Will Zinnia or Marigold Plants Grow Faster Inside?

Starting Indoors

• Many gardeners start marigolds or zinnias indoors four to six weeks before the last frost. The seeds germinate in seven to 12 days when soil temperatures are around 70 degrees Fahrenheit. Plant the seeds 1/4 inch deep in light starting mix. Moisten them with water from a spray bottle and cover them with plastic wrap. Keep them in a warm place and moisten them regularly. Once they germinate, move them to a sunny window. Transplant them outdoors in late spring or early summer.

Benefits

• Starting annuals and marigolds indoors ensures that the plants will bloom from early summer through fall. Although seeds can be sown directly in the garden, their initial growth will be slower, and they won't bloom until several weeks later.

Growing Indoors

• Because zinnias and marigolds need full sun, growing them indoors for a prolonged period isn't recommended; they will not grow faster inside rather than out once they are established. The flowers' growth will slow, and the plants will become pale and spindly. For extended indoor growing, place the plants under fluorescent grow lights designed for plants. Grow lights are not aesthetically pleasing and most people store them in a basement or extra room, rather than in the main living areas. Grow lights are typically used to start plants or to provide supplemental light to plants overwintering indoors.

Recommendations

• Zinnias and marigolds need too much sunlight to make good houseplants. Start them indoors, but grow them outside for best growth and blooms. Plant them in full sun in fertile, well-drained soil, and water them as needed to keep the soil evenly moist. Fertilize zinnias and marigolds every three to four weeks with a water-soluble fertilizer. Discard them after the first heavy frost.