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Vegetables. When is too soon, too soon?

In the ever-changing climate of Idaho (and often times, quite rapidly), it can be difficult to know when it's actually time to start those seeds you've been dying to plant since last fall!

General rule of thumb for Idaho is mid-March to put your nubile plants into the dirt. But when should you start growing them so they're ready by March 15?

Short answer: NOW!

As long as you start your veggie seeds INDOORS to protect them from any frosty mornings we may still have. I highly recommend placing them in solo cups or jiffy pots (although those can get really expensive). Simply fill a cup with dirt, place the seed about an inch below the surface, water daily. Ezpz! Be sure to put them in a windowsill or other sunny spot where the shoots can absorb what sunlight filters in through the window. Conversely, you can also place them under a grow light, but you MUST make sure you turn it off at night. Plant's "daylight" cycles need to be as close as possible to the natural hours of daylight a plant would receive if planted during the growing season.

How much light? I'm glad you asked. Let's first go over a few common vegetable seeds.

Since seeds vary in what type of weather they thrive in, you will not be planting, say, sweet corn, just yet. Peas, green beans, broccoli, cabbage, edamame, carrots, spinach, kale, lettuce, cauliflower, potatoes, cucumbers, squashes, asparagus, and pumpkins are all examples of cool weather vegetables. If you are late in planting these guys, you can try again in early fall. This is because these specific plants do not flower or produce very well in hotter temperatures. They go dormant, and slow down on production (that's not to say you WON'T get any harvest by planting these guys late, it just won't be as good).

Temperatures below 32 degrees will frostbite and kill your vulnerable little guys you worked so hard to baby to the size they need to be planted. If the temp drop is only temporary (track the weather on your phone via an app, or simply watch the morning news to get hip to the temperature situation), there are a few options you can pick from to TEMPORARILY protect your little guys, but these are NOT long-term solutions to limp your way through a healthy crop all winter. Your plants roots must not be allowed to freeze. This will cause all kinds of problems, including root damage, leaf damage, and fruit damage as well, stunted growth, and other unwanted issues.

You may find that sometimes, the temps will dip below 40 degrees, even in the warmer spring months. Here's a few ideas to get your plants through those unexpected cold snaps:

Use Mulch

Mulch is an organic material you lay on 1-2 inches thick on the surface of the soil. Examples include grass clippings, dried leaves, straw, or wood chips. The mulch creates a barrier of insulation for the soil. This means the temperature in the soil does not change as drastically when the outside temps fluctuate.

Heat Sink

Another option is called a Heat Sink. It will absorb heat from the sun during the day and radiate it to your plants at night when the temps get cooler. Create a Heat Sink by placing a dozen 1-gallon containers in your garden and plant your plants directly in them. This provides several benefits. First is (of course) protecting your veggies from cold snaps by making them transportable into your home if you can drag them all inside at night when the forecast is nippy. Container gardening is also good for containing your vegetables, and preventing a mess of branches, tubers, and general wildness of the plant. No messy clean up. Just dump the dirt back into your garden area and toss the dead plant at the end of the season.

If you DO decide to take the Container method for your garden, please, drill drainage holes in the bottom of your buckets. Otherwise, when you water, that water sits at the bottom of the bucket and rots, molds, and becomes gross and stagnant, inviting pests and diseases into your vegetable soil. Nobody wants little bugs flying about because of mildew.

Row Cover

The easiest temporary protection is a row cover. This works best with mature plants that have at least 2 months of growing time (ish) under their belts. Landscape fabric, Visqueen, frost cloth, bed sheets (we all have at least 3 flat sheets that don't go to any set of linens in the closet), straw, or newspaper.

When using this method of frost control, DO NOT allow the row cover to come into contact with ANY portion of the plant, as it will conduct cold TO them, not away from them. Use bamboo sticks or stakes as support to create a tent with the row cover on top and the plants at the bottom.


Cloches are containers you place over the plants. Works great for seedlings that aren't quite old enough for the row cover. Also, one of the most expensive options, as they are a specialty greenhouse item. However, as a very temporary measure, you can cut a water bottle in half, and place that over your seedling to protect it.

Now, let's move onto WHEN to plant.

What temperatures are too cold for vegetables?

I’ve added a list below of some of the vegetables and the temperatures that would be too cold for them to survive.

Vegetable Lowest temperature (Fahrenheit):

Tomatoes: 32

Beans: 31

Broccoli: 29

Carrots: 28

Cucumbers: 30

Kale: 27

Potatoes: 28

Radishes: 30

Spinach: 30

Squash: 30

Corn: 32

Beets: 29

Cabbage: 26

Cauliflower: 27

Okra: 29

Pumpkin: 31

Asparagus: 30

What are some frost-tolerant vegetables?

If you grow some of these frost-tolerant vegetables, you will not have to worry about a drop in the temperature because they plants have no issues with it.

  • Lettuce

  • Carrots

  • Spinach

  • Turnips

  • Collard

  • