Ladbrooke’s handheld four-soil blocker with green comfort grip and the handheld four-soil blocker made for Johnny’s Selected Seeds receive high ratings by users. The Ladbrooke soil blocker is available on Amazon.com, as of 2015.
Soil blockers lightly compress potting soil to hold its shape, allowing gardeners to grow seedlings without pots. The seedlings are less prone to transplant shock because the roots are air pruned and do not get pot bound.
Commercial potting soil does not compress very well, so it is best to use a homemade mix. Johnny’s recommends 30 quarts of high-quality peat, 1/2 cup of lime, 20 quarts of coarse sand or perlite, 1 cup of blood meal, 1 cup of colloidal phosphate, 1 cup of greensand, 10 quarts of garden soil and 20 quarts of compost.