What to Do Before the First Frost: Oct. 3–4 Checklist

You are not the only one when your weather app is telling you that the temperature will drop to about 31 o C on Saturday-night. Your tomatoes are full, the basil is gigantic and the porch geraniums have at last come out. Panic not, and do not hurl a bedsheet over all at midnight. This is the checklist that will take you step by step on what to harvest, cover, and bring home this weekend to ensure that Sunday morning is black with leaves.

Quick Answer: Before a cold night, water the soil, harvest tender crops, move potted tropicals inside and cover all other items with breathable material before the sun sets. A light frost only slightly kills delicate plants whereas a hard freeze kills most of the garden. Uncover the next morning when the air is over 32C.

Frost v. Freeze: the Difference and Why It Matters.

These two words are used interchangeably by people, yet they refer to different weather and your plants respond differently to each.

A frost is an ice on the surface, although air a few feet below it is still over 32 F. on a clear, calm night the leaves may radiate heat to the sky and actually be several degrees colder than the thermometer on your porch. An advisory is normally issued by the National Weather Service when lows are anticipated to be around 3336F in the growing season (Source: National Weather Service).

Frost is more inclined when the skies are clear and the air is still and clouds and wind prevent heat to escape. This is why that 36 f forecast can snatch your basil on a calm starry night but not a day when it is a breeze and cloudy (Source: National Weather Service).

Freeze denotes the decrease in air temperature to 32 F or less. By that time ice may develop inside the leaves and stems and burst open plant cells to leave the tissue mushy and black (Source: university cooperative Extension).

The three levels are as follows:

The conclusion: frost endangers your most delicate plants, a freeze endangers almost everything.

What Temperature Is Too Cold for Plants?

It does not have a magic number, since plants can be categorized into cold-tolerance groups. Take 32 F as the temperature at which tender plants begin to suffer, and 28 F as the temperature at which the larger part of the garden begins to suffer. The same groupings are published by university extension programs across the country (Source: university cooperative extension).

Those numbers can be changed by two things. The former is length of time: a brief down to 31 F dawn has little to do with half a day of below zero. The second, is location: plants next to a south-facing wall or under the shade of a tree may be several degrees warmer than those in an open yard, and the low areas trap cold air like a bathtub full of water.

Wish to know what your garden struck? The actual low at night is indicated by a low-cost min/max thermometer at the base of the plant. The readings tend to vary with the closest weather station by a number of degrees.

Skip your USDA hardiness zone when making tonight's call. The map is an average of the lowest temperatures of coldest winter, not a one-time spike at the beginning of the season (Source: USDA Plant Hardiness Zone Map).

In most of the northern half of the nation, the mean first fall freeze, on average, comes between late September and late October, and thus an early October cold wave is not uncommon (Source: NOAA National Centers for Environmental Information). This week prediction can be compared with the climate normals of your locality as given by NOAA.

Frost Advisory Tonight? Your 7-Step Emergency Plan

Work according to this order, whether you have two days or two hours. Covers are effective when they confine the heat that the soil had stored during the day and therefore time is always of the essence.

1. Test your low. Not just a generic phone widget, but the National Weather Service forecast of your ZIP code, and record the hour the temperature bottoms out.
2. Water the ground by mid afternoon. Damp soil stores and gives out more heat at night than dry soil (Source: university cooperative extension). Sprinkle the bottom of plants, not the leaf.
3. Harvest what's ready. Select ripe and almost ripe tomatoes, peppers, squash, and herbs. Details are in the harvest section below.
4. Transport pots and baskets. Whatever is in a container can be carried around the house, into the garage or inside.
5. Collect sheets and cushions. Take bed sheds and burlap or row cover and stakes, hoops or tomato cages to prevent cloth over the leaves.
6. Cover plants an hour or two before sunset. Cover the floor completely with drape fabric and balance the edges with bricks, rocks or landscape staples.
7. Discover in the morning. Uncovered when the sun reaches the bed and the air is above freezing to ensure that plants do not overheat or remain damp.

Short on time? Cover tomatoes, peppers and basil initially, then relocate pots. All the others can withstand a light chill.

The plan will match a Saturday night low as follows:

Pro tip: When your predicted minimum is 32-34°F, a single light layer will do. When below 28o F, cover up twofold and place some jugs of water beneath your covers

How to Protect Plants From Frost: Covers, Water, and Heat Tricks

What you cover your plants with is more important than you think it is to some gardeners. The improper material may trap the water or direct the cold directly to the leaves. The most typical ones are listed here.

Any cover work is improved by four rules:

• Keep cloth off the foliage with supports, cages or hoops, since cloth that comes into contact with foliage may conduct cold directly.
• Cover and peg on the edges to ensure that warm air trapped in the soil remains trapped.
• Plastic will have to be skipped unless you can prop it up and vent it the following day.
• Roots should be mulched with 2-3 inches of straw, or shredded leaves, though, bear in mind the mulch covers roots, not leaves above.

