Few annuals are easier to grow and have prettier flowers than nasturtiums (Tropaeolum majus). And yet I cannot get over excited about them. And although they are easy to grow, they are far less easy to grow well or make effective in the garden.
First, the positives. The seeds are large and easy to sow. You can start them in pots or sow the seeds direct where they are to grow. They are usually classed as hardy annuals but frost will kill the plants. Even so, the seeds, which are profusely produced, will overwinter and you will get lots of seedlings the year after you grow them. An early warm spell will make lots of the seeds germinate but a late spring frost will dissolve them. The plants thrive in sun and are usually recommended for dry, poor soils. Here they will grow and flower and are less likely to be leafy and vigorous than in rich soils. All parts of nasturtiums are edible and the leaves can be eaten as a spicy substitute for cress and the seeds can be pickled as a caper substitute. Perhaps the best way to eat the plants is the flowers which are also edible. Cress goes well with egg and the flowers stuffed with egg mayonnaise is an attractive and genuinely tasty combination. And if you are going to add flowers to your food at least nasturtiums look good and have a useful taste, unlike most edible flowers. *
Unfortunately, although easy to grow, there are problems. The mustard oils that give the plant its cress-like taste also attract the same pests as brassicas and cabbage white caterpillars will make a meal of the plants. And they are not the only pests that find the plants attractive. Blackfly are attracted to them and leaf miners like them too. It can be difficult to keep them looking in tip top condition.
Despite all this I grow one nasturtium every year. For 2015 I chose ‘Phoenix’. This is a Thompson & Morgan variety and obviously a descendant of the plants they sold a few years ago. I cannot remember the name of them then but they were sold as plants (this is strictly a tender perennial) with curiously fringed flowers. Despite the fact that they were supposed to be sterile these plants did set a few seeds and obviously T&M selected fertile plants from these so they could produce seeds. Unfortunately ‘Phoenix’ is not very stable and only about 25% of the plants I raised have been true to type, with indented leaves and frilly petals. The rest are ‘normal’ and, although not ugly, were not what was expected. In addition, although T&M state that the size is ‘Height: 30cm (12″). Spread: 35cm (14″)’ they are all far more than that. The largest have flung out stems 1m long and even the smallest plants, in the poorest soil, have shoots more than 60cm long. I used these to fill in gaps left because the poor weather left my amaranthus no bigger than when planted out and although they have filled in well they are too much leaf and not enough flower for my liking.
I like the flowers as much as the bees do but nasturtiums are just too thuggish for me to love them, even if, as has happened this year, most insects have left mine alone.
* make sure you shake out any insects such as pollen beetles before you eat the flowers.