The crisp air of autumn often brings with it a twinge of sadness for gardeners, signaling the end of the abundant growing season. But what if the bounty didn't have to end? What if you could coax a few more weeks, or even months, of fresh, homegrown goodness from your garden, long after the first frost has arrived? This isn't a pipe dream; it's entirely achievable with the humble yet mighty cold frame and cloche. These simple, DIY structures are your secret weapons for extending the harvest, getting a jump start on spring, and even overwintering hardy plants. Join us as we explore how these ingenious tools can transform your gardening calendar, bringing you closer to year-round enjoyment of your own produce.
Understanding Season Extension Basics
At their heart, cold frames and cloches are miniature greenhouses designed to create a microclimate warmer than the ambient air. They achieve this primarily through two mechanisms: trapping solar heat and providing a physical barrier against cold winds, frost, and snow.
- Cold Frames: Think of a cold frame as a bottomless box with a transparent lid. Placed directly over a garden bed, it captures sunlight, warming the soil and air inside, much like a car parked in the sun on a cool day. The lid, typically angled, allows maximum light penetration and sheds water.
- Cloches: Cloches (from the French word for "bell") are individual plant covers. They offer localized protection, essentially creating a mini-dome of warmth and shelter for a single plant or a small cluster. They are particularly useful for protecting tender seedlings early in the season or extending the life of individual plants late into autumn.
The benefits of utilizing these simple structures are manifold:
- Earlier Starts: Get a head start on spring plantings by sowing seeds weeks before the last frost.
- Later Harvests: Extend your autumn harvest well into winter, enjoying fresh greens and root vegetables.
- Overwintering: Protect hardy plants, like certain herbs or perennial vegetables, through the harshest winter months.
- Hardening Off: Gradually acclimate indoor-grown seedlings to outdoor conditions before transplanting.
- Pest Protection: Offer a barrier against early-season pests and browsing animals.
- Cost Savings: Reduce your grocery bill by growing more of your own food for longer periods.
DIY Cold Frames: Your Mini-Greenhouse
Building a cold frame is a rewarding project that doesn't require advanced carpentry skills. The basic design involves a sturdy frame and a transparent lid.
Design Principles for Success
- Location: Choose a site that receives at least 6-8 hours of direct sunlight, ideally facing south, to maximize solar gain. Ensure it's level and well-drained.
- Dimensions: A common size is 3 feet by 6 feet, allowing easy access and fitting standard window sashes if you're repurposing. The back wall should be taller than the front wall (e.g., 18 inches at the back, 12 inches at the front) to create a gentle slope for the lid. This angle helps capture more sunlight in winter and sheds rain and snow effectively.
- Materials:
- Frame: Rot-resistant wood like cedar, redwood, or pressure-treated lumber (ensure it's rated for garden use and not treated with chemicals harmful to plants). Recycled bricks, concrete blocks, or even straw bales can also form the base.
- Lid: This is the crucial part for light transmission and heat retention. Old windows, polycarbonate sheets, or even heavy-duty clear plastic sheeting stretched over a frame work well.
Simple Cold Frame Construction Steps
- Site Preparation: Clear the area. You might want to dig down 6-12 inches and fill with a layer of gravel for improved drainage, then backfill with good quality topsoil and compost.
- Build the Frame: Cut your chosen lumber to size. For a 3x6 ft cold frame with a 6-inch slope:
- Two side pieces: 3 ft long, cut at an angle from 18 inches down to 12 inches.
- One back piece: 6 ft long, 18 inches tall.
- One front piece: 6 ft long, 12 inches tall.
- Assemble the box using screws or nails, ensuring it's square and sturdy.
- Attach the Lid: Create a simple frame for your lid from 1x2 or 2x2 lumber, matching the dimensions of your cold frame opening. Attach your chosen transparent material. Use sturdy hinges to attach the lid to the back of the cold frame. This allows you to open it for ventilation. Add a prop stick or an automatic vent opener to hold the lid open at various angles.
