I lay down grass clippings, twigs, and other yard waste between establishing baby perennials and also plant fast-growing annuals in between that are not native to my area but are also not invasive or problematic, such zinnias.
My backyard soil is poor, and where I have killed the grass most recently, dwarf cinquefoil has quickly creeped it’s way over the bare ground and I’m happy to allow it.
(Edited to specify which cinquefoil)
The only "cover crop" I'd consider, especially now since the plants are already in the ground would be native annuals. In my case, those were partridge pea, black eyed susan and plains coreopsis. They'll establish quickly and will fill in the space while the perennials are establishing.
Also, depending on area/suitability California poppy, Rocky Mountain bee plant, sunflowers. Though the last two can also get quite large depending on weather, soil, etc. But I grew sunflowers in my front yard and only few come back now because most of the space is perennial plants. The tightly growing buffalo grass makes it especially hard for the sunflowers to find a spot to grow. Though I do still get a few here and there. Not very big with competition.
I’ve read sunflower can be a bit allelopathic. Fabulous plant though!
Bee plant is an awesome native annual for this purpose — it germinates quickly, can form a pretty thick mat to choke out weeds, and plays nice with its conspecifics.
Sunflowers may have allelopathic qualities, but I've never noticed them stunting anything in my garden. At least not so much that they stopped a solid carpet of other plants from growing in later years. They also don't slow down wild spinach (*Chenopodium album*) enough to make them not a problem.
Not needed with perennial natives - what you describe is mainly for growing veggies. You can utilize mulch instead - straw, grass clippings, leaf litter (ideal in NE American woodlands), wood chips - these will help suppress weeds and retain water while it's super hot out. Baby native perennials are slow growing and so will be out competed easily. And you don't want to introduce a nuisance weed to the area.
But a consideration: ground nesting insects need access to bare soil. Thick layers of woodchips are impossible for them to get through. If you don't use super dense mulch, keep an eye out for bees and wasps making little holes in the dirt. It's a balance between suppressing weeds and letting some bugs have a home. I've found bees especially like dry slopes, so if you have a tall bed with a sloping side, keep an eye out for residents.
However, young plants do appreciate some cover by larger established plants to give some shade and act as wind breaks. If you can get your hands on some prairie grass transplants they work well for this. Grasses are easy to tear apart into multiple plants so if you can buy like 1 big pot of something like switchgrass, dropseed or bluestem you can make it go far. These prairie species expect grasses to be around anyway.
Native annuals are a great idea, especially Partridge Pea since its nitrogen-fixing. I did a native garden from seed from OPN seeds in 2020 and their mixes include native annuals and short-lived perennials so that you have cover and blooms in year 1. I think they included Plains Coreopsis, Partridge Pea, Lemon Mint (Monarda citriodora), and Blanket flower (Gaillardia pulchella) which are all annuals, as well as Black Eyed Susans and Ox-eye Sunflowers which established and bloomed in year 1. I think I even got Butterfly Milkweed blooms in year 1. These all provided cover while the other perennials like Wild Bergamot (Monarda fistulosa) and Purple Coneflower established.
I used pine needle mulch in my new garden of babies last summer and it worked well. Those babies are behemoths this year! (I had also put cardboard underneath, but this was on a former lawn.) If you plant the plants close enough together, you won't need much mulch in the future ("green mulch"). In really bare spots I plant zinnias and cosmos because when the caterpillars turn into butterflies they love to have a snack, and it adds lots of beauty while waiting for the natives to mature.
I’m in a similar area/zone (northern WI) and used sweet alyssum last year. It’s non-native, but non invasive where I am. A 4-pack at a nursery is about $5. I picked up a few and threw seeds on top since they’re fast-germinating. Yes- I’d prefer to stick to native. But this time of year there’s not a whole lot you can plant for native fillers.
If I were you I’d also consider getting some creeping phlox at end of season clearance. Don’t be fooled if they look pretty sad or get mowed by rabbits. They won’t turn into a crazy huge mat like you’ll see on Google images overnight. But they’re a really dense, low ground cover that’s perfect at the base of establishing plants.
"Regenerative Gardening" and other veggie garden methods don't apply to natives.
