I live where the plant-eating critters
abound and I don’t have a fence, so I’ve been relegated to using pots on my second-story
deck. We mountain gardeners have to be resilient and creative, and each year I
keep trying new techniques to improve the performance of my potted plants.
Since my first frost date is approaching I’ve started evaluating this year’s
strategies and I have some thoughts I’d like to share.
Last year’s experiment
Moisture management is a big issue in our
semi-arid climate and it is especially critical with container gardening. Last
year, in every pot I used a plastic insert to hold the soil inside each
decorative outer pot (see photo). I also put rock mulch (I used 1/2” gravel
from my driveway, and washed it) on top of the potting mix in each pot. I found
I had to water only one time per week, even during our hottest and driest
spells.
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| Decorative outer pot contains a plastic insert |
This year, I tried a mixture of techniques
since I only had a few plastic inserts and I had a bunch of new lovely
pots.
The potting mix
One strategy was to increase the
moisture-holding capacity of the potting mix itself. Most potting mixes are
formulated to improve drainage and aeration. They often contain a lot of peat
and they can dry out quickly. For soils in the ground, we are taught that
compost increases the moisture-holding capacity of porous soils, so I applied
that concept to my pots. I added extra compost to my potting mix in an attempt
to improve the moisture-holding capacity of the mix. To ensure good drainage,
so I also added perlite (the little white balls that you see in most
potting mixes, they look like styrofoam). (1.5 cu ft bag potting mix + 1.5
cu ft bag compost + 8 qt bag perlite, mixed well in a wheel barrow)
I believe the compost improved the
moisture-holding capacity of the soil. However, I did not fill any of my pots
with un-amended potting mix, so I had nothing to compare to. Maybe next year I’ll
do a side by side comparison, so I know for sure.
Good drainage
While it’s important to retain moisture in
our dry climate, we also can have torrential downpours and I know people whose
potted plants have drowned, so I also wanted to provide good drainage. As I
mentioned above, I made sure to add extra perlite to my amended potting mix. I
also made sure every one of my pots had ample holes in the bottom. And to be
sure the holes drained freely, I raised the pots off the deck by using 1/2”
wooden blocks (see photo). During our wet spell early in the season, I didn’t
lose any plants to drowning, so I consider this aspect to be a success. But
there’s always next year and whatever crazy weather it brings, so time will
tell.....
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| 1/2” wooden spacer elevates pot and keeps drain hole free of obstruction |
Self-watering containers
The most successful aspect of my
experiments this season involved the use of self-watering containers. I tried
several configurations and was pleased with all of them. I got inspiration for
DIY self-watering pots from an excellent book that a fellow Master Gardener,
Debbie of Gilpin County, brought to one of our classes: The Vegetable
Gardener’s Container Bible by Edward C Smith. I’m sorry I didn’t take
pictures while we were making the DIY versions, but you can get an idea of what
the reservoirs look like by doing an internet search for ‘self-watering
container reservoir.’ My key criterion was having a large reservoir for water.
I used a commercially pre-made
self-watering container (Earthbox) and compared it to a DIY version in a 10
gallon plastic tub (see photo). The commercial version has a reservoir that
holds 3 gallons of water to serve 15 gallons of soil mix and my DIY version was
a little smaller, but had a similar ratio of reservoir size to soil volume.
They both had plastic covering the top of the soil, so no water was lost
through evaporation. I have several tomato plants in them. They worked really
well and I found filling the reservoirs once a week to be adequate. I’ve gotten
my first fruit from my russian tomato plant and have lots more on the way!
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| DIY self-watering pot using a 10-gallon plastic tub |
Another comparison
I did another comparison between two larger
pots. One pot was filled only with soil mix and the other pot had a 1 gallon
DIY reservoir in the bottom half.
The large pot containing only potting mix
had some problems. I watered it regularly and faithfully until water ran out of
the bottom. But my plants (especially the basil and tiny ageratum) were
perpetually wilting. It took me awhile to realize that, even though I had been
watering frequently during the dry spell, part of the soil mix had completely
dried out and most of the water was running out of the pot instead of being
absorbed into the soil. So I embarked on a re-wetting program, watering in
small amounts many times per day until the soil mix was moist all the way
through. It’s a good thing that most of the plants in that container were
drought tolerant!
Without a doubt the self-watering pot had
superior performance. I still needed to water regularly from the top, because the
very top 2” of the soil dried out, but it was much more forgiving. My
moisture-loving canna and dahlia did very well and never wilted even
during the hottest, driest part of the season. The soil in the DIY
self-watering container never dried out completely.
Next year
So, with information from this year’s
experiments I have some ideas to use for next year’s pots. I loved the
self-watering containers and will expand my use of them. I think the use of
mulch is a good idea and I will incorporate it into my plans for next year. And
I would like to compare the moisture-holding capacity of plain potting mix
versus potting mix amended with compost and perlite.
As the first frost approaches I have some
consolation that next year’s pots will be even better than this year’s!
PS I got inspiration for the DIY
self-watering pots from an excellent book shown to me by a fellow Master
Gardener, Debbie of Gilpin County: The Vegetable Gardener’s Container Bible
by Edward C Smith. And further great advice on all aspects of container
gardening can be found in The Bountiful Container by McGee and
Stuckey.
Most importantly, the CSU website has great
information that helped me adapt to our regional conditions the information
that I found in the books. I particularly recommend:
Container
Gardens - Fact Sheet 7.238 (http://www.ext.colostate.edu/pubs/garden/07238.pdf
)
Climate Summaries by region in Colorado -
Garden Notes 740 (http://www.ext.colostate.edu/mg/gardennotes/740.html)
Container
Gardening (http://www.colostate.edu/Dept/CoopExt/4dmg/Plants/contgard.htm)
