I've been trying to grow trailing nasturtiums in hanging baskets inside my greenhouse, and they started off great, sprouting fast and looking healthy. However, they've stopped growing at about 6 inches tall and aren't blooming at all. Normally, these nasturtiums can grow up to 6 feet when planted outside here in the Pacific Northwest. My greenhouse stays around 70 to 75 degrees all day and night, and I have full-spectrum grow lights about 2 feet above them that run for half the day. I've been using Miracle Grow moisture-control potting soil but haven't added any fertilizer since I heard nasturtiums don't respond well to it. They have plenty of space in the baskets, but I'm wondering if they just need more natural sunlight to thrive like they do when planted outside.
4 Answers
Make sure you actually have trailing nasturtiums! Some varieties, like the Indian Princess, are bush types and won’t trail like you expect. I made that mistake once myself and it was a disappointment!
The hanging baskets might not be giving them enough room to grow since nasturtiums have extensive root systems and prefer to sprawl in soil. They usually thrive much better when planted directly in the ground where they can spread out.
Be careful with the Miracle Grow moisture-control soil since it already has fertilizer in it! It’s probably best not to add more. Your seedlings might just be focusing on developing their roots before growing the leaves. Regarding your grow lights, those could be closer—around 4-6 feet from the plants could encourage better growth if they’re strong enough, around 4,000 to 6,000 lumens should do it. I love growing trailing nasturtiums as ground cover; they can be really beautiful!
It sounds like your nasturtiums are just pausing for the right conditions to grow. They tend to have a sense of timing, and they may be waiting for warmer temperatures to encourage further development and blooming. You mentioned they do great in May outside, so it could be similar in the greenhouse too!
Exactly! I often get volunteer nasturtiums from my compost, and they sprout early but wait until it warms up before taking off.