We just submitted a grant for putting ecoroofs onto our house, carport, and garage. I thought our conceptual approach and plant list may help other people contemplating ecoroofs, or those with thin soils for whatever reason. (Someone on the Portland Permaculture Guild list just asked about plants for a site with a few inches of soil over compacted gravel, so I sent her my plant list a
s a starting point.)
I selected the plants in the plant list below from books on ecoroofs, and from drought-tolerant plants listed in the Plants for a Future database and Martin Crawford's Ground Covers booklet. Many of the drought tolerant plants may survive drought by sending down deep roots, which won't work on the ecoroof, so many of my selections may fail.
Our grant proposal "Planting Plan" follows:
We consider the ecoroofs "Zone 2", a permaculture concept referring to areas accessed once or twice a week (as opposed to "Zone 1" areas of daily access where you would grow salad greens and so on). We'll grow crops which require relatively infrequent maintenance and harvest. Suitable crops include bulbs and other root crops, medicinals and herbs harvested for drying or other storage techniques, berries, and seeds for eating or animal fodder.
In our yard, we're experimenting with polycultures of perennial vegetables, trying to include nutrient accumulators, nitrogen fixers, beneficial insect attractors, aromatic pest confusers, ground covers, tall clumpers, and vines in patches through the entire garden. Given the limited species pallette for the ecoroof and given that we know even less about species interactions on an ecoroof than on the ground, we'll start with experimentation with simple polycultures of two plants at a time. Generally we'll aim to have a solid mat of low growing ground covers with taller clumping plants growing up through them. We'll try different plants in different combinations, and try different plants in different microclimates of aspect, soil moisture, and shade availability. As we learn what works well together and as plants volunteer themselves in new areas, we'll evolve more complex polycultures of more than two species.
We will design for year-round plant growth on the ecoroofs. In some places we'll use evergreen species, and in others we'll use two rounds of plants, for warm season growth and then for cool season/winter growth. In our regular garden we fill the winter niche with a combination of food crops of garlic and other Alliums, cover crops of fava beans and others, and self-seeding volunteers (such as the salad greens Montia sp, Barbarea verna, popweed [Cardamine unknown], Lapsana communis, and Lamium purpureum).
On the ecoroof we'll focus the winter crop on garlic, multiplier onions, shallots, and other Alliums which can grow over the winter and produce bulbs for later harvest. We'll also try some chard and kale, and maybe other greens to allow for a once or twice a week visit to the roof to harvest a salad or a bowl of cooking greens at a time. This seems the most efficient way to supplement our normal daily-use winter garden on the ground.
Spring Into Summer
Many "spring ephemeral" bulbs native to the West should work well on the ecoroof. Others have already reported that Camassia grows well on ecoroofs. We'll also experiment with the edible bulb producing genuses Triteleia, Brodiaea, Dichelostemma, Fritillaria, Scilla, and Muscari, many or all of which contain species of similar life cycle to Camassia: leafing out in early spring and dying back with the onset of our summer droughts. These should provide calorie rich bulbs without requiring additional irrigation. We can harvest these as soon as they go dormant, or wait til the fall or winter.
We will also experiment, especially in early years while we wait for the ecoroof to fully fill in, with growing baby carrots and perhaps other "baby" annual roots, taking advantage of the prime spring growing season before the ecoroof gets baked in the summer.
Summer and Fall
The ground covers should persist through summer and fall. In places where our spring ephemeral bulbs have died back, ground covers may be the only plants growing. In other places we'll have taller plants which also persist into fall.
Fall Into Winter
We'll plant our garlic and other Alliums, and sow seeds. Seed sowing will work best in conjunction with harvest of root crops, disturbing the soil and setting back the ground covers enough to open niches for the seeds to utilize.
To save on plant costs, for many plants we'll purchase fewer starts than ultimately needed (especially of the quickly spreading ground covers), and propagate them from divisions, seeds, and bulb offsets once they establish. In the meantime, we'll plant more heavily with annual crops such as garlic, baby carrots, and maybe even some spring greens to use the open space and minimize its colonization by unwanted volunteers. This will also allow us to experiment with a large number of species to see which succeed and which fail; after the first year or two those which succeed will have proven themselves and begun offering propagation material to fill in the areas of plants which failed.
Potential Species Lists
(still a work in progress):
Ground Covers / Low Plants
- Rubus nepalensis
- R. tricolor
- R. hispidus
- R. illecebrosus
- R. irenaeus
- R. pentalobus
- Astragalus glycyphyllos (Milk vetch)
- Montia perfoliata (Miner's lettuce)
- Montia sibirica (Siberian miner's lettuce)
- Valerianella locusta (Corn salad)
- Cornus canadensis (Bunchberry)
- Lotus corniculatus (Prostrate bird's food trefoil, especially "Plena" low-growing variety)
- Sempervivum unknown (Hen and chicks)
- Thymus sp (T. praecox, T. x citriodorus, T. pulegioides, and others)
- Origanum vulgare (Creeping oregano)
- Campanula poscharskyana (Trailing bellflower)
- C. portenschlagiana (Adria bellflower)
- C. carpatica turbinata
- Ceanothus sp
- Achillea millefolium (Yarrow)
- Fragaria chiloensis (Beach strawberry)
- Vaccinium angustifolium (Lowbush blueberry)
- Vaccinium pensylvanicum (Lowbush blueberry)
- Vaccinium vitis-idaea (Lingonberry)
- Vinca major
- Vinca minor
- Stachys affinis (Chinese artichoke)
- Arctostaphylos uva-ursi
- Berberis wilsoniae
- Mahonia repens (Creeping Oregon grape)
- Myrteola mummularia
- Taxus baccata (English Yew, "Repandens" or other low growing ground cover variety)
- Prunus tenela (Dwarf Russian almond)
- Ribes alpinum (Alpine currant)
- Astragalus crassicarpus (Ground plum)
- A. membranaceous (huang-qi)
- Agastache rugosa (Korean mint)
- A. foeniculum (Anise hyssop)
- maybe other Agastache sp.
- Melissa officinalis (Lemon balm)
- Hemerocallis sp (Daylilies)
- Garlic/shallots/multiplier onions
- Allium cernuum (Nodding onion)
- A. tuberosum (Garlic chives)
- A. schoenoprasum (Chives)
- A. moly (Golden garlic)
- A. acuminatum (Hooker's onion)
- A. senescens (German garlic)
- Tulbaghia violacea (Society garlic)
- Psoralea esculenta (Indian breadroot)
- Sedum spectabile
- Sedum telephium
- Linum perenne (Perennial flax)
- Salvia officinalis (Sage)
- Lavandula angustifolia (Lavendar, perhaps "Hidcote Superior" variety)
- Rosmarinus officinalis (Rosemary, preferably a dwarf variety)
- Berberis buxifolia "Nana"
- Amaranthus sp.
- Chenopodium sp.
- Trigonella foenum-graecum (Fenugreek)
Spring Ephemeral Bulbs
- Cammassia sp (quamash, cusickii, leichtlinii)
- Triteleia sp
- Brodiaea sp.
- Dichelostemma sp.
- Scilla sp.
- Muscari sp.
Hippie Grass Areas
(hang-out space and paths):
- Bellis perennis (Daisy)
- Achillea millefolium (Yarrow)
- Trifolium sp. (clovers)
- Lotus corniculatus (Bird's food trefoil, especially "Plena" low-growing variety)
- Chaemaemelum nobile (Chamomile)