do well compared to typical cultivated greens.  Stinging nettle blows everything else out of the water, but lambsquarter and dandelion are also higher than anything normal gardeners grow intentionally.  Even the lowly mallow is right up there with kale.

Most of the rest of the items that show up on a nutritional label didnt have data across all eleven species, but if you want to take a look at the spreadsheet, you can find it here.  Also, recommended daily values (RDVs) were based on a 2000 calorie diet.  The RDVs we based our calculations on can be found here.

It would be a shame to spend all this time talking about greens and nutrition and leave you hanging with no evidence of them actually prepared!  So we leave you with this: the dandelion-sorrel quiche we made a few weeks ago should be an excellent source of vitamins A and C!

Did we miss your favorite wild or cultivated leafy green?  Let us know in the comments section below!


Now, the sources of the numbers, in case anyone is interested:

Dandelion, lambsquarter, purslane, and all the cultivated greens came from the self.com nutrition facts database.  In the spreadsheet, when figures were available for cooked greens, we used the no salt option.

Sorrel came from the USDA national nutrient database.

Mallow came from this paper and this paper, using the moisture content to back calculate nutrient content in the fresh leaves.  For the second paper, the moisture content was listed as only 2.8%, which is not typical of fresh green biomass!  So the moisture content from the first paper was used in back calculations of the mineral contents.  Also, vitamin A proper was not given, so the total carotenoid content, which provides an upper limit on the possible vitamin A content, was used.  Also, some interconversion between mg and IU was required for vitamins A and E, which we got from here and here.  Finally, note that the two papers analyze different species of mallow (Malva sylvestris in the first and Malva neglecta Wallroth in the second), so there is some uncertainty in the numbers reported here.  This paper also appears to have the data were after, but only for a price.

Stinging nettle came from this paper, using the spring data because in the fall, there are so many other things to eat.

EDIT 10/19/15: A recent article (covered also here) took a more sophisticated approach, but came up with chard and spinach ranking much higher than kale, which was on par with dandelion greens.  Evidently, they were able to find more complete nutritional data than we did, but they also mention that their ranking system is similarly limited by lack of data on things like phytochemicals.  But we also wanted to mention that watercress, which topped their list, is an excellent wild green, too!  Now if only they had included some of our other favorite wild greens, they would have a perfect article...

Super Greens are Super Food

Super greens and power greens.  They are all the rage with foodies and nutritionists alike right now.  Everyone is crazy for kale.  I like kale as much as the next person (I even have loads of it started right now) and I have high hopes that kale can be my next chard.

By "next chard" I mean a plant that sprouts easily, thrives in the aquaponic environment, and produces an abundance of edibles.  Since the fall, we have been enjoying an abundance of chards.  We have the traditional Fordhook chard as well as the Bright Lights colored Swiss chard.  As usual, the seed from Southern Exposure had a germination rate of almost 100%.

I admit to sprouting the chard seeds in soil and a wicking bed I rigged up, but once they hit the auqaponic systems they took off.

Chard in NFT Tubes on A-Frame

Bright Lights Chard in DWC raft

Chard in expanded clay media bed, flood and drain

While they seem to have done best in the NFT tubes, they performed well using all techniques.

I have been harvesting with a "cut and come again" strategy.  This means I dont harvest the entire plant at once.  I harvest the lower leaves and the plant continues to grow from the top.  This explains the odd growth pattern you may see in the pictures. The stem may start growing a little crazy, but the plant continues to produce new leaves and that means more for us to eat.

It means so much to eat that I have been stretching my culinary capabilities to find new uses for chard.  Chard pizza anyone?  It was actually quite tasty.  I wilted the red chard before baking it on the pizza.  Chard frittata?  It made a yummy brunch.  Of course sauted chard, boiled chard, chard wilted with bacon, chard and cornbread. Chard has made its way into just about everything but the Cheerios.  But if they keep going this strong, the Cheerios might be next.

Seriously, if you are going to the trouble to grow your own food, why not make it something that will pack a nutritional punch.  Chard has at least 13 flavonoids. One of the primary flavonoids found in chard is syringic acid. Syringic acid has recently received special attention due to its blood sugar regulating properties. It has been shown to inhibit activity of an enzyme called alpha-glucosidase. When this enzyme gets inhibited, fewer carbohydrates are broken down into simple sugars and blood sugar stays steadier.  This is important to anyone that is concerned about diabetes, weight control, or eating low on the glycemic index.

Chard also is rich in betalains, just like its cousin the beet.  This phytonutrient has antiinflamatory, antioxident and detoxification properties.  Chard as a beauty product?  Sure, if we are what we eat, why not eat something rich in vitamins A and K so that healthy skin starts from the inside. Chard packs a punch of vitamin C as well.  If you are fearful of the oxalic acid found in chard, be aware that it is concentrated in the stems.  So, all you have to do is add the stems first (so they will cook longer than the leaves) as heat destroys the oxalic acid or if you are eating the chard raw, just discard the stems. 

Got any good chard recipes?  What is the super survivor in your garden right now?