What are the best groundcover species?

In my mind, the ideal groundcover would prevent any unwanted seeds from making contact with the soil, would draw in and seal in all moisture from precipitation, and would have entirely undemanding roots that offer no competition or inhibition to whatever else I have intentionally planted. Any additional benefits such as soil building (e.g. clover) or edible parts are nice but are not part of the core mission.

Of course we don't live in a perfect world, and nothing is going to live up to those high standards, but I'd love to hear about the plants that come closest in your experience.

Thanks.

Short answer: for annual vegetables, purslane. Possibly chickweed.

Long answer:

Mosses could also be possible. But they’re hard to cultivate.

I would say that a very good ground cover is tree leaves dropped from above. Especially big ones like maple, sycamore, oak, cottonwood, et cetera. Nut trees have good leaves for this: oak, hickory, chestnut especially. (Have you seen how enormous a good shagbark hickory leaf gets?)

In an established perennial ecosystem there should be no particular need for ground cover because the plants themselves cover the ground. Path plants are another question, and many of those come in on the basis of being well adapted to a particular situation.

If you can get ahold of large quantities of sawdust, that would also be quite excellent for your purposes. This is an input from elsewhere, but one that is considered a waste product. In my valley it is available in gigantic quantity from a factory—they have a big shed with a chute and all the sawdust goes down the chute, free for the taking, with shovels provided. There is nothing, nothing like sawdust mulch for holding water and trapping evaporation. The only issue is that it can bind up nitrogen if you’re not careful, which could be a good thing or a bad thing depending on where you put it. The worms will accept it as an open invitation to plough your soil with gusto.

If we look to natural ecosystems, we can see that the most persistent perennials (trees) get to be the tallest, and then there are herbaceous perennials at their feet. Between the herbaceous perennials are ground covers, typically in sparse quantities. If the ecosystem has regular disturbance from drought, grazing, mowing, stagnant water, cold, etc., then these ground covers become stronger, because they are ground hugging, they escape from the harshness by being small. Mosses, lichens, low herbs and creeping plants inhabit the droughty ridges and boulders where nothing else can make its home. Then new seeds come in and, in the more nurturing environment created by these plants, brambles and gooseberries, birches, maples, young trees are able to establish. So the ground covers are only tending to be naturally dominant in ecosystems characterised by environmental harshness or persistent disturbance that does not let taller perennials become dominant, which would shade them out.

What a ground cover means when you are growing annual veggies is one thing; perennials, another; and trees, yet another still.

So… most of these ground covers, the perennial ones at least—like clover or ground ivy—are a successional stage up from the majority of common annual vegetables, and are likely to outcompete them and prevent their germination and growth in my experience. Not purslane, though. Strong, deep-rooted perennial species can survive in the midst of perennial ground cover species, and if left to their own will overtop and partially shade them out. And trees can deal with a gardener’s nightmare ground cover, like ground elder/bishopweed/goutweed or carpet bugle.

 I like  creeping charlie, because it is easy to remove if necessary.
I haven't been able to transplant it, much less cultivate it.
I sow diakon radishes under tomatoes plants and the like.
The seed is cheap, the leaves shade out weed seeds, they grow quickly and they taste great.

I think perennial peanuts could be great as ground cover, but not in colder climates.

Strawberries, especially the wilder varieties like the alpine ones could be ideal ground over.

Edward Finch wrote:In my mind, the ideal groundcover would prevent any unwanted seeds from making contact with the soil, would draw in and seal in all moisture from precipitation, and would have entirely undemanding roots that offer no competition or inhibition to whatever else I have intentionally planted. Any additional benefits such as soil building (e.g. clover) or edible parts are nice but are not part of the core mission.

Of course we don't live in a perfect world, and nothing is going to live up to those high standards, but I'd love to hear about the plants that come closest in your experience.

Thanks.

What's the end goal? Is it just ground cover? If so then single species is not really the best idea. Mix it up, variety almost always works best!

In my opinion, ground cover will not prevent unwanted seed from germinating, Only a pre-emergent like corn gluten will do this.

I have always used Ajuga as a ground cover though I could recommend strawberries.  I also like pennywort:

https://permies.com/t/68485/Plant-ID-Creeping-Charlie

How tall a plant do you want?

I planted mint in a hugel berm about 5 years ago. Originally I did this to combat ants which were taking over a large section of the newly built berm. Ants communicate thru scent so the mint made them disappear in less than a week.

However, the mint ended up spreading all over the berm. At first I thought this would be a problem but it definitely wasn't. There's haskap, raspberry, gooseberry, currant and various veggies growing side by side with the mint. I rarely have to weed and also the grasshoppers seem to avoid the mint.

I'm going to throw in another vote for Creeping Charlie, also known as Ground Ivy.

The main reason I appreciate the plant is that it will grow in places that other ground cover struggles to establish in. I've seen it grow over wood chips, chicken litter, rocks, and other bare soils. It is a gradual growing cover that stays established towards the surface of the soil. If it starts to grow into areas that I prefer it not to be, I simply rake it back and roll it into a log of sorts.

I liken it to a natural erosion blanket for hillsides and slopes.

There is another plant, Purple Dead Nettle (Lamium purpureum) that I used to confuse with creeping charlie.
I believe Shawn from Edible Acres has had some good experiences with it as a ground cover in vegetable beds.

I really like strawberries as groundcover!

Weeds have grown through the wood chips in sections of my garden pathway, and my favorite area is filled with dandelion, cat's ear, and other dandelion lookalikes. The rosettes hug the ground year-round, preventing most other weeds from getting a foothold, and they're not invasive. It's also noticeably a bit cooler in this section mid-summer, as the leaves keep the ground cool and moist underneath. And it takes awhile for the flowers to get tall enough or thick enough to need cutting. They get a bad rap as a "weedy" groundcover, but they check off most of my boxes.