Last year I grew some Nassella tenuissima (syn. Stipa tenuissima) 'Angel Hair', from seed obtained from Thompson & Morgan (UK). Planted out last winter, in no time at all they were 90cm high and looking magnificent. However, once in flower the ground and any low growing perennials downwind of the Stipa were soon carpeted with seed awns to a depth of a centimetre or more. I collected and removed literally buckets full.
Although widely used in Northern European gardens, and frequently featured in show gardens and garden shows, Stipa tenuissima often carries a rather muted warning concerning its invasiveness. Nonetheless, there are masses of commentaries online which identify it as being a menace in some regions, whilst being well-behaved in others. Here, on the Costa Tropical (Granada) in Spain, it is clearly a vegetable vandal. I suspect the key might be that the climate on this short stretch of coast is not Mediterranean (Köppen type “Csa”) but is classified as “Hot semi-arid” (type "BSh"), which happens to be its native climate in Mexico! This Stipa, or should I say Nassella, feels perfectly at home here and it seems that I shall soon have a prairie.
Does anyone have experience of this and / or any advice? There are seven plants; should I remove and burn them or, as the damage is already done, should I leave them and see whether next year the problem is manageable by removing the seed heads as they appear? That is probably being over optimistic, as seed awns not only stick to any clothing but also to any leaves that blow across the seed carpet and then balls of seeds, the size of a grapefruit, roll around the rest of the garden! Mother Nature is certainly efficient.
I don’t anticipate any problems with Stipa gigantea, which I planted at the same time. However, I have sown and potted up both Stipa barbata and Stipa pennata ready for planting out this winter. In the circumstances, should either or both of those species be discarded?
