Turnips are a quick cool-season crop grown for their roots, their greens, or both. They handle light frost and are sown straight into the garden. The usual mistake is letting roots get too big: past about 3 inches across they turn strong-flavored, pithy and stringy.1, 2
The Florida Vegetable Gardening Guide gives January to April or September to October in North Florida, September to February in Central Florida and September to January in South Florida. Gardening Solutions gives August to February for North Florida, with the same central and southern windows. Sow directly; turnips do not transplant well. Broadcast in a wide row or sow single file. Gardening Solutions suggests 1/2-inch depth, seeds 2 to 3 inches apart in rows 18 inches apart, then thinning to 3 inches once seedlings are about 3 inches tall (eat the thinnings as microgreens). Seeds sprout in about five days. Plant closer if you only want greens.
Prefers rich, well-drained, deeply tilled soil. Turnips are fairly cold-hardy and tolerate frost and some freezing. Keep the bed weeded. 'Purple Top White Globe' is grown for both roots and tops; 'Shogoin' and 'Seven Top' are greens types that do not make large roots.
Greens can be picked through the season; just do not strip the plants. Roots mature in 40 to 60 days and are best pulled at 3 inches across or less. Smaller roots, around 2 inches, are milder.
The FAO manual names turnips among the larger bulb and root crops that are more likely grown in media beds, because NFT pipes and deep water rafts give them neither a good root environment nor enough support (p. 92). It also suggests growing root vegetables in wicking beds attached to media beds (p. 169). SRAC 454 does not mention turnips.
What this lesson doesn't cover yet
No UF/IFAS source fetched lists turnip pests or diseases; the section is empty.
No turnip-specific soil pH or fertilizer rate was found.
North Florida planting window conflicts: SP 103 says January to April or September to October; Gardening Solutions says August to February. Row spacing also differs (12 in vs 18 in).
Your county extension office and its Florida Master Gardeners can fill these in for your garden.