Nasturtium and sweet alyssum seem to be more than warm season annuals. Like many other warm season annuals, they get established best if added to the garden just after winter, and then grow and bloom mostly during warm spring and summer weather. Then, if allowed to stay in the garden as cooler weather inhibits bloom somewhat , they survive through autumn and winter. By the time the original plants die out, new seedling emerge to replace them.
A potential ‘slight’ problem with allowing these annuals to naturalize (perpetuate naturally by sowing their own seed) is that fancier varieties eventually revert to a more genetically stable state. Sweet alyssum that can be various shades of pink or purple as well as white eventually blooms almost exclusively white after a few generations. Nasturtium that might start out with all sorts of shades of yellow, orange, red or brownish red eventually blooms with only basic bright yellow, bright orange and perhaps rarely, cherry red.
The reason that this is only a potential problem is that most of us are totally pleased with white sweet alyssum, and yellow and orange nasturtium! Another slightly more realistic potential problem with naturalization of sweet alyssum or nasturtium is that it leaves us no excuse to try different varieties. Anyone who doubts this should take a quick look through the online catalog of Renee’s Garden!
Nasturtium is easier to grow from seed than from small plants in cell pack, since small plants take time to recover from transplant. Besides only two or perhaps three of the multitude of varieties available as seed can be found in cell packs. Sweet alyssum can either be grown from cell pack or from seed, but like nasturtium, more varieties are available as seed. Although they grow throughout the year, both are still considered to be warm season annuals.
Busy Lizzy (impatiens), petunia, marigold, lobelia, cosmos and zinnia are some of the other popular warm season bedding annuals this time of year. Statice, cockscomb, verbena, moss rose and pincushion flower are also in season. Statice, tall varieties of cosmos and some varieties of zinnias make good cut flowers. Verbena, moss rose and pincushion flower are more often grown in mixed planting rather than as homogenous bedding. Although many more varieties are available as seed, cell packs of any of these warm season annuals provide more immediate results, especially this late in the season.