Abstract: In the horticulture, large amounts of growth substrate blocks are used for the growing of cuttings, and these blocks should preferably be surrounded by a paper like casing. For the very manufacturing of these block packaging the casing material should be of a reasonably strong and good quality, which, however, may cause problems later on, when the plant roots during their growth pack against the casing wall. With the invention there is used for the casing a dual fraction material comprising partly a long-time durable, open web and partly a reinforcing and more or less web filling or covering material of a type that is brought to disintegrate either in the manufacturing process or in a suitably rapid manner by the natural influences, in particular moisturing, to which the blocks are exposed when taken in use. Thereafter, the said web may hold the block together without preventing root penetration.