Why are weeds so successful?
Because the plants we call weeds are specialists in disturbed ground, and a garden is disturbed ground maintained deliberately — we create exactly the conditions they evolved for, then wonder why they arrive.
The traits that make a successful weed:
Enormous seed production. A single plant of many common weeds produces tens of thousands of seeds. One missed plant sets back years of work.
Long seed viability, with a persistent seed bank in the soil. Seeds of some species remain viable for decades, and every time you dig you bring a new cohort to the surface — which is the single strongest argument for no-dig methods and for mulching rather than cultivating.
Germination triggered by light and disturbance, so seeds wait, dormant, until conditions indicate open ground.
Rapid growth to flowering, completing a life cycle before slower plants establish.
Vegetative reproduction from fragments. Bindweed, ground elder and couch grass regenerate from small root or rhizome pieces, which is why rotavating a weed problem reliably multiplies it.
Deep or extensive root systems reaching water and nutrients that cultivated plants cannot.
No specialist requirements — they tolerate poor soil, compaction, drought and neglect.
Why they appear immediately on bare soil. Bare ground is an ecological vacancy, and the seed bank is already there. Nature does not leave soil bare, so anything you clear will be colonised by whatever germinates fastest.
What follows practically:
Cover the ground. Mulch, ground cover planting and dense planting deny light and space — far more effective than repeated clearing.
Never let them seed. Removing flowers before they set seed is worth more than perfect weeding later.
Disturb as little as possible, since digging is an invitation.
Remove perennial weeds completely, roots included, rather than chopping.
Hoe in dry weather while seedlings are tiny, which severs and desiccates them.
Reconsider the category. Many "weeds" are valuable for pollinators and some are edible — the definition is a plant growing where you did not want it, which is a statement about you rather than about the plant.