The best cover crop for a shady understory

I'm living in a tiny home, and have began creating a landscape around it with summer cooling in mind. I've planted a number of shrubs and trees including plums (for food) and lilac (for shade and cooling). Beneath them are various flowers, clover, stinging nettle, siberian pea shrub, hawthorn, and native snowberries. This is being planned to create a "jungle" of plants all competing for the same light and creating dense shade and a pocket of cool, moist air around the structure during summer time. I'd like to make a ground cover at the very bottom layer, beneath everything else( even things such as mint that don't let much light through), in order to increase humidity and decrease temperatures within the "jungle" on the South facing wall. An aquatic plant that tends to slurp up extra water out of the soil would be ideal. It should be a ground cover that is readily available, preferably as seeds (I can't afford to buy a bunch of potted plants), and can tolerate extremely low light conditions. Any suggestions would be appreciated, thanks.

I recommend New Zealand spinach. It tolerates both heat and cold and produces abundant seed along the vie at each leaf. The leaves are very desirable to eat when growing in the shade but in bright sun the leaves are small tough and close together.  The north half of my greenhouse is in  shade of the roof in the summer and the temperature in there is over 90 when the sun shines. I take my container plants out of there in the summer and the New Zealand spinach takes over the space and produces unabundant crop in the heat but also survives when the temperature drops to 30 in the winter.

Hans Quistorff wrote:I recommend New Zealand spinach. It tolerates both heat and cold and produces abundant seed along the vie at each leaf. The leaves are very desirable to eat when growing in the shade but in bright sun the leaves are small tough and close together.  The north half of my greenhouse is in  shade of the roof in the summer and the temperature in there is over 90 when the sun shines. I take my container plants out of there in the summer and the New Zealand spinach takes over the space and produces unabundant crop in the heat but also survives when the temperature drops to 30 in the winter.

It can occasionally get down to 20F here during winter, and overnight frost is a regular occurrence. Any chance it might survive winter with enough shelter from other plants? Oregon grape can form a dense canopy and won't lose its leaves during winter.

New Zealand spinach will return from seed if frost killed. Oregon grape and Washington holly a taller variety are excellent choices. Salal (Gaulthoria shallon) is an evergreen plant with glossy, waxy foliage that remains beautiful year round. Fuzzy, white or pink bell-shaped flowers droop from the plant in spring, soon to be replaced by bluish-black berries.
The bland sweet berries are a good complement to the sour berries of the Washington holly and Oregon grape.
Read more at Gardening Know How: Salal Plant Info: Tips On Growing Salal Plants https://www.gardeningknowhow.com/ornamental/flowers/salal/growing-salal-plants.htm

What about Creeping Dogwood?  https://www.gardeningknowhow.com/ornamental/groundcover/bunchberry-dogwood/growing-bunchberry-dogwood.htm

It looks like it stays lower than Salal or Oregon Grape and makes a very solid groundcover.  I've been thinking of planting it on the north side of my cabin, which has very limited light and an annoying bit of grass to mow.

Morfydd St. Clair wrote:What about Creeping Dogwood?  https://www.gardeningknowhow.com/ornamental/groundcover/bunchberry-dogwood/growing-bunchberry-dogwood.htm

It looks like it stays lower than Salal or Oregon Grape and makes a very solid groundcover.  I've been thinking of planting it on the north side of my cabin, which has very limited light and an annoying bit of grass to mow.

I have seen it in its native habitat but requires a constant wet soil like in a forest canyon. In a situation with summer drought and no irrigation it would not do well.

Nathan Watson wrote:I'm living in a tiny home, and have began creating a landscape around it with summer cooling in mind. I've planted a number of shrubs and trees including plums (for food) and lilac (for shade and cooling). Beneath them are various flowers, clover, stinging nettle, siberian pea shrub, hawthorn, and native snowberries. This is being planned to create a "jungle" of plants all competing for the same light and creating dense shade and a pocket of cool, moist air around the structure during summer time. I'd like to make a ground cover at the very bottom layer, beneath everything else( even things such as mint that don't let much light through), in order to increase humidity and decrease temperatures within the "jungle" on the South facing wall. An aquatic plant that tends to slurp up extra water out of the soil would be ideal. It should be a ground cover that is readily available, preferably as seeds (I can't afford to buy a bunch of potted plants), and can tolerate extremely low light conditions. Any suggestions would be appreciated, thanks.

Reading the answers, I realized I was somewhat vague in the requirements and habitat of this ground cover. I envision this strip of dense vegetation around my tiny home to function like a tropical rainforest. In a tropical rainforest, the air below the canopy is always cool and moist because there is so much lush plant life. And the reason the plants grow so well is because of all the humidity and moisture everywhere.

This ground cover will be in a place that will stay moist most of the time due to all the lush vegetation above it. On a long term basis, I intend to water it only every 1 to 2 weeks during summer, but will water it far more often than that while it's getting all established. Ideally it would be a ground cover only a few inches tall, to allow another layer such as mint to grow above it.

This ground cover plant should survive in very low light conditions.

I live in a zone 8, but with some evergreen shelter plants above, it might be more like a zone 9 at the ground cover layer. The ground cover layer would preferably be a perennial in this environment, but an annual that can seed and reproduce in very low light conditions would also work.

Morfydd St. Clair wrote:What about Creeping Dogwood?  https://www.gardeningknowhow.com/ornamental/groundcover/bunchberry-dogwood/growing-bunchberry-dogwood.htm

It looks like it stays lower than Salal or Oregon Grape and makes a very solid groundcover.  I've been thinking of planting it on the north side of my cabin, which has very limited light and an annoying bit of grass to mow.

I did some research and found that " No fruit was produced by any understory species in areas where solar transmissivity was 3% or less". Apparently some species within the Cornus genus can at least survive on as little as 3% sunlight. It's unclear whether this applies to Cornus Canadensis (Bunchberry Dogwood), but it sounds like it's an incredibly shade tolerant plant. (source https://www.fs.fed.us/database/feis/plants/forb/corcan/all.html )

This is perfect for a ground cover. Thanks!

There is still room on the ground cover for some variety if anyone has any other suggestions for ground covers that might also work.