Figure 8 shows an area of nettle plants - Edexcel - GCSE Biology - Question 5 - 2019 - Paper 1

Grass does not grow among nettles primarily due to competition for resources. Nettle plants have a robust growth pattern and can overshadow smaller plants like grass, restricting their access to sunlight. Additionally, nettles may produce allelopathic chemicals in the soil that inhibit the growth of nearby plants, including grass. Finally, the dense foliage of nettles can also create an environment that is less favorable for grass growth, as it competes more effectively for nutrients and space.