I was getting ready to order some of these, but then I read that they can be vigorous to the point of being invasive. What is your experience? If I go ahead and plant them, how deep and what is the best spacing?
Vigorous--Hopefully! Invasive---not here! Have been ordering those for a few years, along with several other specie Tulip's for fund raising purposes. All of the Tulip species are highly sought after here in my Zone, because they are perennial and none of the local outlets stock them.
Plant them 4-5" deep, 6" spacing. Makes a great Rockgarden plant!
Wouldn't worry about invasiveness and Enjoy!
For any Tulip to thrive and reproduce at all it must have a properly prepared bed, properly fed and watered and then properly cared for afterward. I am curious as to whether or not the plant you are describing is truly a Tulip at all? There are many common names for plants and plant types that describe a plant type that it is not. It would be possible I guess for a particular Tulip to become invasive given the right conditions, however highly unlikely. In doing a little research, I have found a few references of "little beauty tulips". Some of them were not Tulips at all, but were of different plant species altogether, but had a somewhat Tulip shape at some point during its blooming cycle. At least one of these references was for a species that we know here by the common name of "Star-of-Bethlehem". These are so invasive that I think it ought to be illegal to sell them.
This why it is important to use the botanical name for plants whenever possible. A place you might get more information on this is at the link below. They also have some pretty good information on spring-flowering bulbs in general and a pretty good newsletter.
Here is a link that might be useful: Gardening Resource
Little beauty is a 'botanical' tulip. Don't worry about it being invasive. How could you have 'too many'? If you don't like it or it doubles in numbers after a couple years... after it blooms just pull it out and 'voila'..gone. We have planted this little gem for years and have it throughout our garden.
A note: Little beauty is a common variety of botanical tulip. If you have a garden center or nursery nearby then this variety might be available without any special order. Even one of our box stores has it. Small botanical tulips are excellent for planting right over top or tucked into your mid to late season perennials. We tuck them down beside Sedum Autumn Joy, echinops, rudbeckia, echinachia and many other later plants. The little tulips are 'long gone' before they could interfere with the appearance of greenery or flowes of later bloomers.
I would never use the word invasive for a tulip. 'Little Beauty' is just that, a little beauty! I have them in my psuedo-rock garden and love them.