Both cold frames and mini greenhouses are structures used by gardeners to help extend the growing season. They provide protection and warmth for plants, allowing gardeners to grow plants earlier in spring and later into fall. While they serve a similar purpose, there are some key differences between these two gardening tools.
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What is a Cold Frame?
A cold frame is an unheated outdoor structure consisting of a wooden or plastic frame with a transparent top. The transparent top, made of glass or plastic sheeting, allows sunlight to enter the structure and warm the soil and plants inside. Cold frames rely on solar energy to provide heat and protection.
Cold frames are often used to harden off seedlings that were started indoors. Hardening off is the process of gradually acclimating tender indoor seedlings to outdoor conditions before transplanting them into the garden. A cold frame provides a protected environment to help seedlings transition from the controlled indoor conditions to the variable outdoor climate.
In addition to hardening off seedlings, cold frames can also extend the growing season by providing extra warmth and protection for crops in early spring and late fall. Crops such as spinach, lettuce, kale and radishes can be grown longer into fall and winter in a cold frame. The frame helps retain heat and provides shelter from cold winds and frost.
Simple cold frames can be constructed from materials such as straw bales, bricks or cinderblocks for the sides, with an old window sash or plastic sheeting for the top. The goal is to create an enclosed space that traps solar radiation during the day and releases it slowly at night to keep plants warmer than outside air temperatures.
Key Features of Cold Frames:
- Unheated structures made of a frame with a transparent top.
- Rely on solar energy to provide heat and protection for plants.
- Often used for hardening off seedlings and extending the growing season.
- Made from simple, inexpensive materials like straw, bricks, plastic sheeting.
- Trap solar radiation during the day to keep plants warmer at night.
What is a Mini Greenhouse?
A mini greenhouse (also sometimes called a hobby greenhouse) is a small greenhouse structure used by home gardeners. Mini greenhouses are typically between 3-8 feet wide and 6-10 feet long, allowing them to fit well in small backyards.
While mini greenhouses are not large enough for major commercial crop production, they are excellent for starting seedlings, overwintering plants, and growing small crops. They provide more growing space than a cold frame and have a longer growing season since they retain more heat.
Mini greenhouses have transparent walls and roof panels, usually made of glass or polycarbonate plastic. The transparent panels allow sunlight in to provide heat and light for plant growth. Vents and doors provide ventilation to prevent overheating on sunny days. Heating and electricity can be added with a small portable heater or grow lights.
There are DIY options for building mini greenhouses from scratch using wooden or PVC frames. But most gardeners purchase prefabricated greenhouse kits that can be easily assembled. Kits allow you to choose features like the number of vents, benches, and accessories.
Key Features of Mini Greenhouses:
- Small greenhouse structures 3-8 ft wide x 6-10 ft long.
- Allow for seed starting, overwintering plants and growing small crops.
- Have transparent panels to let in sunlight and retain heat.
- Can add heating, ventilation, electricity as needed.
- Available as DIY build or prefabricated greenhouse kit.
Differences Between Cold Frames and Mini Greenhouses
While cold frames and mini greenhouses serve some similar functions, there are some notable differences between these two gardening tools:
| Feature | Cold Frame | Mini Greenhouse |
|---|---|---|
| Size | Typically 3-6 feet wide x 6-8 feet long. | Larger, around 3-8 feet wide x 6-10 feet long. |
| Construction | Made from simple materials like straw, plastic, old windows. DIY construction. | Prefabricated greenhouse kits, or DIY frames made from wood or PVC. |
| Walls | Typically 1-2 side walls. | Fully enclosed with transparent walls. |
| Temperature | Unheated, relies on solar radiation. Ambient air temperature. | Can add heating elements and better retain heat. Warmer than outside air. |
| Growing Season | Extends season moderately in spring and fall. | Provides significantly longer growing season from early spring to late fall. |
| Use | Hardening off seedlings, cool weather vegetable crops. | Seed starting, overwintering plants, more crop variety. |
| Cost | Inexpensive to construct from DIY materials. | Prefab kits range $100-$2000 depending on size and features. |
As you can see, while cold frames and mini greenhouses serve some of the same purposes, there are notable differences in terms of their size, construction, temperature control and growing capabilities.
Similarities Between Cold Frames and Mini Greenhouses:
- Provide protected growing area for plants.
- Allow for hardening off seedlings started indoors.
- Use solar radiation to provide heat and light for plants.
- Extend the growing season into colder months.
Key Differences Between Cold Frames and Mini Greenhouses:
- Cold frames are smaller and more basic constructions.
- Mini greenhouses allow for more growing space and crop variety.
- Mini greenhouses can add heating and electricity.
- Mini greenhouses have more temperature control and retain heat better.
- Mini greenhouses provide longer growing season from early spring to late fall.
Choosing Between a Cold Frame or Mini Greenhouse
When deciding between investing in a cold frame or mini greenhouse, consider these key factors:
Growing space needed
If you just need a little extra space for hardening off some seedlings and growing a few cold hardy crops like lettuce or spinach, a cold frame is likely sufficient. For starting lots of seedlings, overwintering larger pots of perennials, and expanding the variety of crops you can grow, a mini greenhouse will provide more growing capacity.
Length of growing season extension needed
Cold frames provide minimal growing season extension, just a few weeks on each end of the season. Mini greenhouses can greatly expand the shoulder season at both ends, allowing for up to 4-6 months extra on each end in some climates.
Level of temperature control desired
For basic protection from cool nights and winds, with temperatures fluctuating with ambient outdoor conditions, a cold frame fits the bill. If you want the ability to provide more consistent warmth for heat loving crops, the enclosed space and heating options of a mini greenhouse are beneficial.
Types of plants you want to grow
Cold hardy greens and root veggies that just need some extra frost protection can thrive in a cold frame. For starting tomatoes, peppers, cucumbers and other heat lovers earlier, or keeping tropical plants and citrus trees alive through winter, a mini greenhouse is a better choice.
Construction skills and budget
Handy gardeners on a tight budget can easily construct their own cold frame from scrap materials. Prefabricated mini greenhouses are more expensive, but require less DIY construction ability. Kits start around $100-$300 for small models, up to $2,000 or more for larger, deluxe options.
Considering these factors of growing space, length of growing season, temperature control, plant types, construction ability and budget will help you decide whether a cold frame or mini greenhouse better meets your gardening needs.
Conclusion
Cold frames and mini greenhouses both provide useful season extension and protection for plants in the garden. Cold frames are smaller structures that use solar energy to provide basic protection and minimal growing season extension. Mini greenhouses are more enclosed structures that offer expanded growing space, greater temperature control, and longer growing seasons from early spring to late fall.
Gardeners seeking minimal investment and simpler construction may opt for cold frames to harden off some seedlings and grow cool weather crops for a few extra weeks. Those willing to invest in a kit or DIY build and desiring greater growing capacity may prefer a mini greenhouse. Considering key factors like growing space, temperature control, budget and your specific planting needs will help determine which option best fits your gardening goals.