Monday, October 03, 2011

Garlic & shallot harvests: ecoroof and yard

The Experiment

Test locations

Last fall I planted garlic and shallots in the yard and on the sunspace and front porch and ecoroofs:
  • Sunspace ecoroof: 5.5" of soil medium. Slight south slope, and heated living space below, full sun. (Photo at left.)
  • Front porch ecoroof: 8" of soil medium. Slight north slope, open air beneath, full sun.
  • Yard: Various locations, all in full sun until about April, but some with morning shade or morning and mid-day shade thereafter.
See my Ecoroof Planting Plan for details on the ecoroof locations and polycultures.

Season conditions

Portland had an unusally wet and cool spring and early summer. This likely benefited the ecoroof plantings by providing low heat stress and enough moisture despite the thin soil and exposed conditions. Meanwhile, the yard plantings suffered from leaf rust and root rot (more details below.)

Uncontrolled variables

I planted garlic cloves 8-12" apart from each other, in various polycultures. I used a wider spacing than the usual 4-6" because I thought the thin ecoroof medium might not provide enough water and nutrients, especially with other polyculture plants mixed in. I created and planted the ecoroofs last fall, so they had few weeds and very young polyculture members. Engrossed in our house project, we did no weeding in the yard, so those plants had to cope with competition from many weeds as well as from nearby established plants, including overstory trees.

As noted above under "Test locations", some of the yard garlic varieties experienced varying degrees of shade from about April onwards.

Much of the yard garlic was planted in spots which have grown garlic in previous years (ie, no crop rotation). The yard garlic all got hit with leaf rust (super common around Portland this year), and some got root rot. The ecoroof garlic did not get either disease. I don't know that the leaf rust harmed the garlic all that much, but the root rot made many plants unusable. I discarded these bulbs from the figures, but some of the bulbs counted may have suffered partial damage.

Several of the garlic varieties I planted in the yard came from first year purchased seed bulbs, which means that I planted many small cloves. We had already grown out almost all the ecoroof varieties for at least one year prior, so we were able to select only the largest cloves for planting there.

I planted the ecoroofs first, and the yard a little later. This meant the ecoroofs had a week or two head start. More importantly, I wound up using the largest cloves on the ecoroofs since I popped cloves for planting as I went. The yard plantings got the smaller, left over cloves.


I expected soil depth (and thus nutrient and water availability) would determine yields. So I expected garlic in the yard to give the greatest yield, followed by the front porch ecoroof, with the sunspace yielding the least. I didn't expect the condition of seasonal shade in some of the spots in the yard to have too large an effect. I expected the interplanting of garlic with other polyculture crops not to affect the garlic too much, since for most of its growing season the garlic has access to full sun, only suffering from some competition starting in May or June.



When I harvested bulbs this summer, I let the entire stalks air dry for about two weeks in the shade of our front porch.  Then I trimmed off the stalk and most of the root, and for each variety and location recorded the number of bulbs harvested and the total weight, to give an idea of weight per bulb. This allows comparisons of the yield in different conditions.


VarietyLocation# bulbsWeight (oz)Weight/bulb

German PorcelainSunspace2422.5.938
German PorcelainPorch1820.251.125
German PorcelainYard65.833Morning shade
Polish JennSunspace1832.251.792
Polish JennPorch1316.251.25
Polish JennYard98.25.917Morning shade
unknown #1Porch69.51.582
unknown #2Sunspace29551.897Minor morning shade
unknown #2Front porch15241.6
Italian LateYard249.5.3961st year seed cloves, heavy competition
Mild French SilverskinFront porch179.25.5441st year seed cloves
Mild French SilverskinYard178.25.4851st year seed cloves, heavy competition
NootkaYard126.25.5211st year seed cloves, heavy shade from hazel
MusikYard11121.0911st year seed cloves?, only light competition
Appalachian RedYard1413.9291st year seed cloves, only light competition
Inchelium RedYard2113.6191st year seed cloves, fair amount of overstory shade
Spanish RojaYard85.6251st year seed cloves, fair amount of overstory shade. May not have found all bulbs (numbers here reflect the 8 bulbs I did find.)
Elephant garlicSunspace832.254.031
Elephant garlicPorch16462.875May have planted smaller cloves
Holland Red shallotSunspace7192.7141st year seed cloves
Holland Red shallotPorch712.751.8211 or 2 duds not counted. 1st year seed cloves
Holland Red shallotYard43.5.8751 planted bulb vanished, not counted. 1st year seed cloves
Dutch Yellow shallotPorch11181.6361 or 2 duds not counted. 1st year seed cloves
Dutch Yellow shallotYardEntire planting of 8 bulbs vanished (perhaps so runty that I just couldn't find them to dig them up? Hopefully they'll resprout this fall.) 1st year seed cloves

