This study aims to establish whether lignin-treated soils could result in greater soil strength and stimulate seed germination and growth, which can be essential for slope bioengineering. Three different soil types with a range of plasticity were treated with lignin solutions of 1% and 3%. The changes in soil strength and seed growth were observed for 40 days to simulate the long-term field performance. Two methods to treat the soils were employed: Method 1 involved mixing lignin solutions with the whole soil sample, while Method 2 involved spraying the lignin solutions on the already-prepared soil sample. The results indicated that the lignin concentration and the soil treatment method could affect soil strength, whereas soils treated with 3% lignin solution using Method 1 consistently produced greater soil strength values. The lignin-treated soils were able to retain more moisture at the end of the experiment than the untreated soils. Both lignin-treated and untreated soils produced similar results on seed germination and growth, suggesting that lignin does not have a negative effect on slope bioengineering.