Nasturtiums thrive in poor to average, slightly acidic, well-drained soil. If growing in full sun, consider using some rocks around the plants to prevent their roots from getting too hot. In partial shade, plants tend to have larger leaves and a more sprawling habit. Keep watered during dry weather, and do not fertilize. Continue reading below for more tips on how to grow nasturtiums from seed as companions for Brassicas, cucumbers, melons, radishes, and tomatoes.