Gladiolus tristis has a lot of tiny corms around the mother corm so if you ever reuse the soil it is in you will have some of the babies in it and that is a source of new plants. If you remove it from the ground, you'll probably have some left. It is not invasive for me in my northern California garden in spite of its reputation. It doesn't even increase in great numbers like Freesia alba, Babiana hybrids, Moraea (Homeria hybrids), Geissorhiza inaequalis. I know it has that bad reputation, but I've grown some from seed and was given some and I've never had huge quantities in my garden. We saw it in the wild in large numbers in wet places so that may say something about it too. My soil dries out really quickly as it is sandstone mostly and the tree roots sap up the water. Perhaps that explains it. If you grow it you need to cut it and bring it inside to enjoy it's fragrance during the night as during the day it is not fragrant. I think it is important to be careful with plants that someone has labeled as weedy, but we all have different conditions so what is a problem one place may not be true elsewhere. I'm sure where it is colder than here Freesia alba would not survive and therefore would not be a problem. There are some things here we are very careful to dead head. Mary Sue