Green Roof Food Productivity by Variety by Zane Pace

Our focus this month has been on harvesting the winter crops we planted last semester, and identifying our top performers. Plants were harvested continuously over several week period, sorted into marketable and non-market categories, and weighed for biomass. We generated data on establishment, survival, productivity, and marketability % for each crop. I was fortunate enough to be allowed to analyze the data myself, and to present our findings with Nicole Forbes at Texas A&M’s Student Research Week this year. Unfortunately, it turns out that I get maybe a little too into data analysis, and SRW posters only allow for the presentation of so much data, so a lot of the graphs and comparisons I churned out wound up not getting included. Fortunately, I know just where to present the bits I had to omit from the poster. Here.

First, I’ll give you a quick and dirty posterview (portmanteau of poster and overview, duh) to relate the general results. From a survival perspective, everything was pretty positive, with the exception of root crops like turnips and beets. Leafy greens and herbs are definitely viable for green roof production. Of those we were able to harvest for this data, Kale, Lettuce, and Parsley were the most productive. What I didn’t get to include, however, was the variation among different strains of these crops, which was considerable.

While we looked at the overall crops for their productivity, each of those includes several varieties, each of which produced at different levels and fared differently on the green roof. I can’t be sure why this was the case, but the intracrop productivity splits were apparent enough that I wanted to investigate them. I did so by charting the relative contributions to a crop’s total marketable biomass by each variety, or varietal market share.

Lettuce provides a nice starting point, because it displayed a very even varietal split. With only two varieties, it is also the most basic case. We planted the same number of both Butterhead and Romaine lettuce, and establishment was identical for each. They each produced about the same amount of marketable biomass too, so the split is almost 50/50. This is expected.


Parsley getting a little less even

Parsley exhibited a slightly different share split. 3 parsley varieties were planted, including Italian Plain, Curly Leaf, and Italian Giant. Of these, the Italian plain produced 50% of the marketable biomass, while curly leaf and Italian giant generated 28 and 22 percent, respectively. I don’t have an explanation for this difference, but it is a significant split relative to that seen in lettuce.

What is Red Russian Kale doing with its life?

The Kale is the one I really want to discuss, however, because it has an extreme varietal split. We planted Beira, Toscano, and Red Russian kale varieties. All of them grew and survived at high rates. However, beira kale produced a full 73% of the marketable kale biomass from the roof, while red Russian accounted for only 5. Toscano was 22%. Part of this split is due to differences in leaf size and shape among the varieties. Beira grows wide, large leaves more similar to those of lettuce, while red Russian and toscano produce the long, slender leave you might typically associate with kale. Hence, Beira leaves just account for more biomass. However, the splits were further driven by flaws in the other varieties. Only 28% of the red Russian was marketable, compared to 73% for beira and 98 for toscano. The reason for most of this was bugs. Red Russian kale leaves that were otherwise perfectly fine had to be rejected due to the loads of aphids they attracted. Aphids that didn’t appear on any other plants on the roof. I have no idea why these bugs seem to love red russian kale alone, but they seriously compromised large proportions of an otherwise fine harvest, and should be accounted for in any future green roof farming projects.


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