Season-extension fabrics, hoops, and what each one buys
Row-cover weights, frost blankets, and plastic tunnels for the high West, with CSU's temperature notes and a way to price the roll.
The question at the garden center is which roll to take home, not whether covers “help.” Colorado State University’s frost-protection note says floating row covers can provide up to about 10°F of protection, and that the amount depends on the material and the grade.
The mountain vegetable fact sheet is narrower and more useful at elevation: lightweight spun-polyester row cover can protect down to 24°F depending on thickness, lets sun and rain through, and does not need to be vented. A frost blanket, heavier, extends a mountain season a week or two further at each end.
Plastic on hoops can add about a month at each end, and wind or an early snow will wreck it if you are greedy with the dates. Insect cloth that does not state a temperature is a bug net. Do not assign it the 24°F rating.
What to buy for which crop
Use the mountain sheet’s split. Greens, brassicas, peas, and other crops that do not need an insect to set fruit can live under a floating cover for the stretch you are stealing.
Summer squash has to come out from under the cloth at flowering or it will not set. Beans and peas are self-fertile, and the shorter varieties will grow under the cover. That is why a mountain salad bed can stay covered and a zucchini bed cannot.
A Front Range tomato in May wants the heavier blanket on the nights that still reach the late-frost column, then the blanket off when the sun is on it. Leaving a frost blanket on for a month yellows the plant. The row cover page is the nightly habit. This page is the shopping list.
Plastic low tunnels, in the same fact sheet, are hoops of half-inch PVC, electrical conduit, or 6- or 9-gauge wire, with sturdy plastic pulled tight, sandbags or rocks on the sides, and the ends staked. UV-stabilized greenhouse film lasts more seasons than untreated plastic and costs more. Vent every mild day. A closed tunnel on a 70°F April afternoon at 5,280 feet is an oven.
A bill of materials for one 4-by-12 bed
Price the tags yourself. The quantities are the part that does not change when the store does.
| Piece | Quantity for a 4-by-12 bed | Why it is on the list |
|---|---|---|
| Medium or heavy row cover, wide enough to reach the ground on both sides | One piece at least 10 feet wide and 20 feet long | The extra width is the edge you bury or weight. A cover cut to the bed width will not stay. |
| Hoops: 9-gauge wire, or half-inch conduit | One hoop every 3 to 4 feet, so four or five | CSU notes that hoops keep fabric off the leaves. Sagging fabric freezes to the crop. |
| Garden staples, or rebar pins, plus sandbags or logs | Enough for every edge, not two decorative rocks | The mountain sheet names staples, rebar, logs, or heavy rocks because spring wind takes a loose cover. |
| Frost blanket, separate from the insect cover | One piece the same footprint, stored dry | You add it on the cold night. You do not leave it on as the summer roof. |
| Optional clear UV film | Same hoop set, only if you will vent | The month-at-each-end claim is for this, not for insect cloth. |
A second bed does not need a second philosophy. It needs another cut of the same cloth. Buy the widest roll you can store. Patching two narrow remnants down the middle is how the wind finds a seam.
How the money actually goes
Soil and lumber for the bed itself are a different receipt, on the raised-bed materials page. The cover is usually the smaller check, and it is the one that fails by being the wrong product.
People buy a cheap insect veil, watch a 28°F night burn the lettuce, and decide covers do not work. The fact sheet’s 24°F figure is for the thickness that earns it. Ask, or read the package. If the package only says “garden fabric,” put it back.
Hoops outlast fabric. Conduit costs more than wire and survives a wet snow better.
Wire is enough for a row of spinach. A cattle panel bent over the bed is the hail roof, not the frost blanket. That build is on the hail and fence materials page.
You can clip frost fabric to the same panel on a cold night and take it off in the morning.
Do not leave plastic on a cattle panel through a May afternoon unless the ends are open.
Walls of water, the water-filled teepees, are a single-plant tool. They make sense for one or two tomatoes on the Front Range through the late-frost date. They are a poor way to cover a 12-foot row, and they blow over if you do not stake them.
A cold frame is the rigid cousin for a salad patch you will vent. Compare the two on the frame and greenhouse page before you buy a kit with a window you cannot lift.
What not to spend on
Skip a roll that is too narrow. Skip black plastic as a season extender. It is a soil warmer and a weed barrier, and it does not protect leaves from a frost.
Skip a patio shade cloth labeled only in percent shade and expect it to stop hail or a freeze. Hail cloth and frost blanket are different weaves. The hail page keeps them apart.
Do not buy enough fabric to wrap the whole yard. Cover the salad bed, the berry row, and the tomatoes you cannot stand to lose. Potatoes under the soil do not need a roof for the tubers’ sake. A $0 decision is leaving the buffalo grass outside.
Store the cloth dry. Dirt abrades it. A hose-down is fine if it dries before it goes into the shed.
Mice nest in a wadded wet blanket. Fold it.
The mountain sheet’s promise of a couple of weeks, or a month under plastic, assumes the cover is actually on the bed when the night arrives, not in a crate behind the snowblower.
Checklist
- Match the product to CSU’s split: floating cover, frost blanket, or vented plastic. Do not guess the degrees.
- Cut the fabric wide enough to weight the edges.
- Hoop it if the cloth would lie on the leaves on a freezing night.
- Uncover squash at flowering. Leave self-fertile short beans covered if you want.
- Pin for wind. The Front Range will test this in April.
- Price the roll locally. The quantity above is the list. The tag is the cost.
- Keep the blanket for nights and the hail cloth for the summer roof.
The dates that tell you when the cover has to be ready are on the calendar for your station, not on the fabric package.
Sources
- CSU Extension, Frost Protection and Extending the Growing Season.
- CSU Extension, Vegetable Gardening in the Mountains.
- CSU Extension, Colorado Vegetable Guide, on covers running warmer than open air and on hail.