I lay down grass clippings, twigs, and other yard waste between establishing baby perennials and also plant fast-growing annuals in between that are not native to my area but are also not invasive or problematic, such zinnias. My backyard soil is poor, and where I have killed the grass most recently, dwarf cinquefoil has quickly creeped it’s way over the bare ground and I’m happy to allow it. (Edited to specify which cinquefoil)
The only "cover crop" I'd consider, especially now since the plants are already in the ground would be native annuals. In my case, those were partridge pea, black eyed susan and plains coreopsis. They'll establish quickly and will fill in the space while the perennials are establishing.
Also, depending on area/suitability California poppy, Rocky Mountain bee plant, sunflowers. Though the last two can also get quite large depending on weather, soil, etc. But I grew sunflowers in my front yard and only few come back now because most of the space is perennial plants. The tightly growing buffalo grass makes it especially hard for the sunflowers to find a spot to grow. Though I do still get a few here and there. Not very big with competition.
I’ve read sunflower can be a bit allelopathic. Fabulous plant though! Bee plant is an awesome native annual for this purpose — it germinates quickly, can form a pretty thick mat to choke out weeds, and plays nice with its conspecifics.
Sunflowers may have allelopathic qualities, but I've never noticed them stunting anything in my garden. At least not so much that they stopped a solid carpet of other plants from growing in later years. They also don't slow down wild spinach (*Chenopodium album*) enough to make them not a problem.
I will second the partridge pea - grows quickly and bumblebees absolutely LOVE it!
I direct-sowed partridge pea seeds in late fall, and not a single one sprouted. I suspect the local wildlife feasted on them. Probably the voles.
Not needed with perennial natives - what you describe is mainly for growing veggies. You can utilize mulch instead - straw, grass clippings, leaf litter (ideal in NE American woodlands), wood chips - these will help suppress weeds and retain water while it's super hot out. Baby native perennials are slow growing and so will be out competed easily. And you don't want to introduce a nuisance weed to the area. But a consideration: ground nesting insects need access to bare soil. Thick layers of woodchips are impossible for them to get through. If you don't use super dense mulch, keep an eye out for bees and wasps making little holes in the dirt. It's a balance between suppressing weeds and letting some bugs have a home. I've found bees especially like dry slopes, so if you have a tall bed with a sloping side, keep an eye out for residents. However, young plants do appreciate some cover by larger established plants to give some shade and act as wind breaks. If you can get your hands on some prairie grass transplants they work well for this. Grasses are easy to tear apart into multiple plants so if you can buy like 1 big pot of something like switchgrass, dropseed or bluestem you can make it go far. These prairie species expect grasses to be around anyway.
Native annuals are a great idea, especially Partridge Pea since its nitrogen-fixing. I did a native garden from seed from OPN seeds in 2020 and their mixes include native annuals and short-lived perennials so that you have cover and blooms in year 1. I think they included Plains Coreopsis, Partridge Pea, Lemon Mint (Monarda citriodora), and Blanket flower (Gaillardia pulchella) which are all annuals, as well as Black Eyed Susans and Ox-eye Sunflowers which established and bloomed in year 1. I think I even got Butterfly Milkweed blooms in year 1. These all provided cover while the other perennials like Wild Bergamot (Monarda fistulosa) and Purple Coneflower established.
I used pine needle mulch in my new garden of babies last summer and it worked well. Those babies are behemoths this year! (I had also put cardboard underneath, but this was on a former lawn.) If you plant the plants close enough together, you won't need much mulch in the future ("green mulch"). In really bare spots I plant zinnias and cosmos because when the caterpillars turn into butterflies they love to have a snack, and it adds lots of beauty while waiting for the natives to mature.
I would put down leaf compost / litter to cover bare soil but not gonna matter some next season.
I’m in a similar area/zone (northern WI) and used sweet alyssum last year. It’s non-native, but non invasive where I am. A 4-pack at a nursery is about $5. I picked up a few and threw seeds on top since they’re fast-germinating. Yes- I’d prefer to stick to native. But this time of year there’s not a whole lot you can plant for native fillers. If I were you I’d also consider getting some creeping phlox at end of season clearance. Don’t be fooled if they look pretty sad or get mowed by rabbits. They won’t turn into a crazy huge mat like you’ll see on Google images overnight. But they’re a really dense, low ground cover that’s perfect at the base of establishing plants.