In central PA lawns we see the same handful over and over: dandelion, white clover, broadleaf and buckhorn plantain, creeping Charlie (ground ivy), wild violet, crabgrass, yellow nutsedge and spotted spurge. Most of them are a sign of thin turf, low mowing or compacted, wet soil as much as a weed problem.

Giant hogweed and wild parsnip have sap that causes severe burns and blisters when skin is exposed to sunlight. Poison ivy causes an itchy rash. Poison hemlock and jimsonweed are deadly if eaten. Each of those pages has a safety box. Never mow or string-trim giant hogweed or wild parsnip.

The PA Department of Agriculture keeps a Noxious Weed Control List. Plants on it, like multiflora rose, Japanese knotweed, tree-of-heaven and mile-a-minute, can't legally be sold, propagated or moved in Pennsylvania, and landowners may be required to control them. Use the PA noxious filter above to see them.

It depends on the life cycle. Crabgrass and other summer annuals are stopped with a pre-emergent in early spring, before soil hits about 55°F. Perennial broadleaf weeds like ground ivy and dandelion are easiest to knock out in early fall, when they move energy down into their roots. Winter annuals like henbit and chickweed are best handled in fall or very early spring.