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barrowloads of thick white tubers out of the ground caused by alstroemeria
I do not understand your predicament. 
All the plants I've ever come across have roots, bulbs, or tubers of one sort or another below the ground 
From time to time some of them benefit from splitting or dividing and replanting to rejuvenate the clump. That's all 
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They can be vigorous - when I've grown them I tend to divide them every three years or so.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
You are quite right, Aym. I planted a handful of mixed alstroemeria, many years ago and they just went rampant. They grow through everything else and produce countless tubers. You can dig these up as often as you wish but you will never, never get rid of them. The only choices are learn to love them or move house....
Apparently you pull the flower stems like you would rhubarb which stimulates new flower growth and keeps your roots under control too
aym, if it's sterile it won't invade by seeding. You've found out for yourself that the roots are invasive.
In the sticks near Peterborough
A sterile plant is one that either doesn't produce seed at all or the seed isn't fertile, (won't germinate)
Invasive roots is another issue altogether.
Last edited: 13 November 2016 21:10:08
In the sticks near Peterborough
Mine produce lots of flowers and seeds, Aym, but I don't think the seeds germinate.They don't need to with all the tubers, I have clay soil which I have improved over many years so there is lighter topsoil but the blinking roots go way down through anything.
I bought a little selection years ago. They were all in the yellowy/orangey/pinkish range but only some rather darkish yellow/orange survived the first winter and they are the ones I still have . I do have some posher pink ones from Hayloft in a container this year, forget the name, but they will never be released into the garden!!
I'm surprised you have no flowers. Mine get full sun and the soil gets very dry but they love it. The bed they are in is about 12 ft long and 6ft wide and they have colonized the whole area despite my digging them out every year! I try to get groups of them rather than one solid mass and they are now at war with the agapanthus, fortunately another thug - I mean vigorous grower.
It sounds lovely. I have gaura and osteospermum but salvia really struggle and the slugs had the heleniums. All are over, now, anyway so I'm looking forward to next year.
Wow, they are magnificent. My old ones are Litgu Hybrids, just the orangey yellow one and my new one is Zoe. Zoe did really well for a first year, in a pot and still has flowers, but she has moved into the greenhouse for the winter, now. I shall have to divide and replant in spring but I'm still not sure about pitting her against my border plants!