Step 5 - Greenhouses
Greenhouse vs Cold Frame
For the jobs a first greenhouse usually does, a cold frame is a tenth of the price. The difference is standing room and scale.
Janet H. - the hands-on owner behind Janet Media Group.
Published - last updated
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Buy a cold frame if you want to harden off seedlings, start spring sowings early and carry hardy greens through winter. Buy a greenhouse if you want to stand up in it, work in it in bad weather, and grow crops to maturity under cover.
| Cold frame | Greenhouse | |
|---|---|---|
| Cost | Low | Several times higher, plus the base |
| Standing room | None -- worked from above, kneeling | Yes |
| Hardening off | Ideal | Works, but oversized for the job |
| Early spring sowing | Yes | Yes, and more of it |
| Overwintering hardy greens | Yes | Yes, more comfortably |
| Growing to maturity under cover | No | Yes -- the main reason to have one |
| Working in bad weather | No | Yes |
| Site prep | None -- it sits on a bed | Level base, anchoring, sometimes a permit |
| Venting | Manual, or a small auto opener | Roof vents, ideally automatic |
Quick picks
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 |  Top pickVIVOSUN Cold Frame Mini GreenhouseLow-profile frame with hinged clear lid | Extending the season over a bed | 8.0 | Check price on Amazon |
| 2 |  Palram Canopia Mythos GreenhouseAluminum frame, 4 mm twin-wall polycarbonate | A first real greenhouse | 9.0 | Check price on Amazon |
| 3 |  Min/Max Greenhouse ThermometerRecords the high and low since last reset | Knowing what actually happened overnight | 8.6 | Check price on Amazon |
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Scores are our own editorial judgment, formed from published specifications and independent sources. They are not aggregated customer ratings, and they are not the result of hands-on testing, which we do not currently do. See how we choose.
What only a greenhouse does
Height and volume. A greenhouse lets you grow tomatoes, cucumbers and peppers to maturity under cover, which is the thing a frame fundamentally cannot do. It also gives you somewhere to work in the rain, which matters more in practice than it sounds in a list.
It holds temperature better, too, because of the larger air volume -- though neither structure is heated, and both live within a few degrees of outside overnight.
What a cold frame does better
- Cost per job done. For hardening off specifically, nothing else comes close.
- No site preparation. It sits on an existing bed. No base, no anchoring, no permit conversation.
- Storage. It folds or lifts away out of season, which a greenhouse cannot.
- Proximity to the crop. A frame sits directly over the bed the plants are already growing in.
Both, actually
The common end state is a greenhouse plus one or two cold frames. The greenhouse raises seedlings and grows tall crops; the frames sit on the beds and handle hardening off and winter greens where the plants already are.
If budget is the constraint, buy the frame first. It is the cheaper experiment, and it tells you whether you will use protected growing at all before you commit to a structure.
For frames, see cold frames. For kits, the best greenhouse kits.
The picks in full
Top pick
VIVOSUN Cold Frame Mini Greenhouse
VIVOSUN
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A lid for a corner of a raised bed: no assembly worth the name, and the cheapest few weeks of extra season you can buy.
A cold frame is the least glamorous and most cost-effective piece of season-extending equipment in the garden. It is a box with a transparent lid: sunlight in, wind off, a few degrees of overnight protection.
Used over the corner of a raised bed it will carry spinach, mache, and hardy lettuces through a cold spell, harden off seedlings before they go out, and start spring sowings a couple of weeks early.
The one discipline it demands is venting. A closed frame on a sunny March day can cook its contents by lunchtime. Prop the lid in the morning, close it in the late afternoon.
What works
- Cheapest real season extension there is
- Works over an existing raised bed with no site prep
- Good for hardening off and for overwintering hardy greens
- Stores flat out of season
What does not
- Overheats fast on a sunny day if you forget to vent it
- Small growing area
- No standing room at all
Skip it if: you need headroom. A cold frame is worked from above, kneeling, with the lid propped open.
| Type | Low cold frame with hinged lid |
|---|---|
| Glazing | Clear panel lid |
| Ventilation | Lid props open -- manual, and it matters |
| Footprint | Sits on a bed or on the ground |
| Assembly | Minimal |
A first real greenhouse
Palram Canopia Mythos Greenhouse
Palram Canopia
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The sensible first greenhouse: an aluminum frame with twin-wall panels, sized to fit a normal backyard rather than a nursery.
