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When to Plant Onions in Utah? - Wilson Garden

Understanding Utah's Climate and Soil Conditions

Utah Climate Zones

Onions thrive in cool temperatures. The planting window is between late March and early April. Gardeners in high altitude areas may need to wait after the frost. This potentially delayed planting until late April.

Ideal Soil Conditions for Onion

Onions prefer well-draining soil. Incorporating organic matter before planting. For example, compost or aged manure. This can improve fertility and drainage. Testing your soil pH level can also provide valuable insight. Onions prefer slightly acidic to neutral soil (pH 6-7). You can add lime to increase pH or sulfur to decrease it.

Soil Preparation

Consider incorporating a balance and slow-release fertilizer into the soil. Your onions will have the necessary nutrients throughout their growth cycle. Additionally, ensuring your garden has adequate sun exposure is vital. Onions require full sunlight to develop properly.

Types of Onions Suitable for Utah

Short-Day Onions need 10-12 hours of daylight. They are best suited for south Utah. While you can grow them in Utah, they might not achieve optimal bulb size. Because the state has longer daylight hours during the growing season.


Intermediate-Day Onions, needing 12-14 hours of daylight. They can perform well in most of Utah. For example, the areas with a balance between the northern and southern daylight hours.


Long-Day Onions require 14-16 hours of daylight. They are ideal for northern Utah. These varieties are perfectly adapted to the long summer days. This provides ample daylight for them to develop full, robust bulbs.


For gardeners in Utah, focusing on intermediate-day and long-day varieties yields the best results. Popular choices include Walla Walla, Yellow Sweet Spanish, and Copra. They are known for their adaptability and flavorful bulbs. These varieties can ensure a successful harvest.

Timing: When to Plant Onions in Utah

Northern Utah

In Northern Utah, including cities like Salt Lake City and Ogden, gardeners should aim to plant onions as early as March. This region experiences the last frost date around mid-May. So getting onions into the ground in March allows them to establish before the growing season.

Central Utah

For those in Central Utah, the window for planting onions moves slightly later. Areas such as Provo and Price can expect to plant onions from late March through early April. The slightly warmer climate compared to the north extends the planting season a bit. But early planting is still essential for a successful crop.

Southern Utah

Southern Utah, with its milder winters, allows for even more flexibility. Gardeners in St. George and Kanab can start planting onions as early as February. Due to the warmer temperatures and earlier end to frost threats, southern regions have an extended growing season. They are ideal for onion cultivation.

Factors to Consider

You must consider the regional climate and the current year's weather patterns. Soil temperature is a critical factor. Onions prefer cooler soil that has consistently reached at least 45°F. Additionally, understanding the local frost dates is vital to avoid planting too early or too late.

growing onions in utah

How to Grow Onions in Utah?

Preparation of Onion Sets or Seeds for Planting

You can plant onions from sets or seeds. In Utah, planting onion sets is generally more straightforward and yields quicker results. However, starting from seeds offers a wider variety of choices. It is more cost-effective.

Guidelines for Spacing and Depth

Proper spacing and depth are critical when growing onions in Utah. Plant onion sets or seeds about 1 inch deep into the soil. Space 4-6 inches between each plant. This gives the onions ample room to grow while ensuring they're not so spread out.

Watering and Mulching Newly Planted Onions

Water thoroughly to settle the soil around your plants. Applying organic mulch can retain soil moisture and regulate temperature. Onions have shallow roots. Ensure the soil remains consistently moist.

Caring for Onions Throughout the Season

Watering Frequency and Amount

Aim for about 1 inch of water per week when planting onions in Utah. You may need to water more frequently during dry periods. But be careful not to overwater. This can lead to bulb rot.

Fertilization Tips

You can add balanced fertilizer at planting. Then, apply every few weeks. For example, 10-10-10. You should avoid over-fertilizing. Too much nitrogen can promote excessive leaf growth and cause small bulbs.

Common Onion Diseases and Pests

Regularly check your onion crop. Pay attention to any pests and diseases. For example, downy mildew and onion thrips. Use appropriate fungicides or insecticides when necessary. Consider organic options to minimize chemical use in your garden.

Weed Control

Weeds compete with onions for nutrients and water. Mulching around your onion plants. This can help suppress weeds and retain soil moisture. Hand weeding or hoeing can be effective for weed control. But be cautious not to damage the onion bulbs.

Harvesting Onions in Utah

When to Harvest Onions in Utah?

Harvest when the tops of onions begin to fall over and turn yellow. This usually occurs in late summer. But the exact timing can vary depending on the weather conditions and the specific variety of onion.


Another sign to look for is the development of a papery outer skin. Once these signs are observed, wait for a dry period to begin the harvesting process. Because onions in wet conditions are more susceptible to rot.

Harvesting and Curing Onions

You can use a garden fork when harvesting onions. Gently lift them from the soil. Be careful not to damage the bulbs. Cuts and bruises can affect their storage life.


Curing involves drying the onions in a well-ventilated, covered area. This allows the outer layers to harden. The process will take two to three weeks. Place the onions in a single layer. Ensure enough space between them to promote airflow. Turning them occasionally will ensure even drying.

Storing Onions to Prolong Shelf Life

After the onions have been properly cured, trim off the roots. Cut back the dried tops to about an inch above the bulb. Store the cured onions in a cool, dry place with good air circulation. Mesh bags or netted sacks are ideal for storage. They allow air to circulate around the onions. Your onions can last for several months with proper store.

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