Gladstone Onion is a reliable, cold-hardy bulbing onion that thrives across a wide range of climates, from zone 3 through zone 10. This cultivar takes about 110 days from seed to harvest, making it a solid mid-season choice for gardeners who want substantial, well-developed bulbs. Growing it from seed indoors gives you the biggest harvests, with transplants moved outside well before your last frost date to maximize bulb size.
Full Sun
Moderate
3-10
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Gladstone performs across nearly the entire continental U.S., surviving harsh winters in the coldest zones while adapting equally well to warmer southern gardens. The 110-day maturity means you can time plantings to avoid peak summer heat in hot climates while still harvesting before frost in cold regions. Starting seeds indoors 10 to 12 weeks before your spring transplanting window gives you the edge on bigger bulbs, especially when soil temperatures hit that ideal 60 to 85 degree F range.
Gladstone onions are used fresh in the kitchen for cooking, raw slicing, and storage. Their moderate maturity span and cold tolerance make them equally useful for home gardeners in spring plantings and fall crops in warmer zones.
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Start seeds indoors 10 to 12 weeks before your average last frost date. Sow seeds 1/4 inch deep in seed-starting mix and maintain soil temperature around 60 to 85 degrees F for best germination. Transplant seedlings outdoors 4 to 6 weeks before your last frost date when they're established. The earlier you get plants in the ground, the larger your bulbs will be at harvest.
Transplant seedlings outdoors 4 to 6 weeks before your average last frost date, once soil can be worked. Space plants 12 inches apart in rows 12 inches apart. Soil temperature should be at least 45 degrees F, though 60 to 85 degrees F is ideal for strong growth.
You can direct sow seeds outside 4 to 6 weeks before your average last frost date, as soon as soil can be worked and reaches at least 45 degrees F, though indoor starting is recommended for larger bulbs.
Harvest Gladstone onions after 110 days when bulbs have reached mature size. Dig or gently pull bulbs from the soil and cure them in a warm, dry location with good air circulation for 2 to 3 weeks before storing.
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