The Largest Living Wall-a Year Later
by Mary Jasch
“It’s doing well,” says Lorrie Baird, senior gardener at Longwood. “There are a few plants that are being a little feisty with us, but overall it’s doing really well.”
The concept of the wall was created by British landscape architect Kim Wilkie and further designed and detailed by Philadelphia landscape architect Stuart Appel of wellsappel. Its 47,000 plants are subtropical and tropical, with the majority of them ferns.
No flowers bloom here on this tunnel of green profusion. Instead, sheer mass, naturally woven fluffy texture, variety of form and habit, and endless shades of green in prime condition create the attraction. Such is the Polypodium aureum Blue Star. Silvery-blue fronds on long petioles reach out from its position high on the wall. And only one plant is variegated: the Pteris fern.
For a plant to do well on the wall, they must never, ever have a lull. “We have to make sure that they’re looking good every single day of the year,” Baird says.
Asparagus fern has done well on the green wall, which completely covers both sides of a long hall with a vented glass top. The walls are composed of individually planted panels that easily pop out for close inspection, changing places with other panels of a different plant type, treatment or replacement.
Winter temperatures are a low of 50 degrees and a high of 70 degrees. At 70, the vents are opened. There is no air-conditioning so the vents are almost always open in summer. Shading begins with a light coat in March and heavier coats as temperatures warm. It’s removed in late October.
Asparagus fern thrive in the high light conditions of the wall and, with its tuberous roots tolerate drying out, so they do very well on the top of the wall. “The Victoria Bird’s Nest fern, Asplenium nidus ‘Victoria’, has done very well. It’s pretty too, so we like using that a lot.” Asplenium dimorphum ‘Austral Gem’ also flourishes.
But some plants are not too happy even when moved to another microhabitat with variances in lighting, temperature and nearness to the watering system.
Take Lemon Buttons Fern, Nephrolepis cordifolia 'Lemon Buttons'. “I think it’s going through a shedding period where it’s losing all its old growth and we just can’t have panels that are shedding all their leaves,” Baird says. “So we decided to take all those out and we’re replacing them with different ones.”
Maidenhair fern didn’t do well, beautiful in winter but yellowing in the heat of summer no matter what. Staff cut back the fronds but the plants never rebounded well. Most of the maidenhair has now been replaced with other species. “Again, we just can’t have empty panels that we cut back. We can’t wait for them to refresh. It’s a shame because it was so beautiful last year. Whenever the vents or a door opened, it had a lot of movement to it.”
Gardeners check the wall every day to make sure there are no pests or other problems with the plants and that the irrigation is working.
Irrigation lines run through the wall with light doses of fertilizer water, even in winter because the plants put on growth in this warm, sunny environment. Right now the fertilizer of choice is organic 10-4-3 Daniels Plant Food three times a week.
“We’ll keep fertilizing through winter because we run this as a hydroponic system and there’s no soil in the coconut core fibers. What we give the plants is the only nutrients they have available. Coconut fiber can’t hold on to many nutrients so maybe we’ll fertilize in winter two times a week just so it always has nutrients available.”
“Since it’s been installed we have not sprayed any synthetic pesticides on the green wall. We’ve used all beneficial insects.” Every two weeks upon IPM team inspection, packets of four or five species of beneficial insect eggs are attached to the wall. As the predatory insects hatch, they emerge and look for food – herbivorous insects.
“We are currently using parasitic wasps for aphids and whitefly, Minute Pirate bugs for thrips, predatory mites for spider mites, Swirskii mite for whitefly eggs, larvae, and larval thrips, and Mealybug destroyers for mealybugs.”
Sometimes a problem occurs with scale on spider plants. Beneficials don’t seem to find scale very appetizing so staff grooms the plants by hand. They remove infested leaves or remove scale with alcohol.
As the plants grow and panels become crowded, Baird and crew thin older foliage so newer foliage receives light – especially spider plants.
So what does the future hold?
The coconut core panels, predicted to last about 10 years, will eventually be replaced. Plant suppliers offer suggestions about new possibilities, but so far staff is pleased with the success of the majority of the current plants. “I hope they’ll live for 10 years. I hope we won’t have to change anything for 10 years,” says Baird.
So what has Baird learned about hydroponic walls in the past year?
“For me it’s been a huge science project and I love science so it’s been a big experiment to see how we can get these plants to grow their best. It’s taken us a good year to figure out the fertilizer schedule and it’ll change as the plants grow because as the wall ages it’s going to need more fertilizer and more water.”
There's no "save the earth" hype surrounding this green wall, although some Longwood reserchers are studying how plants, in general, clean the air at Drexel University.“But for our wall in particular, we’re not. We’re just using it as a way to show people about green walls and how they can grow them.
“I think everyone’s impressed by the wall. Visitors say the hallway has a very fresh smell to it because all the plants are cleaning the air in that area so I think everyone’s very happy.”
Longwood Gardens Green Wall:
-4,072 square feet
-3,590 planted panels
-28 plant species
-The plants provide same amount of oxygen as 90 14-foot trees
-32 weeks the plants grew at the nursery
-3 climate-controlled trucks transported the plants to Longwood
-3,900 linear feet of irrigation drip line
-24 irrigation zones
-2,520 man hours to install the wall
Longwood Gardens: www.longwoodgardens.org
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published November 23, 2011