Jun 14, 2019

By Denise Seghesio Levine, UC Master Gardener of Napa County                                     


Reading about nasturtiums always confused me. Nasturtiums were described as easy to grow and “almost foolproof.” I tried starting them several times to no avail, and yet apparently everyone else knew the secret. This was borne out when my daughter-in-law planted several patches of nasturtium seeds in our garden and growing boxes and they grew. Seemingly easily.


Nasturtium (Tropaeolum minor) is an annual with peppery leaves and spicy flowers. You can find a variety of sizes ranging from tidy eight-inch mounding types to climbing or cascading varieties that can reach five feet in height. Unlike most lush summer plants that appreciate compost-rich soil with plenty of humus, nasturtiums will provide a much more luxurious show of colorful blossoms in sparse soil.  Fertile soil will give you lush green foliage, but you will miss the pops of color that make nasturtiums such a bright addition to the garden.


Nasturtiums are pretty, edible and protective, and they generously self-sow if they find their happy place. So it's worth the effort to get them going, and with Napa Valley weather just now finally warming, you still have plenty of time to get nasturtium seeds in the ground.


Plant nasturtium seeds one inch deep and about ten inches apart. You can plant in clusters of three and thin out all but the strongest seedling or take your chances and plant them singly where they will remain. Most of them will likely come up. Some gardeners like to soak nasturtium seeds before planting to speed germination. If you do, remember to soak them no longer than eight hours to avoid losing your seed to rot.


Nasturtiums like sandy, well-draining soil without too many nutrients, but they do like ample water. If you have planted them in beds, let them dry out a bit between each watering. Nasturtiums planted in pots seem to need watering more often than those planted in the ground and will appreciate a little dilute fish emulsion occasionally to replace the nutrients that frequent watering leeches out. Every site is different, so pay attention to how your plants are doing.  In my garden I have noticed that the plants that volunteer appear to be the most efficient water users.


Nasturtiums have rounded leaves with deep veins radiating from the center. They produce wide, deep-throated single or double flowers in oranges, yellows, creamy whites, maroons and reds. Nasturtiums are pollinator magnets and act as feeding stations for long-proboscis birds and insect nectar seekers. The leaves provide landing pads for a variety of other winged creatures.


Nasturtiums are butterfly host plants, attractive to many varieties as places to lay their eggs. Butterflies will lay their next brood's eggs often on the underside of nasturtium leaves, but sometimes on the top, hopefully hidden from predators. In about 14 days the larva will emerge, turning into caterpillars eating little holes in your garden's leaves.


One of my earliest memories of working at the Master Gardener Help Desk was taking a call from someone who had planted a butterfly garden but had no butterflies. A minute later she told me the other problem she had with her garden that year was an “infestation” of caterpillars, which she had finally eradicated. Unfortunately, those caterpillars would have been her butterflies.


Therein lies a very important lesson: Do not kill the caterpillars if you want butterflies.


But how can you tell which caterpillars are butterflies and which are just eating your cabbage and nasturtiums? The website Gardens With Wings (  has a tool to help identify the butterflies in your garden. Pick the main wing color of the butterfly flitting around your garden and click on the tab.  Up pop pictures of many butterflies. When you see your butterfly, you can see what its eggs look like and what the larva and eventually identifiable caterpillars will look like. It is a fun, useful tool that will help you learn to love caterpillars and to tend, nurture and support our fragile butterfly populations.


Nasturtiums can work in a variety of garden spots from partial shade to full sun. They also act as host plants for aphids, luring them away from your roses, kale and other brassica and cabbage crops. Most plants appreciate having nasturtiums around.


Nasturtiums do really well in our Mediterranean climate. Considered a summer annual, my volunteer nasturtiums were still blooming in December last year and were up and blooming again of their own volition by early May.  Now when people ask me if I grow nasturtiums, I tell them, “Sure, they are easy!”


Next workshop: “Succulents Celebration!” on Saturday, July 20, from 9:30 a.m. to 11:30 a.m., at the University of California Cooperative Extension, 1710 Soscol Avenue, Napa. Learn why succulents have become the trendiest members of the plant kingdom. For more details & online registration go to or call 707-253-4221.


The UC Master Gardeners are volunteers who provide UC research-based information on home gardening and answer your questions. To find out more about upcoming programs or to ask a garden question, visit the Master Gardener website ( or call (707) 253-4221 between 9 a.m. and noon on Mondays, Wednesdays or Fridays.