by Yvette Henson
Earlier this year, March 22, I wrote an article for this
blog about season extension and our High Altitude Season Extension research
trials in the San Miguel Basin (San Miguel and West Montrose Counties in SW
In that article, I said I
would post a follow up article about the different crops we have grown under
covers and how they have performed.
is that article.
We have been conducting season extension trials since
2011. Our raised bed trial beds are
located in Telluride at 8750’ elevation.
Telluride has about a 60 day frost-free growing season from mid to late
June till the end of August/early September. In the previous blog post I gave a
summary of what we have learned about growing under the different season
extension covers that we chose and best uses for each cover based on how crops
perform grown under them.
The materials we chose for our covers are (left to right, in
the above photo): Agribon Ag30, a medium
weight (0.9 oz/yd2) spun-bonded polypropylene row cover fabric; Insulated 5mm
XP paneling, a flexible polyethylene cover,
fitted with an automatic vent opener;
Dio-Betalon (Tuffbell 3800N) polyvinyl alcohol film and no cover for our
control bed. Initially, we layered
Dio-Betalon and 30% Row Cover but eventually we added another bed and separated
the two layers.
In 2011-2012, 2012-2013 and 2014-2015 we grew different
greens ‘through’ the winter. Eagle
County and Teller County collaborated in the first two seasons by growing the
same things along with us. We trialed
several different varieties of spinach (Spinacia
oleracea), kale (Brassica napus),
lamb’s lettuce (Valerianella locusta)
and arugula (Eruca sativa). In 2011, we planted in mid-September, got a very
small harvest before the holidays and then started harvesting again in late
February or early March. We learned that
mid-August is the better planting time because the plants get more time to
establish and we get a better pre-holiday harvest. All the greens did best under the Solexx
cover followed closely by the 30% Row Cover + Dio-betalon layered. Kale didn’t overwinter well. Spinach and arugula produced the most with
only some winter damage. The lamb’s
lettuce was the hardiest green and the earliest to mature. It was also the only green that didn’t seem
to be affected by day length and temperature. The other greens would stop growing when the days were the shortest and
coldest and would resume growing when days began to get longer in late February.
2012-2014 we grew 7 replications of many different lettuce (Lactuca sativa
) varieties at 3
The first year we planted seed
in mid-May but by the 3rd
year we had started even earlier – by the
week in April.
succession planting (2 weeks apart) and overwintering. Overall, 30% Row Cover +
Dio-Betalon layered together gave the highest yield but Dio-Betalon alone gave
the best quality.
planting worked really well and give a longer season of head lettuce rather
than a single large harvest.
that the lettuce needed to be about half way mature to overwinter well.
Lettuce loves growing in the mountains!
If you aren’t growing head lettuce give it a
try next season.
In 2015 we grew 4 varieties of Open Pollinated carrots (Daucus carota
We direct seeded
mid-March and harvested mid-June.
could have harvested earlier.
We got the
best yield and quality of carrots grown under Dio-Betalon, followed by 30% Row
Both of those covers get better
light transmission and don’t get as hot as our Solexx bed.
So, it makes sense that carrots wouldn’t grow
as well under Solexx since carrots are cool season crops.
An interesting fact about one of the carrot
varieties we grew is that ‘Pusa Asita’ carrots are a short day variety that
does well in the cool season of hotter climates.
Short season carrots don’t do well in the
2016, we grew 3 varieties of Open Pollinated broccoli (Brassica oleracea var. italica). We chose varieties that would produce both
heads and side shoots to extend the harvest.
We started the plants from seed and grew them out to seedling stage
before we planted them out in mid to late May.
Like carrots, broccoli is a cool season crop so it grew better under the
more ventilated covers. The Dio-Betalon
cover produced the earliest and highest yield of heads and the 30% Row Cover
produced the highest yield of shoots. We
found we preferred to eat the side shoots rather than the heads—they were
tenderer. Broccoli grows fine with no
cover, in fact no cover produced better yield than the Solexx cover. However, covers give the advantage of an earlier
harvest and protection from cabbage worms, etc.
In 2017 we grew 3 varieties of
bush green beans (Phaseolus vulgaris)
We also grew a short trial of bush green
beans in 2011 and a full trial in 2013, along with summer squash.
The results of the 2017 bush bean trials
compared to the 2 earlier trials was so different and we are still trying to
figure it out.
But in a nutshell, bush
beans grow much, much better under cover than with no cover!
They are warm season crops so the additional
heat that some type of cover provides is definitely needed to grow them in the
This year we are growing 3 varieties of day-neutral
strawberries (Fragaria × ananassa).
has been a challenging year to try to establish strawberries because of the
drought we are experiencing.
We will continue
this trial in 2019 after we overwinter the plants under covers.
To summarize and remind you of what I wrote in the March
article, growing under cover compared to growing in the open without cover improves
the growth and yield of most crops and gives protection against insects, wind
and harsh sunlight.
For the warm-season
crops we’ve grown (beans, summer squash) most have performed best under Solexx
and Dio-Betalon or 30% Row Cover + Dio-Betalon layered.
Cool-season crops (winter greens, lettuces,
carrots and broccoli) haven’t done as well under Solexx as the other covers.
Sometimes they even grow better under no
cover than under Solexx!
has yielded earliest cool-season crops making it a good choice to get extra
early harvest before it gets too hot in the summer.
It is also better at holding moisture in the
soil than the other covers but the humid environment can contribute to disease.
Solexx also tends to get salt buildup in the
soil because it doesn’t allow any rainfall through to leach it out.
The Dio-Betalon cover gives early and good
yields of all crops and so is a good choice for both warm season and cool
Dio-Betalon lets in a lot of
light and has produced good quality crops, especially colored lettuces.
We’ve found the soil under this cover can dry
Cool-season crops do very
well grown under the 30% row cover fabric.
It creates a humid environment, the lushest vegetative growth and helps
with seed germination.
moist environment also promotes disease.
Dio-Betalon + 30% Row Cover layered increases the benefits as well as
the drawbacks of either cover used alone.
Both together let in less light.
We don’t grow under both layers anymore.
For some cool season crops planted at the recommended time (not extra
early) the only benefit of covers is insect and critter control, shade and wind
I’ll be glad to answer any questions you may have about
growing under cover and/or the varieties we have grown. Contact me at Yvette.Henson@colostate.edu