VarietyLocation# bulbsWeight (oz)Weight/bulb


I harvested scapes from nearly all the garlic plants. I didn't track which varieties yielded what scape weights, or how many plants provided them, but here's the basic harvest info. I estimated the number of scapes based on number of bulbs harvested (from table above); I know I missed some scapes from the yard so I've adjusted that number down slightly. Also, I have a sense that not all of the varieties made scapes, so these numbers may be off by quite a bit in terms of weight per scape.

Location# scapesWeight (oz)Weight/scape



Locations yielded inversely to my expectations: the yard yielded the least, the porch roof in the middle, and the sunspace the most. I attribute the low yard yields to the increased competition and disease problems mentioned above, especially since the plantings with the heaviest competition do seem to have yielded the lowest amount (though varietal difference could also affect this comparison.)

A friend just reminded me that garlic doesn't like hard soil, which characterises much of our yard soil. So that could also account for the reduced size of the yard garlic compared to the garlic growing in the very light-weight, loose ecoroof soil.

As I recall, all the sunspace growth (garlic and other plants) got off to an earlier start than on the porch roof. I now suspect that the heat from the sunspace room, despite about 14" of ceiling insulation and a 1" air gap, provides enough extra warmth to the ecoroof above to greatly improve plant growth. Alternatively or in conjunction, the south slope of that roof vs the north slope of the front porch roof may create enough of a microclimate difference to account for the improved yields.

I don't know why the German Porcelain garlic performed better on the Porch than on the Sunspace roof, in contrast to the other porch vs sunspace comparisons. Also interesting to note that the morning-shaded yard planting of this variety yielded only 10% less than the sunspace planting. Similarly, the yard planting of Mild French Silverskin amongst heavy competition came within 10% of the yield of the sunspace planting. Other varieties had much larger variance of yard vs ecoroof plantings.


The shallots disappointed me, both on the ecoroofs and in the yard. Garlic wants its water to taper off in early summer, which is what makes it so well adapted to our climate of wet winter and dry summer; I had thought shallots share this preference. But looking over the literature, it seems shallots need water in the summer for best production; I provided them none. I want to keep the ecoroof largely irrigation free, so the shallots don't make sense there; in the future I'll plant them only in the yard, in easily irrigated areas.

Future Research

I feel very happy with garlic yields from the ecoroofs, so I don't see a need to grow any in the yard. We'll reserve the yard for more intensively managed crops, especially those benefiting from irrigation. That said, if we were staying here (instead of moving to Hawaii in a few months) and inclined to try the experiment again with better controls, I would:

  • Pre-pop cloves and allocate roughly equal sizes to the different planting patches.
  • Weed out the non polyculture plants.
  • Crop-rotate the yard patches, especially where they suffered root rot.
  • Plant yard and ecoroof garlic at the same time.
  • Plant yard test plots in full sun to match the ecoroof conditions.
  • Record scape harvests by variety and location to evaluate the full yield.
  • Use cloves from bulbs grown out for at least a year, to give us the opportunity to plant only the largest cloves of each variety. This would allow better comparison across varieties.
We would still have the variable of different polyculture companions in different patches, but otherwise the extraneous conditions would be much more uniform.

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