Well, that's a loaded question for certain. But this is my (personal) experience, your mileage may vary, LOL
#1:
Xanthosoma saggitifolia is the only Xantho around here anyway that actually attains that tyoe of size. The way we get it to do it is lots of water and VERY HIGH HEAT

#2: ALocasias as a rule are not ALL large growing. There are some that will grow larger than others. The ones that get the biggest for me personally are the variegated albo-variegata, Portodora, and Sinuatis. Plumbea nigra can get very large, if it gets enough heat and a lot of water

#3:
colocasias, none of mine, even under optimal conditions, get over 3-4 feet tall, except Fontanessii, but they may get very large leaves. The ones thatgrow the largest get that way by having full sun and they grow IN WATER (as in, in a pond, sealed container of water, or natural bog)

Thanks,
I should have listed the ones I'm growing for size.
I have Alocasia odora, Alocasia marco, Alocasia calidora, (gonna order A.portidora), Colocasia 'Jacks Giant', Colocasia gigantea 'Thailand strain'.
I have a few others, but they are small and medium growers, and not really looking for any size out of them.
Thanks,
Kyle

All Alocasia, Colocasia and Xanthosoma require heat heat heat and more heat to grow big as the previous post states, the right light conditions (usually direct hot sun, but not with all Alocasia) lots of water during full growth and high nitrogen feed and MORE HEAT.

Ok thanks,
So what about about the pups/new shoots part of the question for encouraging most growth from main plant.

1. Divide pups as they come up, and give away.
2. Kill/squash pups as they come up through soil.
3. Bare root plant from time to time and remove runners/new shoots.

Option 3 i think.

OK, so the heat I can manage here in south Louisiana. It's been low to mid 80s for the past week. For the water, that'll come a little later in the summer (at least the natural stuff) and of course I've got a water hose to cover the dry spells.

But, specifically, are there any restrictions on what EEs should NOT be provided so much water? I think most of the colocasias (as Bihai said) would love to be submerged, but will be at least satisfied sitting in a tray to hold water. However, should the alocasias and xanthsomas sit in water also? Are there any that don't like having the wet feet?

Specifically, I've got A. calidora, plumbea and p nigra, macrorhizos, and X. violacea and 'Mickey Mouse'. Should any of these not get the water tray?

Thanks,
Dave

Hi Dave, I my experience Alocasia do not sitting in water, just moist soil when in full growth, Colocasia can be grown as marginal plants when in active vigorous growth but not Alocasia or Xanthosoma, just water these two as any other aroid, but dont stand them perminately in water because roots will rot.

Chris......over in the UK.

Thanks Chris -- exactly the info I was looking for.Dave

Dave, Of the Colocasia you are growing, do you grow Colocasia Gigantea 'giant Thailand strain' and Colocasia 'jacks giant'.

Sorry Chris, I'm not that fortunate (or experienced enough) to have obtained those types. Probably the best I can claim is that I have 'Nancy.'

They are just 2 excellent varieties available that you can get from 'Plant delights' and 'Brians Botanicals' that would probably do well for you in sunny Cal.
Both those nurseries are with you in the US and they do mailorder as well. Unfortunately i cannot get 'Colocasia Jacks Giant' here in the UK yet but hopefully one day.
Good luck with the gardening.
Chris.

Chris: how well do your Colocasias grow in your garden? I grow various Colocasia outdoors in my London garden (storing the tubers over winter and starting in the greenhouse in spring before planting out), but even in the decent summer we had 2 years ago they never attained any great size. Is it just not hot enough for them over here?

(I still love them for their beautiful foliage, even if they're not monsters.)

When I lived on the north California coast I had the same problem with lack of heat. Colocasia fontessia, and Alocasia calidora, and A. portidora seem to be an exception to this. Also heard that Alocasia wentii is a great cool climate grower.

Hello Ornata (London), My Colocasia dont get to the gigantic proportions that some people on this forum seem to achieve, (mainly in the US), Largest is probably Fontanesii and 'mammoth' that get about 4ft tall with 2ft leaves. I have ordered some potentially bigger varieties from Brians Botanicals via hiswebsite namely Colocasia 'Gigantea giant thailand strain', 'Jacks Giant' and A variety called Colocasia 'common form' which brian told me is anything but the coomon form because he reckons it grows to 10ft tall with 4ft leaves so abit of a misleading name on that one.
I am not expecting these 'giant' varieties to get to the same huge sizes as they manage in the US but 6ft with 3 ft would be nice.
Make sure you plant Colocasia in full hot sun with lots of high-nitrogen feed like Miracle-gro lawn feed for Maximum growth and if you have managed a 4/5ft plant with 2/3ft leaves in the garden in the UK you have done well.
Chris.