As gardeners and farmers, we all know the feeling of watching our plants thrive during the warmer months and then facing the disappointment of seeing them wither away as winter approaches. But what if there was a way to continue growing and harvesting fresh produce even when the temperature drops and frost threatens? This is where low tunnels, a simple yet highly effective tool, come in handy to help you extend your growing season and enjoy year-round harvests. In this post, we will explore the ins and outs of low tunnels, including when and how to use them, the materials you'll need, and the benefits they offer for your garden. Plus, we'll highlight some ideal crops for low tunnel cultivation to get you started on your journey to year-round gardening success.

Low Tunnels: Your Season-Extending Allies

Low tunnels are temporary structures made of plastic sheeting draped over hoops designed to cover a single row of plants. These versatile structures provide a microclimate that protects your crops from the harsh elements, allowing you to grow plants well beyond their typical growing season. Low tunnels are especially valuable during the cooler months, both in early spring and late fall, when they can offset low temperatures and protect crops from excessive rain. Depending on your zone and other growing conditions, you may be able to extend your growing season by several weeks to months.

When and Why to Use Low Tunnels

Low tunnels are generally 2 to 3 feet tall and cover a single production row or raised bed. They are designed to provide protection from the rain, making them ideal for crops susceptible to mold and fungal diseases that thrive in moist conditions. Additionally, low tunnels create a warmer microclimate, promoting early flowering and fruit production in spring and extending harvest and growth periods in the fall.

Here are some scenarios where low tunnels are particularly useful:

• Early Spring Planting: By using low tunnels, you can get a head start on the growing season, planting cold-hardy crops well before the last frost date in your area.
• Fall Harvest Extension: Low tunnels allow you to continue harvesting well into late fall, ensuring a steady supply of fresh produce. Many cold-tolerant crops can also be sown in the fall season.
• Protection from Adverse Weather: They shield your crops from rain, frost, hail, and strong winds, reducing the risk of damage caused by these elements.
• Disease Prevention: Low tunnels minimize moisture on plant leaves and plastic mulch, reducing the spread of disease spores and promoting healthier plants.
• Increased Yield and Quality: The controlled environment within low tunnels can lead to higher yields and improved crop quality, resulting in more marketable produce.
• Ideal for High-Value Crops: Low tunnels are particularly cost-effective for growing high-value or heat-tolerant crops such as strawberries, peppers, eggplants, melons, herbs, certain cucumbers, and off-season greens.

Building Your Low Tunnel

Now that you understand the advantages of low tunnels, let's delve into how to build low-tunnels for your garden. Below, we'll outline the components you'll need and the step-by-step process:

Components of a Low Tunnel

• Hoops: Create sturdy hoops using galvanized electrical conduit, galvanized wire, or PVC. These hoops should arch 2-3 feet above the ground or soil level. Space 4-5 feet apart along the bed or row.
• End Anchors: Securely anchor the ends of the tunnel row or raised bed with metal pipes or poles, ensuring they are angled at less than 45 degrees and buried at least 2 feet deep.
• Plastic Cover: Choose a suitable plastic cover with a thickness ranging from 0.8 to 6 mil, depending on your specific needs and climate. Thicker plastics offer better durability, more UV protection, and longevity.
• Tunnel Support Cord: Use baling twine, rope, or bungee shock cord to tie down the plastic to each hoop, keeping it in place when raised for venting.
• Cord Hoop Support: Secure the plastic at the ends of each hoop using bent rebar, metal stakes, or metal eye hooks.

Building Steps

1. Install Hoops - Cut 10-foot-long galvanized electrical conduit (or other hoop materials) into 6-8 foot lengths and shape them into hoops. Insert the ends into the ground, spacing them 4-5 feet apart along the bed or row.

2. Set End Anchors - Place sturdy anchoring pipes or poles at both ends of the tunnel row, securing them at an angle of less than 45 degrees and burying them at least 2 feet deep.

3. Cover with Plastic - Drape the plastic cover over the hoops, ensuring it covers the entire width of the bed or row. Secure the ends of the plastic to the end anchors.

4. Secure with Tunnel Support Cord - Use twine, rope, or bungee cord to tie down the plastic at each hoop, making sure it is tight and secure.

5. Cord Hoop Support - Loop the cord or bungee cord through eye hooks or looped bolts at the ends of the hoops to further secure the plastic cover.

Management, Maintenance and Seasonal Care

Regularly check the tunnels to ensure they remain secure and to manage temperature and humidity for optimal plant growth.

Raise or lower the plastic cover based on temperature and ventilation needs. Use clips or clothespins to secure the plastic when venting. During the heat of the summer some crops may benefit from a shade cloth. This system can easily adapt to suport a shade cloth in place of the plastic covering once the weather warms up.

Remove any accumulated snow to prevent tunnel collapse and damage to crops.

Replace damaged plastic covers as needed to maintain effective protection.

Monitor and adjust watering and fertilization to accommodate the modified microclimate within the tunnel.

What Crops Grow Under A Low Tunnel?

Not all crops benefit equally from low tunnel cultivation. Here are some ideal candidates for your extended growing season:

Cold-Hardy Greens: Spinach, kale, chard, and lettuce thrive in low tunnels during cooler spring and fall months.

Root Vegetables: Carrots, beets, radishes, and turnips can be grown late into the fall

Herbs: Cilantro, parsley, and chives continue to produce well in low tunnels.

Brassicas: Broccoli, cabbage, and cauliflower can be harvested in early spring and late fall.

Strawberries: Low tunnels protect strawberries from winter frost, allowing for early spring harvests.

Solanaceae Family: Tomatoes, peppers, and eggplants are all heat-loving crops that can benefit from the increased warmth low tunnels provide during the early spring months.

Chelsea Hafer, True Leaf Market Writer

Chelsea is a passionate advocate for sustainable agriculture and loves getting her hands dirty and watching things grow! She graduated from Georgetown University in 2022 with a degree in Environmental Justice and now resides in Park City, Utah, where she works as a ski instructor. Her love for nature extends to gardening and hiking, and she has gained valuable insights from working on farms in Italy, Hawaii, and Mexico, learning various sustainable agriculture techniques like permaculture and Korean Natural Farming.