You should have asparagus ferns cut back in late fall after they turn brown or in early spring before new spears pop up from the ground. The key is waiting until the ferns die back on their own first. Cutting green ferns too soon hurts your plants and reduces your next harvest.
I wait until my ferns turn golden brown and start falling over after a hard frost hits my garden each year in late autumn. This tells me the plant has pulled all the energy from those ferns back down into the roots for winter storage. The red berries on female plants should have dropped by this point in the season too.
The reason timing matters so much comes down to how asparagus stores food for next year in your garden bed. Those tall ferns work like solar panels all summer long for the plant below the soil. They turn sunlight into carbs that flow down into the roots for storage. Cutting asparagus foliage while still green stops this energy transfer too early and weakens your plants.
Think of early cutting the same way you would think of over-harvesting spears in spring from your bed. Both actions drain the crown's energy bank before it has a chance to fill up for winter. Your plants may survive the stress but they will give you fewer and thinner spears the next year.
For proper asparagus fern removal, cut all the dead stems down to ground level using sharp pruners or hedge shears. Pull all the cut debris out of the bed and throw it away or burn it if your area allows that. Old stems can harbor insect eggs and disease spores that will attack your new growth in spring.
If you miss the fall window you can still do cleanup in very early spring before things get going in your garden. Just make sure you get it done before the first spears start poking up from the soil. Working around new growth risks breaking those tender shoots before you get to eat them at your table.
Add a thick layer of mulch after you clear the old ferns away in regions with cold winters that last a long while. This extra cover helps keep soil temps stable through freeze and thaw cycles all winter long in your garden. Your crowns will stay safer under 4-6 inches (10-15 cm) of straw or shredded leaves until warm weather comes back in spring.
Read the full article: How to Grow Asparagus from Crowns Successfully
