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Hydroponic marigolds grow easily in most systems, from Kratky buckets to Dutch buckets and media beds, as long as they get full sun or strong grow lights. Marigolds ( Tagetes ) are fast annuals that germinate in about a week in warm conditions and bloom for months with deadheading. North Carolina State Extension lists African marigold ( Tagetes erecta ) as a full-sun annual, and UF/IFAS notes signet marigold seed germinates in about one week at 70–75°F. Compact French and signet marigolds are best for small indoor systems; tall African marigolds need deeper media and support.

Can vanilla hydroponics work? You can keep a vanilla orchid ( Vanilla planifolia ) alive and growing in a semi-hydroponic setup, such as clay pebbles (LECA) with a reservoir, much like other orchids. But growing vanilla for beans at home is a long project, hydroponic or not.

Hydroponic turnips are easy if you grow them for greens, and possible for roots with the right system. Turnips are a fast, cool-season crop: Texas A&M AgriLife lists turnips as a cool-season crop harvested about 40–60 days after planting, and notes temperatures above 75°F reduce yield and quality. Greens can be cut sooner. For greens, any lettuce-style system works, including raft, NFT, or Kratky. For roots, use a deep media bed or Dutch bucket filled with perlite, coco, or a perlite-vermiculite mix so the root has something to swell in and stays out of standing water.

Hydroponic tulips are grown by chilling bulbs, then setting them on trays or vases with their base just touching water or a dilute calcium nitrate solution until they root and bloom. It’s a real commercial method: Cornell University’s flower bulb program notes that about 30–35% of the Dutch cut tulip crop is forced hydroponically. The key is cold. Cornell describes giving dry bulbs about 75–80% of their cold requirement first, often 12–14 weeks depending on the cultivar, then rooting them in water at about 40°F for 2–4 weeks before moving them to warmth to flower, about three weeks later.

Hydroponic watermelon is possible in a greenhouse, high tunnel, or large indoor space if you grow compact personal-size varieties vertically on a trellis, support each fruit in a sling, and hand-pollinate. Use a large media-based system such as Dutch buckets with perlite or coco, rather than small channels, because vines grow big and roots need room. University of Missouri Extension gives 70–85°F as the optimal growing temperature for melons and watermelons and notes trellising allows higher plant populations in protected structures. Mini watermelons under about 6 pounds, such as seeded ‘Sweet Beauty’ or seedless minis, suit vertical growing best.