Table 1: Cold Frame Lid Materials Comparison
| Material | Pros | Cons | Cost | Durability |
|---|---|---|---|---|
| Old Window Sash | Excellent light transmission, often free/cheap | Fragile (glass), heavy, can be difficult to find specific sizes | Low to Medium | Moderate |
| Single-pane Glass | High light transmission, rigid, scratch-resistant | Very fragile, heavy, poor insulation value | Medium to High | Moderate |
| Polycarbonate Sheet | Lightweight, impact-resistant, good insulation (especially twin-wall), UV protected | Can scratch, opaque options reduce light, higher upfront cost | Medium to High | High |
| Plexiglass (Acrylic) | Lighter than glass, impact-resistant, clear | Scratches easily, can yellow over time, less insulating than polycarb | Medium to High | Moderate |
| Twin-wall Polycarbonate Film | Excellent insulation, lightweight, flexible, good light diffusion | Less rigid than sheets, requires framing, can tear | Medium | Moderate |
DIY Cloches: Individual Plant Protection
Cloches are the unsung heroes for targeted protection. They're perfect for shielding individual plants from sudden cold snaps, strong winds, or even curious animals.
Types of Cloches
- Bell Cloches: The traditional dome or bell shape, often made of glass or rigid plastic.
- Tunnel Cloches: A series of hoops covered with clear plastic or row cover, creating a mini-tunnel over a row of plants.
- Water Cloches: Specialty cloches (like 'Wall O' Water') that use water-filled tubes to absorb solar heat during the day and release it slowly overnight, offering significant frost protection.
- Homemade Cloches: Limited only by your imagination and available materials!
Quick Construction Ideas for Homemade Cloches
- Plastic Bottle Cloches: The simplest option. Take a clear 2-liter soda bottle or a milk jug, cut off the bottom, remove the cap for ventilation, and place it over a young plant. Anchor with soil or a stone if windy.
- Wire Hoop & Row Cover Tunnels: Bend heavy-gauge wire (like 9-gauge galvanized wire or rebar) into hoops spaced about 2-3 feet apart along a row. Drape clear plastic sheeting or horticultural fleece (row cover) over the hoops, burying the edges in soil or weighing them down with rocks. This creates a longer, continuous cloche.
- Old Container Cloches: Any clear plastic container (e.g., salad containers, deli containers) can be repurposed. Just ensure they are clean and have a way to vent.
Table 2: DIY Cloche Options Comparison
| Type | Pros | Cons | Best Use | Cost/Effort |
|---|---|---|---|---|
| Plastic Bottle/Milk Jug | Free, readily available, easy to make | Limited size, poor insulation, can overheat easily if not vented | Individual seedlings, quick frost protection | Very Low |
| Wire Hoop & Row Cover | Flexible length, good ventilation (row cover), lightweight | Less rigid, may require frequent adjustment, not fully waterproof (row cover) | Rows of greens, hardening off, insect barrier | Low to Medium |
| Water Cloche (e.g., Wall O' Water) | Excellent frost protection, good thermal mass, reusable | Bulky to store, can be tricky to fill and set up, higher initial cost | Protecting tender plants (tomatoes, peppers) from late frosts | Medium to High |
| Glass Bell Cloche (repurposed) | Aesthetically pleasing, good light, durable | Heavy, fragile, limited size, expensive if purchased new | Ornamental plants, small herbs, single delicate plants | Low (if free) to High |
What to Grow and When
The magic of cold frames and cloches lies in their ability to expand your growing repertoire and timeline.
Cold Frame Crops
Cold frames excel at growing and overwintering leafy greens, root vegetables, and hardy herbs.
- Leafy Greens: Spinach, lettuce (especially butterhead and romaine varieties), kale, arugula, mache, mustard greens, Swiss chard. These thrive in cooler temperatures and often become sweeter after a touch of frost.
