Q: I have a sunny area with wet soil where I’d like to include some more native perennials. I have species for early and midsummer bloom but nothing yet for very late. Do you have a suggestion?

A: I think sneezeweed (Helenium) is underused and fits the bill nicely. Although its common name might make you think it’s a culprit of seasonal allergies, it is actually insect-pollinated. I’ve also heard it referred to as Helen’s flower, given the genus name, which probably gives it a more unbiased impression among people not familiar with it.

A denizen of wet meadows and sunny stream bank habitats, common sneezeweed (Helenium autumnal) blooms late, with a peak in flowering around September, though it may still have a little color as late as the end of October. The subspecies autumnal is found across Maryland, as is the fellow damp-adapted species Purple-headed Sneezeweed (Helenium flexuosum), though its peak bloom is around midsummer instead.

As an aside, our third and scarcer local species, Narrow-leaved Sneezeweed (Helenium amarum ssp. amarum), has a scattered distribution in Maryland’s coastal plain. Its native origin lies in the south-central U.S. As a summer annual, it has a comparatively long bloom season overall, which may provide a season extension into early autumn before a frost, but it prefers drier conditions and would not be a good direct substitute for H. autumnal or flexuosum.

There are multiple cultivars of common sneezeweed, and anecdotally, pollinators don’t seem to care about flower color changes in this case. Wild specimens tend to be completely yellow, but multiple cultivated forms include orange or orange-red in the petals or flower center. Mt. Cuba Center, a native plant public garden in the piedmont of Delaware, published trial results for Helenium a few years ago, which gardeners may find of interest regarding plant performance, cultivation tips, and popularity with pollinators. (mtcubacenter.org/trials/helenium/)

Q: I have a sapling shade tree in a pot that I’m taking care of until I figure out where to plant it. When should I bring it inside for the winter?

A: A cold-hardy tree, such as a volunteer native oak or redbud, should not go into the house. It’s too warm, too dry (humidity-wise), and the plant won’t get the seasonal cues it needs to develop normally and resume growth at the right time. Cold-hardy plants need to experience the chilling period of winter dormancy and changes in daylength (the influence of photoperiod I addressed last week) to stay in sync with the seasons, so they should be exposed to as much of a natural winter as possible.

One caveat for container-grown plants is that they are less tolerant of extreme cold or wild temperature swings than a plant in the ground. This is because the root ball for a potted plant is not well-insulated, and that degree of exposure will allow it to warm up or cool down much faster than anything in the garden, which may stress or even kill roots during freeze-thaw cycles. Coupled with the more rapid drying of potting mix in a container versus soil in the ground, this can result in branch dieback for shrubs and trees overwintering out of the ground. For broad-leaved evergreens like holly, it can also predispose them to more severe winterburn.

The motivation to protect a potted plant in the winter is helpful, but bringing it fully indoors is overcompensating and actually might be detrimental. Instead, you can reduce the risk of winter damage by heeling-in pots, which entails planting them in the ground with the pots still on so they are easy to pull back out again once temperatures moderate in spring. An above ground, dig-less version of heeling-in would be to use loose soil or wood chip mulch to build a mound around (and fill-in between the gaps of) a group of potted plants clustered together. Otherwise, buffer the roots from rapid chilling or premature warming by insulating them with a padding of unopened mulch or soil bags or with straw bales. If space is too limited for that, either tuck the pots against a sheltered wall of the house that will buffer them from the wind and rapid temperature changes, or try overwintering them inside an unheated garage.

Regardless of the plant’s location, don’t forget to check on it periodically for watering needs, as the potting mix should not be allowed to dry out thoroughly, especially before a freeze.

University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Extension” to send questions and photos.