Leaving Some Weeds

A patch of "weeds" at the edge of my landscape. A lot of pellitory (Parietaria floridana) and some cudweed, etc.

Peppergrass - Lepidium virginicum

Cudweed - Pseudognapthalium obtusifolium

Weeds are always a bone of contention in a native plant landscape because we often differ as to what that means. Many of us are brought up to believe that a "weed" is undesirable or any plant growing in the "wrong" place. Botanically, those definitions tend to blur our discussion because weeds can be useful and they can grow in places we desire them to be. Weeds can be native or not. What makes a "weed" a weed is its growth habit. All of them share commonalities; most often the ability to quickly colonize open and disturbed places by producing huge amounts of seed. Weeds generally do not play well with others and given a bit of time and opportunity, they often overwhelm the more "behaved" species that we often typically wish to have in our landscape.
On social media and elsewhere, a common thread starts by someone asking what a plant is and then asking if it's native or not. Folks chime in and extol the virtues of the species in question. I often lose patience as I believe the first question after asking for an ID is what it will do in my landscape. Leaving a patch of "weeds" alone will most assuredly lead to the production of many more plants over time. I am not an anti-weedite, but I am fastidious about removing them from every part of my landscape that I have purposely planted with other things. As my wildflower area develops, I have been religious about removing the weeds - and I have been fairly successful. I continue to find a few, but the vast majority that emerged from the soil bank I disturbed by removing the turf grass have been eliminated. What I have mostly emerging now are seedlings from the wildflowers and native grasses that I planted there. My wildflower area is no longer arranged in tidy patches of various species, but is rapidly taking on its own design. This would not have happened if I had simply let nature take its course or if I had decided to let some of the weeds remain because they were native.
I do, however, have corners of my yard that are not planted that way and I have left some of them alone. They have value as larval host plants for various butterfly species that I would welcome to my landscape. The pellitory (Parietaria floridana) is a short-lived annual and spreads everywhere, but it is a host plant for the red admiral butterfly. The peppergrass (Lepidium virginicum) is also rather short-lived and serves as the host for the checkered and great southern whites. The cudweed (Pseudognapthalium obtusifolium), which pops up everwhere I don't weed it, is used by the American painted lady. In hopes of luring these butterflies to my yard, I can find a bit of space for them in the places at the edge of things. I've also left a bit of sida (Sida spp.) for the checkered skippers. A few weeds also serve well as nectar sources and I've left a bit of them as well - the matchweed (Phyla nodiflora) sometimes feeds white peacock caterpillars and Spanish needles (Bidens alba) is a host for several butterflies, especially the dainty sulfur. Leave no doubt, however, that these grow as weeds.
Many of the butterflies that use these weeds have other host plants that behave better and I tend to add these instead, but I have some room for the weeds outside my purposely planted areas. By allowing them space in my landscape however, I've also committed myself to a lifetime of serious weeding to keep them in their place.
I am a strong believer in purposeful planting. I believe we start with a plan and that we add those species that are best able to meet our objectives, but that said., there is always a bit of room for the weeds. Just realize that, if left to their own devices, they would take over the place...

Spanish needles (Bidens alba)

Matchweed (Phyla nodiflora)