Planting outdoors - advice needed

I'm in Melbourne and want to plant some 'outdoor' cacti I've had in pots.  They're large enough that I don't want to lose them to Melbourne winter. What do you think?

Ferocactus Recurvus - 25cm wide incl spines
Echinocactus Grusonii
Ferocactus Histrix
Trich. Pasacana

The latter are all about 17cm tall.

My understanding is these are all hardy species.  Should I put them in the ground or wait till they're bigger?

HI Eck,

I've got a few large cacti planted out here in Melbourne inc Pachanoid, some trichs, oreo. celsianus, Cleistocactus strausii, some Feros but as I'm sure you are aware its location and drainage that are the issue. I've got several of the shorter ones planted out facing east in loam and with a little protection from the eves of the house. Provided you can ensure drainage I'd say you will be fine. I have a 45cm in diameter E Grunsonii in pot and its out in open exposed to weather all winter as well, only issue it had was when we had 15 min of golf ball sized hale a few years ago. That knocked the specimens out in the open around. All the ones you mentioned should be fine just don't plant them in heavy soil or the constant wet feet in winder could give you sleepless nights every time it rains. Where you thinking of putting them?

I'm pleased to hear you've had success with cleistocactus and oreocereus outdoors as I also have these species. I had always wondered because Collectors Corner labels say "covered outdoors".

I tend to go for columns and other large cacti as they're reasonably idiotproof (besides looking impressive). Until now I've kept them in pots under the roof eaves in winter and put them out in summer. But now they're getting large and I'm hoping to plant them. The soil here (if you can call it that) is basically hard clay and stones. Before planting anything the ground has to be broken up and mixed through with potting mix, composted grass clippings and such. Maybe it will be ok for large species cacti. I have Opuntia Ficus-indica in the ground but then nothing kills those!

That doesn't sound like the best soil type to work with. I'd go easy on the organics if you can as compost and grass clippings are high in nitrogen and also retain moisture and clay will already trap enough water and contain all the minerals they need. You need to work out how to keep the soil draining well in middle of winter when its been raining on and off for weeks. Also i've found just turning the soil and adding things like that doesn't help as it packs back down or rots over time but you can't turn it again once the plant is in place. Perhaps try building things up adding clay breaker and inorganic media which can improve drainage. Crushed scouria (spelling?) could be good here for example.

Head down to garden supplies and grab yourself a bunch of crushed granite (looks like grey dust) and a bunch of small scoria.. mix the two together and then work that into the planting site. . That will drastically reduce the water holding properties. Also build little mounds and plant the cacti in those that way most water will run off. .

Thanks for all the suggestions. It seems to me any hole I dig (to loosen up the ground for columns to get their roots in) is going to act like a water bucket due to the surrounding rocks/clay - at least until the clayish soil packs hard again.  I tried planting a lemon seedling in the stuff and it struggled all summer even with regular watering.  I put it back in a large pot and it's happy again.