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What Is a Late Frost?
If you plant too early, you need to know how to protect your tomatoes, peppers, and eggplant from the cold, just in case a late frost is headed your way. But what is a late frost? It simply refers to a frost that arrives later than the typical last frost for your area.
Unlike many cool-season crops like peas, lettuce, or broccoli that do just fine with one more last frost, warm-season stars that include tomatoes, peppers, and eggplant do not appreciate frost at all. In fact, a frost of any significance could easily kill them and leave you running to the nursery for more. Instead of taking that chance, be ready just in case old man winter has one more trick up his sleeve.
When to Plant Warm-Season Crops
The first thing that you should do to protect warm-season crops from getting bit by frost is to avoid planting them too early. That means that these plants should not be outside until after the average last frost for your hardiness zone unless you have reviewed the extended weather forecast and determined that you are in the clear.
To easily see your town's average last frost, check out the plantmaps site, where you can search by zip code to easily retrieve this information.
Now, to be safe, plant tomatoes no earlier than this date. Peppers and eggplant are even stingier and will appreciate another week or two. While they can be planted after danger of frost has passed, they really grow best in heat and won't do much when days and nights are still very cool.
If you are starting these plants from seed, try to time the sowing with your last frost date as well so that the seedlings are just the right size when it's time to put them out in the garden. Start eggplant and peppers about 8 weeks ahead of the last frost date and tomatoes six to eight weeks early.
Here is a summary to make it easy to see:
|Vegetable||Sow Seeds Indoors||Plant Outdoors|
8 weeks before last frost
2 weeks after last frost
8 weeks before last frost
0–2 weeks after last frost
6–8 weeks before last frost
last frost date
Protecting Plants From Frost
If the planting is done and a frost is on the way, don't despair. There are steps that can be taken to protect vegetables from frost and keep them happy. None are as easy as waiting until the signs of frost are over, but all are simple enough.
Floating Row Cover to Protect From Frost
The easiest method of protecting plants from a quick frost is to use a floating row cover. These are typically some type of polypropylene fabric that breath but protect plants underneath from coming into contact with frost. Floating row covers can easily be found at a nursery or online garden or seed retailer, and a nice roll of this fabric is a great addition to any garden shed.
Cover Plants With Fabric
There are really two ways that you can use a row cover. One is to simply cover the plants with the fabric, which will work well enough for a light frost on a single night, where you go out and remove it the next day.
Use "Hoops" to Elevate and Drape Cloth Over Plants
The other way, which is more permanent, is to use "hoops" to elevate the cloth above the plants and then drape it over the hoops. These can be made with any bendable material, but simple PVC piping from the hardware store is very common since it is waterproof, inexpensive, and easy to bend.
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To make this type of structure, just install a hoop every few feet and then set the cloth over them. If frost persists for more than one night, this setup will allow you to leave it in place until the warmth comes back.
When using a floating row cover, be sure to fix it in place somehow. Some gardeners press landscape staples through the edges of the fabric into the ground, while others prefer a few smartly placed rocks to prevent the wind from whipping the fabric away. Any method that will keep it from blowing off the plants will work fine.
Wall-O-Water for Tomatoes, Peppers, and Eggplant
There is a product called Wall-O-Water that works very well for frost protection of single plants. This is a very simple tool to use but not practical for a large garden with a whole bunch of warm-season vegetables that need to be protected. Still, if you have a few prized plants or a small garden, this is worth a look.
The Wall-O-Water is filled with water and placed around the young plant. As the temperature falls during the night, the plant is protected inside this wall with temperatures that exceed those found outside of it. They are reusable for years and really do a nice job.
For frost protection on a small scale, or even if you want to plant tomatoes or peppers before the average last frost, the Wall-O-Water is a great choice.
Protecting Plants From Early Fall Frost
There are some years where an early killing frost shows up that will threaten your prized peppers, tomatoes, or eggplant. In this case, the row cover will still work, but the problem is that now your plants are very large.
In fall, a simple bed sheet may be a better choice. It is light but big and will cover big tomato plants. Just be sure to drape it over the plants loosely and get it off as soon as possible the next day. A sheet that actually gets wet can still kill your annual plants.
Another reasonable option is to harvest. Tomatoes will continue to ripen on your kitchen counter for several days after being picked. If a fall frost happens when the days are getting rather short anyway, the productivity of tomatoes outdoors will continue to decline. Perhaps now is the time for freezing and canning what's left.
Peppers will also ripen to some degree. Many gardeners like to pick all the remaining peppers in fall and put them in a cardboard box to ripen. Many peppers that turn color will continue to color in this way. They don't have the same shelf life as tomatoes, however, so watch over them and pull out the ripe ones each day until you have eaten them all up.
When it comes to eggplant, picking early to ripen indoors probably won't make you happy. These purple vegetables are best eaten when freshly picked from the garden.
Tips for Savings Plants From Frost
Let's do a quick review. To keep warm-season vegetables like tomatoes, peppers, and eggplant from succumbing to a frost, try these methods:
- Plant after danger of frost has passed.
- Time seed starting so that plants get set up at the right time.
- Use a floating row cover.
- Try the Wall-O-Water.
Even if you are patient, some year the frost will come when it's not expected. If you are prepared to act when needed, you can save your tomatoes from frost—and your eggplant and peppers too.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2013 landocheese