The experiment was carried out from April to September 2018 in Sujanagar village in Barlekha upazila of Moulvibazar district to observe the growth and biomass of the agar plants ranging from 1 to 15 years of age and soils characteristics of the plantation areas. Fifteen agar gardens were selected, and data were collected from 20 sample plants from each garden on growth, biomass, and soil nutrients. The plant height from bottom to top ranged from 1.11 m to 10.21 m, while it was 0.57 m to 4.80 m for the bottom to collar region height. The measured plant circumference ranges from 2.64 to 56.97 cm at the base (20 cm above ground level) and 1.59 to 32.27 cm at the collar region. The trend was similar for plant diameter, which ranges from 0.90 to 14.23 cm at the base and 0.53 to 9.14 cm at the collar region. The diameter at breast height ranges from 1.42 cm in to 12.32 cm in a 15 years old plants. From a 3 years old plants 3 years old plants to 15 years old plants, the estimated biomass ranges from 16 to 44 kg plant™. The plant height, branches, circumference, and biomass were found to increase in early-aged plants but became slow after eight (08) years. The pH of the soil was acidic (pH value ranging from 4.1 to 4.8), with organic matter ranging from 1.0 to 3.0% and N (%) from 0.09 to 0.15%. Available phosphorus and sulfur were found to be below the critical levels, with phosphorus ranging from 2.0 to 10.0 ppm and available sulfur ranging from 3.0 to 9.0 ppm. In the plantations, the exchangeable potassium ranged between 0.10 and 0.25 meqg/ 100g soil. The nutrient availability was found to be very low, which limits biomass production.