Winter is coming, but there will be days when our warm Colorado sun allows us to spend time in the garden.
Once a hard frost sets in, herbaceous plants may blacken and shrivel, and you may wonder how much of this you should clean up. Like most questions, the answer is it depends on what you are growing and what you want to achieve. Plants don’t need the cleanup; we clean them up to get the outcomes we want, more flowers or fruits, and better aesthetics.
If you are vegetable gardener, cleanliness is next to disease-free crops. Vegetables are susceptible to many viral, bacterial and fungal diseases. Debris left in place in the garden gives these microorganisms a place to shelter and survive winter. Cleanup minimizes the probability of these organisms damaging your plants again next spring. Remove all plant debris once it is no longer producing. Cultivating and amending the vegetable bed now is a good idea. You will be ready to plant cool season vegetables, like lettuce and spinach, as soon as the soil warms up in spring.
Ornamental grasses can be cut back in either early or late winter. Unpruned, they provide winter interest with seed heads peeking up over the snow. Grasses can provide some seeds for birds. However, large grasses can also provide shelter for small rodents like mice or voles. If these are a problem in the garden, cutting back in late fall may be a better option. If you do not prune ornamental grasses back at all, they will revert to their natural growth habit of a dead center, surrounded by new growth in an outer ring —not an attractive look.
Perennial flower gardens offer choices. You can clean up in autumn and have less work to do in spring. If cutting back and cleaning up in fall, make sure you leave green foliage in place. Just remove brown stems and spent flowers. Leaving the foliage will provide some insulation and minimize moisture loss to the roots. If your garden includes plants that are marginally hardy, they will be hardier if they are not cut back. Mulching perennials with shredded leaves or grass clippings can be helpful by moderating the big temperature swings our climate is infamous for, especially for marginally hardy plants. Mulch also helps with moisture retention.
If you choose not to do a fall cleanup, the advantages are benefiting wildlife with seed heads, encouraging reseeding for next year and more winter interest. If you have plants that have been plagued with pests such as aphids, or fungus, cleaning up before winter can deprive these pests of overwinter shelter. You can selectively clean up the effected plants.