Twin-wall polycarbonate is the thing that separates a greenhouse from a plastic tent. Two skins with an air gap between them insulate, and the panel diffuses light rather than throwing hard shadows, which suits seedlings better than clear glass does.
The Mythos sits at the point in the range where you get a proper aluminum frame, a roof vent and a lockable door without paying for the heavy-duty glazing. For starting seeds, hardening off, and stretching the tomato season at both ends, that is the right specification.
Two warnings from the manual that people ignore. Anchor it -- every lightweight greenhouse that ends up in a neighbor's yard was not anchored. And build it with a second person; the panels flex and the frame is not square until the last bolt.
What works
- Twin-wall panels diffuse light and insulate better than single-skin plastic
- Aluminum frame will not rust or need painting
- Lengths let you match the run to the space you have
- Roof vent included rather than sold as an extra
What does not
- 4 mm glazing is thin for real winter use
- Assembly is a long afternoon and genuinely needs two people
- Must be anchored -- an unanchored kit is a sail
Skip it if: you live somewhere with heavy snow load. 4 mm panels are a three-season specification; the thicker-glazed models exist for a reason.
| Frame | Rust-resistant aluminum |
|---|---|
| Glazing | 4 mm twin-wall polycarbonate |
| Sizes | 6 ft wide, several lengths including 6 x 8 and 6 x 10 |
| Ventilation | Roof vent, lockable door handle |
| Base | Integrated base rail, anchoring required |
Knowing what actually happened overnight
Min/Max Greenhouse Thermometer
Various
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The cheapest accessory that changes decisions: it tells you the overnight low and the midday high, not the temperature at the moment you happened to look.
Every greenhouse decision -- when to sow, when to vent, whether you need a heater, whether the frost cloth is doing anything -- depends on a number most owners never measure: the overnight low inside the structure.
A min/max thermometer records the high and low since you last reset it, so a morning glance tells you what happened while you slept. That turns guessing into knowing, for the price of a bag of compost.
Hang it at plant height and out of direct sun. A thermometer in a sunbeam reports the sunbeam, not the greenhouse.
What works
- Shows the overnight low, which is the number that kills plants
- Cheap enough to put one in the greenhouse and one in the cold frame
- Tells you whether venting is working
- No installation
What does not
- Reads wrong if hung in direct sun
- Digital versions need a battery
- It measures, it does not fix anything
Skip it if: nothing. If you own a greenhouse and not one of these, you are guessing about the only variable that matters.
| Type | Min/max recording thermometer |
|---|---|
| Reading | Current, plus high and low since reset |
| Mounting | Hangs at plant height, out of direct sun |
| Power | Digital models take a single cell |
Common questions
Is a cold frame as good as a greenhouse?
For hardening off, early sowing and overwintering hardy greens, a cold frame does the same job for a fraction of the cost. It cannot grow crops to maturity under cover, and you cannot work in it in bad weather -- those are what a greenhouse is for.
Should I buy a cold frame before a greenhouse?
If budget is the constraint, yes. It is the cheaper experiment and it tells you whether you will actually use protected growing before you commit to a structure with a base, anchoring and a permanent footprint.
Can you use a cold frame and a greenhouse together?
That is the common end state. The greenhouse raises seedlings and grows tall crops to maturity; the cold frames sit directly on the beds and handle hardening off and winter greens where the plants already are.
Does a cold frame need heating?
No -- a cold frame uses only the sun, which is where the name comes from. A hotbed is the heated version, traditionally warmed by decomposing manure beneath the growing area. For most gardens, the unheated frame does everything needed.
Sources
Factual claims on this page are backed by the published sources below, and product specifications are the manufacturers’ own. Where a figure is not published, we say so rather than estimating it.