Gardening the Garden

Question:

I have not seen a grass that will not grow in a container. However your best luck will be with smaller sized grasses one or two zones hardier than yours. Large sized grasses like Pampass and Ravenna will grow in pots but may not achieve the size necessary for blooms. Over wintering will be your main concern. The pots can be moved to a protected location in your garden with soil and shredded mulch around and over them. The soil should stay moist all winter. If you’re in a high rise with a balcony, the pots can be overwintered packed with insulating material like leaves, styro peanuts, etc inside large covered garbage cans. This of couse wlll be kinda hard to hide from the condo board…  

Response:

Second, a container gardening book I perused at my local bookstore (can’t remember the title, but it was oriented towards British gardening) noted that many ornamental grasses required roots twice as deep as the grasses which grow aboveground. Is this true? Does this mean that in order for grasses whichj potentially grow two feet necessitate a barrel that was four feet deep ?! (Or is this only true for select grasses — and if so, which ones?)

I grow 8 different genera of ornamental grasses and I have yet to encounter one that has roots that extend twice as deep as the top growth. I can say that roots of ornamental grasses which have been established for awhile can be massive and very dense, making transplanting or dividing a serious chore, but that deep? no. I grow several grasses in containers – my favorites are the carexes or sedges. They vary in hardiness according to the species, but most are hardy to zones 5 and 6, some even to zone 3. I have also found that the larger the container, the less likely it and the plants in it will be damaged by cold. Pam – gardengal PNW zone 8

Response:

– Hide quoted text — Show quoted text – Second, a container gardening book I perused at my local bookstore (can’t remember the title, but it was oriented towards British gardening) noted that many ornamental grasses required roots twice as deep as the grasses which grow aboveground. Is this true? Does this mean that in order for grasses whichj potentially grow two feet necessitate a barrel that was four feet deep ?! (Or is this only true for select grasses — and if so, which ones?) I grow 8 different genera of ornamental grasses and I have yet to encounter one that has roots that extend twice as deep as the top growth. I can say that roots of ornamental grasses which have been established for awhile can be massive and very dense, making transplanting or dividing a serious chore, but that deep? no. I grow several grasses in containers – my favorites are the carexes or sedges. They vary in hardiness according to the species, but most are hardy to zones 5 and 6, some even to zone 3. I have also found that the larger the container, the less likely it and the plants in it will be damaged by cold.

As I understand it, the problem with otherwise hardy plants in containers in the colder zones is not the cold itself but rather midwinter thaws.  Such a thaw can trick the plants into believing it is Spring, causing them to break dormancy and leave them vulnerable when the cold returns. When plants are in the ground, a thaw must be quite sustained before there is any significant effect at the root zone.  However, when they are in containers, the soil thaws not only from the top but also from the sides and, if the container is on a masonry (or other heat collecting) surface, from the bottom. What I did when I was growing perennials in containers was to simply insulate the pots and overwinter them in a shady place where snow tended to accumulate. By doing this I was able in zone 5b to successfully overwinter in containers hosta, clematis, heuchera, astilble, lily-of-the-valley and euonymus shrubs. While I agree with Pam that the larger the container, the larger the soil mass and the slower it is to thaw, some of the containers I was using were as small as 12". — Jim Voege

Response:

First, I read in Ken Druse’s "New York City Gardener" that outdoor container plants freeze more easily since the containers are above ground, so I should pick plants that are a zone or two lower than the zone I’m actually in. I’ve always thought that NYC was in Zone 6, but Druse says it’s in Zone 7 — which is it really?

It depends where you are in the city.  The majority of NYC is in zone 6, but there are a lot of microclimates across the five boroughs.  I always planted everything hardy to zone 5 — I think it’s a good idea to plant down a zone no matter where you are, since this will insure against the oddball nasty winter that’s sure to come along.  And, it helps container plants, which do indeed freeze. Should I look for grasses suitable for Zone 4 to be safe? (I just ordered umn.edu’s "Ornamental Grasses For Cold Climates [$7.50] just to be safe.)

Good book, and the planting down can’t hurt. I’m not an expert on grasses, but there might also be something for a far higher zone that you would be able to bring inside for the winter. — Jessie ex-PA (z.7), ex-NYC (z.6), now MN (z.4, brrrrr!) entwold at att dot net "Thoreau never mentioned the icky little bugs." – City Boy

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