I agree with Neal. Planting in proximity of trees is great way for bulbs that require dryish summer conditions. A raised sand bed is another. However 'Purple Sensation' is very vigorous and I have the same experience regarding self seeding as Mika. Sometimes it does take an extra season to establish bulbs as they divide into small bulbs that need some time to attain a respectable size again. If you do think something is wrong, Terri, I'd dig a few of them after flowering(if they flower) and inspect the bulbs for anything suspicious - holes, discolorations and so on.
I read that
Allium schubertii doesn't produce any offsets and will die out after a few years, unless propagated from seed, but unsure if this is true or not as I also read the opposite
.
Allium karataviense is up for its third year here, but only a few of the bulbs have multiplied so far. They do get a little less sun than ideal, so could be that, but I suspect these were from seed so are genetically different in how freely they produce offsets.
The biggest allium casualty here was the drumstick allium. These are cheap and I bought a big bag of what I thought was a really easy species, but they only survived one year, so wasn't terribly rewarding here
Ambassador had a few bad bulbs when I replanted them last autumn, but the remaining are fine and of three original bulbs, there are five now. Mount Everest is another one in its second year and has multiplied from 5 to 15 bulbs in one year (not all of them flowering sized).
Globemaster usually produces two flowering sized bulbs from one every year. Occasionally there is a bulb that rots, but this is in the bed where I've lost almost all hyacinths as well, so suspect there is some pathogen present and I also water this area in summer so overall I think the result is very satisfactory as I still get more bulbs every year. So a long answer, but overall I think alliums can be wonderful returning bulbs and I have never lifted mine for summer, although that may not be a bad idea in some circumstances.
