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A big pot can be a big problem for houseplants

"Fielding Questions" columnist Don Kinzler also answers questions about zone-hardy mum varieties and the varying prices of seed packs.

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A reader wonders if they used too large of a pot when they repotted this heirloom Christmas cactus.
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Q: I have a Christmas cactus that I got from my mother, and it’s about 70 years old! It has always looked good with big, thick branches. I repotted it a couple years ago, but it’s been going downhill ever since. I wonder if the pot is too deep. It’s 14 inches high and 16 inches across the top. The plant’s stems seem to be thin and big pieces fall off as though it’s rotting. I need help! — Bonnie.

A: I do think the size of the pot is too large. Christmas cactuses like to be "potbound" and can function better in a pot that's a little on the small side, versus being in a pot that's too large. Even with a very old Christmas cactus, the largest-diameter pot necessary is usually around 12 inches. It might be wise to repot into a smaller diameter pot.

Large pots tend to keep too much moisture around the roots, and the plant wallow in a soil volume that’s too great. Christmas cactuses, being succulents, like to dry out more between waterings than a large soil volume allows.

I always recommend starting new cuttings from an important heirloom plant. The cuttings are part of the original plant, so even if something happens to the original, the cutting still has all the makeup of the 70-year-old plant, except in a smaller form. Christmas cactus cuttings can be rooted in sand, perlite or vermiculite.

Q: I want to start some hardy perennial mum seeds that would be hardy in zone 3. Can you name some varieties and sources? — Michael D.

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A: Mums, short for chrysanthemums, are one of the most colorful fall-blooming perennials. They vary greatly in winter hardiness, so it’s important to choose cultivars that were developed for northern climates.

The University of Minnesota has been breeding mums since the 1920s, with an emphasis on cold hardiness. In the 1970s, the “Minn” series was developed in a range of colors with names like Minngopher, Minnyellow, Minnruby and Minnwhite. They grow in a neat mound shape to a height of 12 to 18 inches.

In the '90s, university breeders inspecting fields found seedlings of unprecedented size, and began marketing the “Mammoth” series, including Mammoth Lavender Daisy, Mammoth Red Daisy, Mammoth Yellow Quill and more. Growing larger than the Minn series, these mums can reach a height of 24 to 36 inches.

I’ve grown both of these mum series and they’re wonderful. Although these are the hardiest mums for Northern regions, they can still suffer freeze-out during cold, open winters. Allow the above-ground portions to remain over winter, and apply a protective mulch of leaves or straw in early November.

These hardy mum cultivars are propagated by cuttings, and so seed is not available. Check locally owned garden centers in the spring for starter plants. For best results, perennial mums should be planted in May so they have the entire growing season to grow and establish before facing winter. They will bloom beautifully the first autumn if planted in spring.

Q: Is there a difference in flower and vegetable seed packs that I see on the seed racks in stores this time of year? I notice some are much more expensive than others, and I’m wondering what the difference might be. — Bob L.

A: I’ve had reasonable success with both inexpensive and costly seed packs. There is a difference, though. The more expensive packets tend to be the newer varieties of flowers and vegetables, often with improved vigor, disease resistance, improved flavors, colors or other breeding characteristics. Less expensive packs tend to be the older varieties of flowers and vegetables.

Because our growing season is short and valuable, I prefer to spend a little more on quality seed for newer varieties with improved characteristics for most of what we plant in our flower beds and garden. I do however, still buy some older, heirloom types, too.

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If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at donald.kinzler@ndsu.edu. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.

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