What cacti can grow without cold protection in USDA zone 6b in Pennsylvania?

Question

I'm in USDA hardiness zone 6b. I'm growing eastern prickly pears as outdoor perennials, and would like to grow some other cacti as well. From what I gather, cold hardiness has a lot to do with soil moisture levels, as cacti with a better water supply tend to get more cell wall ruptures, inducing rot and killing the plant.

In a cold, arid climate like North Dakota (zones 4-5), there is very little soil moisture going into the winter months, so there are several cacti that are native to the region.

I live in a far wetter climate, so conditions are harder here. But if I plant in a raised bed of mostly sand and organic matter, the drainage might be good enough for quite a few cactus species.

What cacti will grow well in this type of climate, with little or no care over the winter?

Answer 1

My neighbour grows opuntia species in USDA zone 4 (Canadian zone 5a) with lows to -40 deg C. The key seems to be good snow cover. This species has an extremely wide range from Texas to Alberta as seen in this link. If the winter weather brings unpredictable highs and lows and freezing rain then some die back is to be expected.

Opuntia fragilis alberta

Image courtesy of wikipedia

Answer 2

As was noted in the question, these cacti will not survive the winter with much moisture at all in the soil. They need water when growing, but over winter, they need dryness and light soil.

If I ever get this started, I'll probably put a hoop-house over the bed and cover it overwinter to prevent moisture from accumulating in the soil.

I did a little research, and here are the most interesting of the results I got, narrowed from a list about twice this long I have on notepad :):

• Escobaria vivipara, zone 7, Height: 6"

• Opuntia gilvescens 'Oklahoma Pancake' (Pancake Cactus), zone 6, Height: 15-40"

• Maihuenia poepiggii, zone 6, Height: 6-24"

• Escobaria missouriensis, zone 6, Height: 12"

• Echinocereus viridiflorus, zone 6, Height: 4-12"

• Sclerocactus spp., zone 6, Height: 6-10"

• Echinocereus reichenbachii, zone 6, Height: 6"

• Pediocactus simpsonii, zone 5, Height: to 10"

• Opuntia whipplei, zone 5, Height: 18"-2'

• Opuntia arenaria, zone 5, Height: 8-18", everblooming

• Hamatocactus bicolor, zone 5, Height: 6-12"

• Coryphantha vivipara, zone 5, Height: 6"

• Grusonia pulchella, zone 5, Height: 4-10"

• Opuntia polyacantha v. hystricina 'Bernalillo', zone 5, Height: 6-12"

• Opuntia davisii 'Copper King', zone 5, Height: 10-16"

• Opuntia phaeacantha x pinkavae 'Nambe Sunrise', zone 5, Height: 6-12"

• Opuntia rhodantha 'Chinle', zone 5, Height: 8-12"

• Opuntia imbricata v. arborescens 'Fred's Red', zone 5, Height:3-5'

• Opuntia imbricata v. arborescens 'Giant Form', zone 5, Height: 4-7'

• Opuntia imbricata v. arborescens 'White Tower' (White Flowered Tree Cholla), zone 5, Height: 3-5'

• Opuntia imbricata v. viridiflorus (Santa Fe Cholla), zone 5, Height: 2-3'

• Opuntia aurea 'Coombe's Winter Glow', zone 5, Height: 6-12"

• Opuntia clavata, zone 5, Height: 3-6"

• Opuntia leptocaulis, zone 5, Height: 1-5'

• Opuntia erinacea v. columbiana, zone 5, Height: 6-12"

• Pediocactus nigrispinus, zone 4, Height: 8"

• Opuntia humifusa, zone 4, Height: 4-8", water resistant

• Opuntia cymochila, zone 4, Height: to 14"

• Opuntia polyacantha v. polyacantha x fragilis 'Claude Arno', zone 3, Height: 4-8"

• Opuntia fragilis/humifusa 'East Meets West', zone 3, Height: 6-8", water resistant

• Opuntia cymochila x fragilis 'Smithwick', zone 3, Height: 4-6"

• Opuntia phaeacantha, zone 3, Height: 6-18"

• Opuntia debreczyi 'Apache', zone 3, Height: 4-12"

Answer 3

My potted Echinocereus reichenbachii has withstood multiple winters of zone 6 out in the open...rain, freezing rain, and snow.