Nasturtiums bloom best in lean, poor-to-average, well-drained soil in full sun. Rich soil or heavy nitrogen feeding pushes the plant into lush leaf growth at the expense of flowers - the familiar 'all leaves, few blooms'. Go easy on feeding, and do not fertilise except on very poor ground.
Promising · suboptimal if ignored → advise
How it works
Rich soil and abundant nitrogen bias the plant toward vegetative leaf growth over flowering; lean, low-fertility soil shifts the same balance back toward bloom. It is the foliage-over-flower tradeoff that heavy feeding produces in many plants, here spending the plant on leaves instead of the flowers it was grown for.
What to do about it
Plant in average-to-poor, well-drained soil in full sun. Do not fertilise, and avoid nitrogen-rich feeding; reserve any feeding for genuinely poor ground. The engine does not invent fertiliser numbers.
How much it matters: No figure is stated or invented. The penalty is foliage instead of flowers on an otherwise healthy, vigorous plant, not plant failure. Because feeding is the gardener's own choice, the rule advises rather than warns.
The evidence
Evidence: confirmed against 2 sources in the research-based literature.
the 2 sources
Univ. of Wisconsin-Madison Extension (Wisconsin Horticulture), 'Nasturtium, Tropaeolum majus', hort.extension.wisc.edu/articles/nasturtium-tropaeolum-majus (read 2026-08-22): 'Do not fertilize, except on extremely poor soil, as high rates of fertilization promotes leaf growth and reduces flowering.'
NC State Extension Gardener Plant Toolbox, 'Tropaeolum majus', plants.ces.ncsu.edu/plants/tropaeolum-majus (read 2026-08-22): 'It grows best in poor to average, well-drained soil in full sun, but with some afternoon shade in hot summers'; 'Fertilizing will increase foliage, however, will also decrease flowering.'
Where this rule stops
A STANDING CULTURAL ADVISORY (trigger.kind always, gated to tropaeolum_majus by applies_to). It surfaces on the nasturtium species page and can be cited by the planting guides; it gates nothing and docks no score - the app cannot see how a bed was fed. It is the leaf-over-bloom parallel to the tomato feeding advisory, but for an ornamental/edible flower whose harvested output is the bloom itself.
Plants this fires on
Change history
Every change to this rule is one commit. This is what the project's version history records — the date and the reason — not a summary of it.
- nasturtium blooms on lean soil; rich soil gives leaves not flowers
Cite this page
Milpa Gardens. "Nasturtiums bloom best in lean, poor-to-average, well-drained soil in full sun. Rich soil or heavy nitrogen feeding pushes the plant into lush leaf growth at the expense of flowers - the familiar 'all leaves, few blooms'. Go easy on feeding, and do not fertilise except on very poor ground." Evidence grade: Promising. https://milpa.garden/rules/nasturtiums-bloom-best-lean-poor-average-well/
A garden-planning corpus: every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.