A RARE TUBEROUS NASTURTIUM FROM THE ANDES

I’m sharing this curious vine which grows from a tuber with you all again as it continues to impress me, yet it remains rare in most collections. It’s a tuberous Tropaeolum, which isn’t botanically a nasturtiums but the genus for the common garden nasturtium is Tropaeolum. You may be able to identify some similar characteristics in the blossom – particularly the spur. Native to the Andes, the taxonomy of this particular species is as of yet, un clear – yet it looks very similar to one which was also grown at Kew Gardens identified as Tropaeolum x tenuirostre, but that is still under review by botanists. It may simply be a cross between two tuberous species, T. tricolor (tricolorum) and T. brachyceras.

These tuberous nasturtiums are getting more attention today by enthnobotanists and science as the interest in finding more sustainable food crops grows. One tropaeolum is already under consideration as a greater food source (Tropaeolum tuberous) which is commonly grown by native populations in the high Andes (Bolivia, Ecuador. Chile and Peru) along with the other Andean tubers which include Oca (Oxalis tuberosum), potatoes (Solanum tuberosum, S. juzepczukii), Papalisa or Ullucu (Ullucus tuberosus) and of course, the afore mentioned  Tropaeolum tuberosum,  which is often called Isaño or Mashwa.

If you remember, I grew both Oca (Oxalis tuberous) and Mashwa (Tropaeolum  tuberosum) last year, but the Oca found our growing season too short, and the tubers never matured, while the same could be said for the Tropaeolum tuberosum which never reached a mature size where it bloomed. I am holding out some slim hope that the tuber pulled itself deeper (as Dan Hinkley says it will survive if planted deeply) but with the wet and cold winter we have just experienced, I don’t expect it to return.

This tuberous tropaeolum is slightly different, as it is sometimes listed in literature as a food crop for high Andean tribes, it us usually only sourced as a low-resource food. One tuber per plant may be the limiter here, as one plant only produces a tuber the size of a golf ball.

 For the collector however, it delights – especially this rarer natural occurring cross or if it ends up being a distinct species, it always produces a spectacular floral show in late  winter and early spring, although it appears to be sterile – I cannot seem to produce seed.  It returns reliably in my cold greenhouse, whereas T. tricolor also returns, it rarely is vigorous (I have read that if planted in the ground, it will be more robust, so I may do that this summer while it is dormant). 

I repot the tuber ever two years, and this past year, I tried something different – which you can see in the middle image above – this year I double potted the pot, which may be unnecessary, but I wanted to experiment with the method, which is often used for alpine bulbs and plants – those which prefer either a fast draining soil, or one which needs to remain ever-so-slightly moist.

 I’ve read that these tuberous nasturtiums displace shifts in soil temperature, as such changes can trigger the plants to believe that the seasons have changed. With a double potting, maybe I will discover that the tuber will be more insulated (and delay and premature dormancy once our air temperatures rise in mid-spring).  The solid mixure that I used is 1 part sharp sand, one part Pro Mix and three parts large perlite, – it may help maintain the perfect moisture level while providing excellent drainage. My results so far are making me happy.