Crops that came from warmer parts of the world cannot tolerate even a light frost, and may even begin to suffer at temperatures below 50 degrees Fahrenheit. Basil is an extreme example of this, as the leaves can turn black when the temperatures dip into the 40s.
"The ground temperature is still pretty warm so when you do cover your plants the heat from the ground actually helps protect them as well," Ewing said. When it comes to what flowers or plants could be in jeopardy, it varies. "Your topicals, they're not going to like it below 50.
Most houseplants are tropical plants that can safely grow in a heated home during the winter. They will never survive outdoors in winter unless you live where the temperature stays at least above 50 degrees. In northern zones 4 and 5, plants need to survive months of below freezing weather every winter.
Freeze Warning - This is issued when there is at least an 80% chance that the temperature will hit 32 degrees Fahrenheit or lower. Light freeze - 29° to 32° Fahrenheit will kill tender plants.
Cover Plants – Protect plants from all but the hardest freeze (28°F for five hours) by covering them with sheets, towels, blankets, cardboard or a tarp. You can also invert baskets, coolers or any container with a solid bottom over plants. Cover plants before dark to trap warmer air.
Each plant has a different threshold when it comes to dealing with the cold. Some plants can survive outside even when temperatures hit freezing. Others need to be brought indoors when temperatures reach the mid-40s. Be sure you know this before you plant.
Pipes can freeze whenever the temperature is below 32 degrees Fahrenheit. Insulated pipes are most likely to freeze at 20 degrees or colder. Drip or cover faucets when it's 28 degrees or colder for three or more hours.
A light freeze (between 32 and 29 degrees F) can kill tender plants. A moderate freeze/hard freeze (between 28 and 25 degrees F), can cause wide destruction to most plants. A severe freeze/killing freeze (24 degrees F and below), causes heavy damage to most plants.
When temperatures are above 40°F, check soil moisture and water if needed (be sure to avoid over-watering). When temperatures are consistently warm in fall and winter, take advantage and keep the plants hydrated.
WHEN TO BRING PLANTS INSIDE. As a general rule, tender plants should be brought in when nighttime temperatures are below 50 to 55 degrees F, even if they are hardy for your zone. A plant's roots are more exposed when planted in a container versus in the ground.
Another temperature to keep in mind: tomato plants will not survive in temperatures below 35 degrees Fahrenheit, and will not thrive at temperatures below 50 degrees. Gardeners can use a frost date calendar to note their region's average dates of last frost in spring and first frost in fall.
When do I know it's safe to bring my plant outside? It's safe to move your plants outside when the outdoor temperatures stay consistently above 50°F. Pay attention to the weather report. If nighttime temperatures are set to fall below 50°F, bring your plants in for the night.
Plants native to the subtropics are in danger below 40 degrees F and pretty certainly going to be killed at 32 degrees F. Plants native to the tropics are often damaged below 50 degrees F and perish at about 40 degrees F.
In general, foliage plants grow best between 70 degrees and 80 degrees F. during the day and between 60 degrees to 68 degrees F. at night. Most flowering plants prefer the same daytime temperature range, but grow best when nighttime temperatures range from 55 degrees to 60 degrees F.
In fact, you can leave plants covered with blankets or sheets for several days without harming them if freezes are likely for several nights in a row. But eventually the covers must be removed so the plants can get light.
First, it's good to know which plants are sensitive to temps around 35 or 40 degrees F. These are common tender plants that will need some protection. Hanging baskets: begonias, calibrachoa, gerbera, impatiens, vinca, euphorbia, and scoparia.
Morning watering is actually preferable to evening watering as the plant has time to dry before the sun goes down. At night, water tends to rest in the soil, around the roots, and on the foliage, which encourages rot, fungal growth, and insects.
Many indoor plants will see damage when temperatures drop to the mid to lower 40s°F and nearly all will die if exposed to below freezing temperatures. Watch the weather forecast and bring plants back indoors well before nighttime temperatures get too cold. Before bringing them inside, check for insects.
Plants need to be transitioned indoors before the outside temperature starts dropping below 45 degrees Fahrenheit (7 degrees Celsius) at night. If it's a tropical plant, such as a potted lemon tree or passion flower, you'll want to start the transition before temperatures hit 50 degrees F (10 degrees C) at night.
Covering plant material at temperatures between 39-30 with freeze cloth or covering can be effective. Prolonged exposure at temperatures of 28 degrees and below will notice protection results diminish with each degree dropped.
Damage is More LIkely When in Bud or Bloom
Overall, even flowers can tolerate light freezes (low 30s to upper 20s °F) and even a little snow. Record cold temperatures (below mid to upper 20s) will damage or destroy many of the flowers of early blooming varieties.
A light frost may cause minimal damage while a severe frost may kill plants. Young, vulnerable plants are much more susceptible to a light freeze, which occurs when temperatures are 29 to 32 degrees Fahrenheit, while mature plants may only suffer from short-term effects.
If you do not want to spend extra money on a high water bill, or you are able to isolate your exterior faucet from the mains water supply, then covering the faucet will likely be better for you. If you can drip your faucet, however, then it may be more effective in protecting your pipework from over-expansion.
Typically, outdoor faucets should be opened when temperatures fall below 20 degrees Fahrenheit. Freezing water expands and can cause pipes to crack or burst. If you have a frost-free faucet, it provides extra protection, but you may still need to leave it open during extreme cold.
Exterior pipes should be wrapped with insulation tubing, which can be found at your local hardware store. Do not wrap your pipes with bath towels or newspaper! These coverings hold moisture like a wet rag and defeat the purpose of covering your pipes in the first place.