Q: The branches and berries in the photo are from one of three trees growing in a farm shelterbelt, where other trees died. These trees grew completely as volunteers, and are about 9 feet high and wide. Can you identify them, and are the berries edible? — Cindy K., Forman, N.D.

A: The shrubby trees are common buckthorn, whose botanical name is Rhamnus cathartica. Identifying features are the brown, pointed buds that have a uniquely distinct arrangement along the twigs, called "sub-opposite," meaning one bud is just slightly below the other, plus the white "lenticels" on the gray twigs.

Buckthorn berries are definitely not edible, and cause severe stomach upset if eaten. Birds, however, have different digestive systems, and nibble them readily. They often drop the seeds at a distance from the original source, which explains why buckthorn pops up in unexpected places.

Because they spread so profusely, buckthorn are considered an invasive species in many states. They can easily crowd out other vegetation, becoming thicketlike and growing to a large shrub or shrubby tree. They are also the alternate host of the disease oat crown rust, and buckthorn was more carefully rogued out when oats were grown widespread for feed and horse-drawn farm equipment was the norm. Without the attention to removal, buckthorn has become a problem in many areas.

Q: I have a few plants looking to upsize their living condition. Any advice on repotting a huge, 45-year-old Thanksgiving cactus without breaking it? The branches hang over the pot on all sides. — Nathan Larson, Fargo.

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A: Repotting large Thanksgiving and Christmas cactuses can be challenging. From the photo you sent me, the current pot looks about the right size, but if it's been in the same soil for years, fresh soil might be appreciated. Succulents don't like pots that are overly large.

If you're not going to save the current pot, it’s sometimes easier to break it with a hammer for easier removal, instead of trying to coax the trailing plant out of the container. Then remove a little of the old potting mix from the edges and bottom of the soil ball, slip the plant into a new pot and add a little fresh potting mix around the edges and a shallow amount on top.

Q: I’m moving and would like to take along some weeping willows that were only planted a few years ago. If I put them in 5-gallon buckets, how do I store them for the winter? Do they need sun? Can I leave them in the garage or bring them in the house? — Annette McIntyre, Moorhead.

A: As I write this, the ground isn’t frozen yet, so you'll want to dig them quickly.

The willows will survive better if kept dormant, so bringing them indoors probably isn’t the best approach. Warm temperatures would cause them to begin growing, and they would likely languish indoors from winter's low light and short days.

Keeping them cold and dormant will be best. Storing them in an unheated garage is a possibility, but garages can be problematic for storing plants because temperatures can fluctuate greatly as overhead doors are left open when warming cars in subzero weather.

The preferred option is to locate the potted trees outdoors next to the house foundation, but not on the south side, which can get too warm. Then, cover the bucket-type pots entirely with several feet of leaves, straw or shredded bark. The roots are more sensitive to cold than the top branches, so it's OK if the tops stick out of the mulch. You can either lay them down or leave them upright, as long as the root ball is well insulated.

When you move, take the frozen buckets along and winter them by the foundation at your new home. Then plant in spring.

If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at kinzlerd@casscountynd.gov or call 701-241-5707. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.