- Root Vegetables: Carrots (small, quick-growing varieties like 'Paris Market'), radishes, and small beets can be planted for a late autumn or very early spring harvest.
- Herbs: Parsley, cilantro, and chives can be kept productive longer.
- Seedlings: Use your cold frame to harden off spring seedlings or start seeds for cold-hardy crops like broccoli, cabbage, and peas a few weeks early.
Cloche Crops
Cloches are ideal for individual plants that need a boost or protection.
- Early-Season Warm-Weather Plants: Give tomatoes, peppers, eggplants, squash, and melons a crucial head start by placing cloches over them after transplanting. This can buy you 2-4 weeks of growing time.
- Late-Season Tender Plants: Extend the harvest of bush beans, cucumbers, or even strawberries by protecting them from early frosts.
- Individual Herbs or Flowers: Protect a special herb or a tender annual from a surprise cold snap.
Table 3: Best Crops for Cold Frames & Cloches
| Crop | Cold Frame Suitability | Cloche Suitability | Timing | Notes |
|---|---|---|---|---|
| Spinach | High | Medium | Fall Planting, Overwintering, Early Spring | Very cold-hardy. Harvest outer leaves for continuous supply. |
| Lettuce | High | Medium | Fall Planting, Early Spring | 'Butterhead' and 'Romaine' types do well. Loose-leaf is easiest. |
| Kale | High | Low | Fall Planting, Overwintering | Becomes sweeter after frost. Can handle very low temperatures. |
| Mache (Corn Salad) | High | Medium | Fall Planting, Overwintering | Extremely cold-hardy, nutty flavor. |
| Arugula | High | Medium | Fall Planting, Early Spring | Quick growing, peppery flavor. Can bolt in heat. |
| Carrots | High | Low | Fall Planting, Early Spring | Small, quick-maturing varieties best. Mulch heavily for overwintering. |
| Radishes | High | Medium | Fall Planting, Early Spring | Very fast growing. Plant successionally. |
| Beets | High | Low | Fall Planting, Early Spring | Grow for roots and edible greens. |
| Swiss Chard | High | Low | Fall Planting, Early Spring | Very resilient, long harvest period. |
| Scallions | High | Low | Fall Planting, Overwintering | Can overwinter and provide early spring harvests. |
| Tomatoes (Seedlings) | Medium (for hardening off) | High | Early Spring (transplanting) | Protects from late frosts and gives a head start. Remove once stable. |
| Peppers (Seedlings) | Medium (for hardening off) | High | Early Spring (transplanting) | Similar to tomatoes, needs warmth for establishment. |
Seasonal Management and Care
The success of your cold frames and cloches hinges on attentive management, especially regarding temperature and moisture.
Ventilation is Key
This is arguably the most critical aspect of cold frame management. On sunny days, even if the ambient air is cold, temperatures inside a cold frame can quickly soar, "cooking" your plants.
- Daily Routine: On sunny days, open the lid of your cold frame a few inches (use a prop stick) when temperatures are above freezing (around 35-40°F or 2-4°C). Close it before sunset to trap residual heat for the night.
- Automatic Vent Openers: Consider investing in an automatic vent opener. These hydraulic devices open the lid as temperatures rise and close it as they fall, offering worry-free ventilation.
- Cloches: For plastic bottle cloches, simply remove the cap or lift them off entirely on warm days. Tunnel cloches with row cover offer natural ventilation, but plastic tunnels may need to be lifted or vented at the ends.
Watering Wisely
Plants in cold frames and under cloches generally require less frequent watering than those in open beds due to reduced evaporation.
- Check Soil Moisture: Always check the soil moisture with your finger before watering. It should feel slightly damp, not wet.
- Water Thoroughly: When you do water, do so thoroughly in the morning so plants have time to dry before nightfall. This helps prevent fungal diseases.
- Avoid Overhead Watering: Water at the base of the plants to keep foliage dry.
