our gardens after we’re gone

Ever won­der what your gar­den would look like if the human care­tak­ers just vanished?

Maybe I’ve been inspired by all the dis­as­ter flicks like 2012 or the His­tory Channel’s Life After Peo­ple series. But envi­sion­ing gar­dens after gar­den­ers is an inter­est­ing intel­lec­tual exer­cise that might help us answer that pesky ques­tion: What is a garden?

Would all the inva­sive species take over? Would the native plants reclaim their turf? For how long would you still be able to tell that a gar­den existed in a spot in the first place?

I looked at parts of my back yard and tried to imag­ine what would happen.

Within the first month, in South­ern California’s dry cli­mate, most of the pot­ted plants would per­ish for lack of water. Some of the suc­cu­lents might hang on longer, but with­out an exten­sive root sys­tem in the ground, they’d be doomed.

This lit­tle frog would be star­ing at a bog gar­den where all the bog plants have died back, once again for lack of water.

Within two or three months the fish­ponds would be dry: no waterlilies, no cat­tails, no sedges, no water for the local birds.

This pathetic patch of grass would go through boom and bust cycles, turn­ing green with the rains, dying back to brown other times of year. Seeds of other plants bet­ter adapted to the con­di­tions would even­tu­ally take hold. Maybe some plants from the local canyon. Maybe some hardy exotic or inva­sive species.

Behind the back fence of the house is this slope dom­i­nated by ram­pant ice­plant. The the neigh­bor behind me and I haven’t been able agree on what to do with the space. I’ve planted a small col­lec­tion of native plants to help sta­bi­lize the slope. These are species that with only once excep­tion can be found within a five mile radius of the house, and include plants like this night­shade, Solanum parishii…

…and Del Mar Man­zanita, Arc­tostaphy­los glan­du­losa ssp. cras­si­fo­lia, an extremely rare plant that’s on the Fed­eral endan­gered species list. The neigh­bor, how­ever, loves their ice­plant and can’t imag­ine of a slope with­out this gaw­daw­ful inva­sive species clam­or­ing all over it. The local chap­ter of the Cal­i­for­nia Native Plant Soci­ety has pre­pared a great pam­phlet on get­ting rid of ice­plant that you can view [ here ]. It goes into some great rea­sons to get rid of the stuff:

Planted on hill­sides of thou­sands of homes in San Diego, it has since crawled off the orig­i­nal site and into neigh­bor­ing Open Space parks, endan­ger­ing unique plants by smoth­er­ing them. Ice­plant pro­vides lit­tle habi­tat value com­pared to the plant com­mu­nity that it is replac­ing. Com­pared to the native shrubs, ice­plant has very shal­low roots that do not hold soil well; close inspec­tion often reveals gul­lies under­neath the twisted mat of vines. After rain, Ice­plant engorges with water, sub­stan­tially increas­ing its weight. As a result, ice­plant can cause the dete­ri­o­ra­tion of steep hill­sides by encour­ag­ing slump­ing – poten­tially endan­ger­ing the house above.

For peo­ple in sub­ur­bia, “habi­tat value” might mean plants that har­bor scary wild ani­mals and bugs, so that’s not always the most com­pelling rea­son to go native. The fact that ice­plant might endan­ger their prop­erty val­ues could be more persuasive.

So, return­ing to my main topic, the ice­plant would prob­a­bly over­run most of the native plants in a very few years and form a deep pile. Once we neglected the slope for a few years and found that the mat of ice­plant was start­ing to push the back fence over. Within ten years the fence would begin to fail and the ice­plant would begin its descent into the lower garden.

These plants along the back fence would stand a chance of sur­viv­ing with­out water. The yucca, palm, pro­tea would be tall enough to sur­vive an onslaught of maraud­ing ice­plant from behind. They’re plants that don’t require much main­te­nance, and this wall of foliage would prob­a­bly look unchanged for a num­ber of years. But the lower aloes and other suc­cu­lents would likely be smoth­ered by the iceplant.

This apri­cot against the back fence never looks great with­out sum­mer water­ing, but it sur­vives. It’s tall enough that it would prob­a­bly sur­vive the ice­plant inva­sion. Some of the adja­cent native plants do great with the nat­ural con­di­tions. They might not cope so well with the maraud­ing iceplant.

The neigh­bor on the side has Alger­ian ivy that requires con­stant clip­ping to keep it next door. Within two years it would begin to estab­lish itself in the back yard. Taller plants that might sur­vive the ice­plant inva­sion might have ivy crawl­ing up and smoth­er­ing them.

This raised bed near the house is where veg­gies and irri­gated plants live. Most of the exotic plants wouldn’t make it with­out water. The Dr. Hurd man­zanita, the bougainvil­lea vine and maybe the Gar­rya ellip­tica would prob­a­bly hang in there, how­ever, maybe for decades, maybe for much longer.

Fifty to seventy-five years out the house would start to fail. Plants might begin to move in. The sur­round­ing gar­den space would be over­grown with the hardi­est drought-adapted species. I almost never plant in rows, but the mixed ori­gins of the species–South Africa, South Amer­ica, Europe, as well as from all over Cal­i­for­nia, not just local species–would clue an inves­ti­ga­tor into the fact that a gar­den existed on the site. The rela­tion­ships between the plants would be dic­tated by nature, not a gar­dener pre­serv­ing order between plants with mis­matched lev­els of vigor.

Chances are excel­lent that one hun­dred years out, maybe two hun­dred or more, the most per­sis­tent inva­sive species would still be here. Ice­plant and ivy, plus fen­nel and black mus­tard that have invaded the local canyons, would fea­ture in the neigh­bor­hood land­scape. But while many inva­sives bask in the newly dis­turbed earth of a gar­den or the re-engineered grades around roads, they don’t always do so well long-term. Biol­o­gists have sug­gested that many native plants would return to a place where they’re not being pulled out or con­stantly mowed. My yard might be col­o­nized by the local Mex­i­can elder­berry, or toyon, or lemon­ade berry, or prickly pear. And maybe some of the plants I’ve already intro­duced to the yard will per­sist and repro­duce. The restora­tion of nature might spread from my house and from the wild edges of nature just a few houses away.

Even after nature returns, the occa­sional hardy exotic plant sur­viv­ing amidst the natives, along with some of the neighborhood’s plant­i­ngs of trees and shrubs in rows will make it obvi­ous: There used to be gar­dens here.

February 02 2010 | Categories: gardening • landscape | Tags: • • • | 26 Comments »