I don't know if you want to have too much sand in your soil, though. I don't know how 'clayey' your soil is, as you put it. I'd probably be more apt to amend the soil so that it wasn't quite so clay-is and get it to the point where it was more free draining (which is probably what you want for the Lupines). I know that where I live our soil is more clay than anything else and that my hubby, who raises Plumeria, needs a quick draining soil as well (sounds like what the Lupines like, right?). He mixes his own soil mixture. Most people use a cactus mix because it is highly porous (has perlite and/or pumice). For our soil, if you want to break down the clay, you should add gypsum. That would probably be better than adding all the sand. Just a suggestion...

I wouldn't add sand either, ambbutterfly. I've added sand to heavy clay parts of my property when I wanted to plant something there, but it didn't change the soil, and plants didn't grow in it well. I think when you mix sand and clay (and bake it) you get bricks, don't you? :)
Gypsum would be good, like CalSherry said, also any type of organic matter. I've personally found that you can't change soil drainage that much anyway, except with raised beds. If you make raised beds with manures, compost, etc., and the soil in the bed is several inches higher than the surrounding soil, you'll get good drainage.
Sherry

I experimented some years ago with a course sand integrated in mixes in pots and had disastrous results. The sand compacted which didn't allow for good air flow and tended to hold water longer.

Incorporating gypsum is recommended by our state extension offices for clay soils. But like Sherry said using compost, barks, soil conditioners, and manures mixed into the soil will provide a much bettter growing media in your beds.

randy

I agree that organic matter is a better choice. But if you still want to add sand, make sure it is not fine play sand. You need use a rough builder sand.

Sand is useful for clay, but only when when you add so much sand so that the soil more sand than clay :P

I use a product called 'Dry Stall'...it's a volcanic rock similar to perlite but more like zeolite. Works awesome in my N Ca clay and the worms LOVE the stuff. Mulch with it and it cuts the weeds by tons, too...

Thanks for your comments everyone! After reading what you said, I'm not going to be buying any more bags of sand. I would like to get some gypsum but where do you find such a thing?