Nasturtiums bloom best in poor soil. Photo: store.underwoodgardens.com
Question: I bought nasturtiums for my two flower boxes. For three weeks, the boxes have been filled with very large leaves, but only one flower per box. I added compost and flower fertilizer, but it doesn’t seem to help. What should I do?
Answer: The nasturtium (Tropaeolum majus), unlike almost any other annual flower, simply doesn’t like rich soils. A soil too rich in minerals, especially nitrogen, the first number of the three that we see on ferilizer labels, tends to produce an abundance of beautiful and very lush leaves, but very few flowers. Other factors to consider would be too little light (it prefers full sun) and overly sparse watering, but usually the combination of beautiful leaves and few to no blooms flowers simply means the plant is being overfed.
So, for this year, simply stop fertilizing. The concentration of minerals will eventually decrease and more abundant flowering should begin. As for next year, sow or transplant your nasturtiums into ordinary container soil mix, without adding compost or fertilizer, and you should see the plants in full bloom right from the beginning of the season.