Hey, Toronto gardener here, aiming for an easy perennial garden that comes back year after year. Gladiolus is a prime choice for me (low maintenance and beautiful, and I’m in a zone 5-6 area (Scarborough).
As I am frequently out of country (and own several rentals), I was wondering – how dangerous is it to leave the bulbs in the ground?
I’ve heard mixed things. Is there a cultivar that I can safely leave in the earth year after year?
If not, any suggestions on alternatives?
I’m not sure what you mean by “dangerous” – i.e., dangerous to squirrels and other animals, or to small children who are naturally curious and put everything in their mouths?
Of note, gladiolus bulbs (called corms) can cause symptoms that include nausea, vomiting and skin irritation, according to the University of Wisconsin Health Wisconsin Poison Center “Common plants – what’s poisonous and what’s not?”. This publication also includes lots of non-toxic plants.
Penn State Extension “Spring plants that are poisonous to horses, dogs and barn cats” states that gladiolus corms can cause salivation, vomiting, drooling, lethargy and diarrhea in cats and dogs, if ingested.
If by “dangerous” you mean”, risks the winter killing the plant”, gladiolus corms should not be left in the ground year-round, as most varieties are hardy in zones 8a-11. They are usually planted in mid-May through mid-June, so that flowers will bloom through July & August. Once the foliage has been killed off by frost, the corms should be dug up and stored.
If you wish, leave a few corms in the ground over winter as an experiment, chances are they will rot in the cold soil, but some growers indicate that gladiolus can over-winter in the ground, even to zone 5. However, this would not be predictable, so you could be gambling each year that the corms would survive the winter. That being said, mulching the gladiolus could protect them from the winter weather, and if your properties are blanketed with a good (insulating) snow cover, the corms would have a better chance of surviving. The Gladiolus nanus ‘Atom’ is hardy in zones 6-10 (needs thick mulch covering where winters are extreme). It grows to around half the height of the gladiolus most of us are used to.
If you decide against gladiolus, see “Long blooming perennials: a Toronto master gardeners guide “. I have found Geranium ‘Rozanne’ to be super-easy to maintain, while blooming over several months.
See also the Missouri Botanical Garden’s “Perennials for season-long bloom“, which may give you some ideas.