Is Heirloom good farm management software for the Southern Hemisphere?

Yes: your season runs on your calendar, not the northern one, so a July to June season plans as naturally as January to December. Heirloom is used by growers in 55+ countries.

At setup, or later in Settings > Season & climate, set Season starts in to the month your season begins, such as July for many farms in Australia, New Zealand, South Africa or Chile. A season is named after the year it starts in.

• Frost dates are suggested from your farm’s address: check them against your land and adjust.
• Climate-adjusted days to maturity follow your farm’s own climate, day length included, so your summers and winters shape the harvest dates.
• Plantings and sales channels that cross the new year, like a CSA running from November to March, work as they should.

See Set up your farm and Use climate-adjusted days to maturity in a planting.