When to Transplant Broccoli Outside in Indiana

Transplanting Considerations

• Healthy broccoli transplants can withstand several frosts, but broccoli is not as hardy as other annual mustard family crops such as cabbage (Brassica oleracea var. capitata) and kale (Brassica oleracea var. acephala). As a rule, broccoli can be transplanted one to three weeks before your average last frost date of spring. You want your broccoli plants to be sturdy and well rooted when transplanting time comes, but you also need plants that are not pot bound or stunted from lack of nutrients in the potting soil. A good compromise age for broccoli transplants is about five weeks, so you should sow your seeds indoors about six to eight weeks before your last expected spring frost.

Growing Areas in Indiana

• The Purdue University Cooperative Extension Service divides Indiana into four large growing areas, known as areas A, B, C and D, with area A in the far south and area D in the far north. These growing areas are based on average last frost dates of spring, so they provide excellent guidance in regard to proper transplanting times across the state, especially for gardeners who do not have personal records for last frost dates in their area.

Transplanting Dates

• Gardeners in area A, which is a thin strip at the southern edge of Indiana similar to the region classified as U.S. Department of Agriculture plant hardiness zone 6b, should transplant broccoli from March 15 to April 15. In area B, which is another small section north of area A roughly equivalent to the region in USDA zone 6a, the recommended range is March 25 to April 20. In area C, which includes a large amount of the state's midsection, covering USDA zone 5b and part of USDA zone 5a, transplant from April 1 to May 1. In area D, which is a crescent-shaped section in the state's northeast corner that is mostly in USDA zone 5b, transplant from April 15 to June 1.

Choosing Within the Range

• Recommended transplanting periods tend to be quite long, ranging from about three to six weeks in Purdue extension's divisions. This is necessary to account for different microclimates and for variations in the weather from year to year. If your garden is in a low-lying area or is exposed to chilly winds, err on the side of late planting. Earlier planting is appropriate for hillside gardens, which are not as susceptible to frost, or for gardens with warmer microclimates created by windbreaks or southern exposure. Also, delay transplanting in years when early spring is cold, wet or excessively cloudy. All these conditions lead to cold soil, which causes slow growth after transplanting.