Pest and Disease Management
The enclosed environment can sometimes create conditions favorable for pests or diseases.
- Inspect Regularly: Check your plants frequently for signs of aphids, slugs, or powdery mildew.
- Good Air Circulation: Proper ventilation is your best defense against fungal diseases.
- Sanitation: Remove any dead or decaying plant material promptly.
Hardening Off
If you're using your cold frame to acclimate seedlings grown indoors, the process of hardening off is crucial.
- Gradual Exposure: Over 7-14 days, gradually increase the time seedlings spend in the cold frame, starting with a few hours on mild days and slowly extending it to overnight stays.
- Reduce Water: Slightly reduce watering during this period to toughen them up.
- Ventilation: Ensure good ventilation, exposing them to gentle breezes.
Winter Protection
For truly frigid nights or prolonged cold spells:
- Insulate the Frame: Pile straw bales, bags of leaves, or even thick blankets around the exterior of your cold frame to add an extra layer of insulation.
- Cover the Lid: On extremely cold nights, place a blanket, cardboard, or a piece of insulation board over the transparent lid for added protection. Remove it in the morning to let the sun in.
Practical Tips and Best Practices
- Site Selection: Always choose a spot with maximum winter sun exposure. A slight slope to the south is ideal for drainage and light.
- Soil Preparation: Fill your cold frame with a rich, well-draining soil mix that includes plenty of compost. Healthy soil means healthy plants.
- Temperature Monitoring: Keep a thermometer inside your cold frame. This helps you understand how quickly temperatures fluctuate and refine your ventilation schedule.
- Succession Planting: For continuous harvests, plant small batches of quick-growing crops like radishes or arugula every 1-2 weeks.
- Watering Frequency: In winter, plants may only need watering every 2-4 weeks, depending on the crop and how much sun they receive.
- Mulch: A layer of straw or chopped leaves around your plants inside the cold frame can help conserve soil moisture and provide additional insulation for roots.
- Labels: Don't forget to label your plantings! It's easy to forget what you've sown, especially with multiple successions.
Common Mistakes to Avoid
Even with simple structures like cold frames and cloches, a few common missteps can hinder your success.
- Lack of Ventilation: This is the most frequent culprit for plant failure. Overheating can kill plants faster than cold. Always remember to vent on sunny days.
- Overwatering: Excess moisture, especially in cool, enclosed conditions, invites fungal diseases and root rot. Err on the side of underwatering.
- Planting Too Early or Too Late: While season extension is the goal, pushing the limits too much can lead to disappointment. Research the cold hardiness of your chosen crops and respect local frost dates.
- Ignoring Pests and Diseases: The enclosed environment can be a haven for certain pests (like slugs or aphids) and diseases (like powdery mildew) if not monitored. Catching issues early is key.
- Not Hardening Off Properly: If you're moving seedlings from a warm indoor environment, a sudden transfer to a cold frame, let alone the open garden, can shock or kill them. Follow the gradual hardening-off process.
- Poor Drainage: Waterlogged soil is detrimental to most plants. Ensure your cold frame site and its internal soil allow for good drainage. If building directly on heavy clay, consider adding a gravel layer beneath your growing medium.
- Inadequate Sunlight: A cold frame or cloche won't work its magic without sufficient sunlight. Avoid shaded locations, especially in winter when the sun is lower in the sky.
Conclusion
The journey of extending your garden harvest into the colder months with DIY cold frames and cloches is a deeply satisfying one. It's about more than just fresh spinach in December; it's about reclaiming a sense of connection to your food, learning new skills, and defying the seasonal limitations often imposed on home gardeners. With a little creativity, some basic materials, and a commitment to daily observation, you can transform your garden into a year-round pantry. So, don't let the dropping temperatures dampen your gardening spirit. Embrace the challenge, build your own mini-greenhouses, and savor the unparalleled joy of harvesting fresh produce from your own backyard, even when frost glistens on the ground. Your garden, and your palate, will thank you for it!
