Species of Gelidium are important sources of agar. Mass cultivation of Gelidium spp. has been elusive. Development of techniques to seed thalli in the natural environment could be used to increase in stocks and landings. Gelidium lingulatum is an important seaweed resource in central Chile, growing on the lower levels of exposed rocky intertidal shores. Experiments were done to evaluate fragmentation of the thalli and the effect of some factors on the production of secondary attachment structures (SAS). When experimentally exposed to high water flow, thalli became frequently fragmented, mainly at the level of the creeping axes. Comparisons among parts of the thallus indicated that creeping axes produced more SAS than blades and reproductive branchlets. Similar results were obtained on the three types of substrata tested (rock, barnacle shells, and mussel shells). After 7 days of incubation, more SAS were produced under low than high irradiance (8 and 80 μmol photons m−2 s−1, respectively). Also, a small increase in dissolved calcium (0.5 mM) in the medium enhanced SAS production, but higher levels (2.0 mM) had an inhibitory effect. Higher temperature (15 °C) tended to favor SAS formation when compared to lower temperature (9 °C). For these three factors, differences in the density of SAS were reduced or disappeared after 14 days of incubation. Different seasonal series of each experiment had consistent results. Recommendations are made for the application of these results to seeding of thalli of G. lingulatum on the rocky shore.