We pulled out the refractometer this morning after harvesting arugula and got geeky. Our curiosity was piqued after clearing out a bed of early arugula in the greenhouse and picking from an outside, uncovered bed and noticing subtle and not at all so subtle differences in plant form.
The arugula grown inside is uniform, unblemished, strong green, snappy, yet tender and delicious. The arugula growing in the outside bed is variable. This bed is a sparkly new raised bed built just in front of the greenhouse. We filled the raised bed with wheelbarrow loads of dirt that had been excavated for construction of our new pack shed. Since seeding in this bed, we’ve noticed patchy sections of really poor germination and stressed plants. All other inputs being the same, our best guess is that this is a soil quality/nutrient availability issue. Indeed, this crap sections of the bed are “wheelbarrow load-sized”, where we must have been loading from a poorer section of the excavated soil. Arugula plants in the meh soil, are super stunted (1-2″ tall), with yellowed leaves, and hit hard with flea beetle damage. The arugula growing in the good soil have dark green, broad leaves, limited flea beetle damage, and much better germination.
The refractometer is a tool we use to help determine the optimal time to harvest our grapes. The refractometer measures the dissolved solids in the plant juices, and are a good approximation of the total nutritional value and health of the plant. Higher brix numbers (degrees brix, °Bx) equal more dissolved sugars and generally higher nutrition. With grapes, it’s fun watching the brix numbers climb over the course of a couple weeks, generally in August. For harvesting, we want the grapes to read at 22°Bx. Of course this is typically 12 hours after the robins pillage the vines. A refractometer can also be used for the juices in plant leaves, though we haven’t explored this much. Until today.
This morning we started out with a quick look at a few of the arugula plants in the greenhouse, then out to the uncovered bed. At which point we couldn’t stop, so we went out to test the spinach and lettuce. Our test sample size is puny (3 or 4 plants), but the results have us stoked to look further into this.
Unfortunately for the sake of comparison, we’ve already pulled out the spring greenhouse lettuce and spinach plantings to make way for summer successions (basil, cucumbers and peppers). There are other things to look at. And we’re going to refractometer them all.
Greenhouse arugula readings were very close, 6.5-7°Bx. Please note, this summary is based of off a very (very) few samples. In the greenhouse, we measured brix from three leaves, 3 different plants. We were surprised to see how much higher the outside stunted arugula brix levels were, and then again, how close the brix from the stunted, flea beetle harassed leaves were to the much healthier looking, only slightly flea beetle damaged arugula growing right down the row. The spinach tested were from a bed that had overwintered outside,the variety Winter Bloomsdale. The wide range in lettuce (9-15°Bx) is interesting given these were readings all from one variety, Vulcan (this was a planting from fall 2016 that overwintered). Jeremy has a special thing for lettuce, and grows over 20 different varieties, so there is vast potential for refractomtastic lettuce studies. Look out for our research published in Nature, or maybe Science, with more box and whisker charts.
These measurements were made mid-morning, after harvesting and packing things away. It would be interesting to compare degrees Brix of greens throughout the day. Are brix levels higher early in the morning, while plants are cool? Does this translate to optimum harvest time for highest nutrition content?
We appreciate the greenhouse for early spring harvests and as a refuge from summer hail storms, but looking at this comparison reaffirms our interest in learning how to better grow in accordance with the elements.
Rain and sunshine, t and j