No hoops? Bend 1/2-inch PVC pipe or flexible wire in arches over a bed, or surround a plant with a ring of tomato cages and cover top with fabric. The cover is fastened on hoops with clothespins or binder clips in a breeze.

The incandescent string lights that are old fashioned and hidden under a cover provide a bit of warmth, whereas LED strands produce nearly none. Take outdoor-rated extension cords and do not place bulbs in contact with fabric.

Bring Plants Inside Before Frost: What Moves and What Stays

The lowest cold-tolerant of any thing that you grow is house plants and potted tender plants. Night temperatures lowering below 50 degrees Fahrenheit start to cripple many of the tropical types, long before the onset of freezing (Source: university cooperative extension). When you are predicting that you could be in the low 30s, you must already be getting those plants shipped in.

A rule of thumb: once nighttime temperatures are in the 50s, begin transporting tropicals a batch at a time. Leaving it to the last moment is to carry big pots in the dark, and there is no time to look to see whether there are bugs.

Move these indoors:

• Plants that were kept outside in summer, such as pothos, monstera, ficus and snake plants, are tropical houseplants.
• Container plants like hibiscus, mandevillas, begonias and geraniums are tender.

• Potted basil and other delicate herbs
• Succulents and cacti, which rot soon in cold, wet weather.

Keep all these out of the way:

• Hardy mums, pansies, ornamental kale, hostas and sedum. Place the pots together on the house to provide additional protection.

Get rid of pests in your living room:

1. Wash leaves, such as the underside, with a fine spray of water.
2. Check stems and soil of aphids, spider mites, scale, and fungus gnats.
3. Treat insecticidal soap issues, as directed.
4. Two weeks of quarantine of new arrivals in a separate room.
5. Keep them in your sunniest window, and have some leaf drop, as they adapt themselves to less light.

To do a room by room walkthrough, see our houseplant move-in guide.

What to Harvest Before a Freeze and What to Do Afterward

Harvest Now or Let It Ride?

The tender crops are first as they will not withstand a freeze. Durable crops can remain in place.

Pick now:

• Basil that blackens, cut all stems.
• Tomatoes, ripe and those that are green at the same time with a pale, whitish-green glow that will ripen at room temperature indoors.
• Green beans, cucumbers, summer squash, and peppers and eggplant.
• Pumpkins and winter squash, with some inches of stem.

Place tomatoes in a single layer in a cool dark place, and check tomatoes every couple of days.

Rolling: kale, collards, spinach, Brussels sprouts, carrots, beets, parsnips, leeks, and cabbage. Most of them are sweetened after cold temperatures due to conversion of starches to sugars to help plants endure cold conditions (Source: university cooperative extension).

Hanging to a favorite pepper plant? Get to know how to store your pepper plants at home through the winter rather than letting such an expensive variety go to waste.

The Morning After

• The discoverer gets out when the sun is on the bed and the air above freezing, which is generally in mid-morning.
• Delay a day or two in evaluating damage. Frozen tissue indicates blackened and mushy leaves, whereas a light nip usually rings.
• Hold off pruning damaged perennials and shrubs. The dead growth protects the plant, and pruning now can cause new tender growth, which will be killed by the next frosty night (Source: university cooperative Extension).
• Pull removed annuals and composted the healthy ones. Dispose of tomato vines with a disease.
• Change to fall planting. It is also best to plant garlic in cool soil and spring bulbs are planted in the coming weeks. When the squirrels have dug up your beds, begin with squirrel-proof bulbs.

References:

• National Weather Service (NOAA): frost advisory and freeze warning criteria, and the weather conditions that favor frost (clear, calm nights).
• Land-grant university cooperative extension programs: (for example, University of Minnesota Extension and Colorado State University Extension): effects of freezing on plant tissue, cold-tolerance groupings, soil moisture and heat retention, row-cover performance, houseplant chilling thresholds, cold-sweetened crops, and delaying pruning of frost-damaged plants.
• USDA Plant Hardiness Zone Map (USDA Agricultural Research Service and Oregon State University PRISM Climate Group): what hardiness zones represent.
• NOAA National Centers for Environmental Information: average first fall freeze timing and climate normals.

The Bottom Line: Protect What Matters Most

You do not have to save all the plants, only those that you would miss. Water the earth, harvest the soft material, carry the containers in the house, and cover the others before the sun goes down, and uncover them after the sun heats things. Then read how mulching fallen leaves into your lawn nourishes the soil all winter, then browse our seasonal gardening guides to know what to plant, protect, and prepare before the real winter comes.