Summer-blooming Dutch bulbs and perennials are not fussy about soil – provided it is not too heavy and sticky. If soil is heavy, loosen it with lots of humus, sand, gypsum, etc. If very light, add moisture holders – humus, peat mold, etc. If you have a soil with a high clay content, it can be improved by adding compost, peat moss or some other source of organic material. The organic material should be worked in the top twelve inches of soil (eighteen inches is even better).