March: when...then...

When pussy willows emerge all the way, that is a sign that maple syrup time is just about over for the year and that red-winged blackbirds have started to stake out their territories.
When maples flower and woodchucks dig up the hillsides, then ducks are scouting for nesting sites and onion sets can be tucked into the garden soil.
When coltsfoot buds in the hills of Pennsylvania and West Virginia, azaleas are past their prime in Georgia.
When you see aspens in bloom in the Rocky Mountains, watch out for grizzly bears emerging from hibernation.
When bleeding hearts are an inch tall, then look for purple cress blooming in the bottomlands.
When you see bumblebees and carpenter bees working in the flowers, then you know it’s time for termites to swarm.
Cabbage butterflies in your back yard announce that bass and sunfish are moving to spawn in shallow waters.
When you see golden forsythia flowering, then you know that middle spring has come to your township, and that the first major wave of wildflowers – the trilliums and bloodroots and Dutchman’s britches and more – will be in bloom throughout the woods.
When the rhubarb is up a few inches, then you know the daffodils are blooming and maples are coming in.
When raspberry and rose bushes are developing fresh leaves and wild onions are getting lanky, then bald eagle chicks are hatching and peregrine falcons lay their eggs.
When box elders bloom and pussy willow catkins get their pollen, watch out for the first mosquitoes to bite.
When magnolias are blooming in the Ohio valley, then Sandhill cranes are migrating in the Rocky Mountains.
When the mourning cloaks, the question marks, the tortoise shells and the cabbage butterflies come out, catfish are feeding and goldfinches are turning gold.
When you see the first monarch butterflies in your garden, and the iris start to bud, that’s the time to go out to the fields looking for armyworms, slugs, corn borers, flea beetles and leafhoppers.
When you hear the robin chorus an hour or so before dawn, then, when the sun comes out, look for green-bottle flies and garter snakes.

phenology from Poor Will's Almanack for 2011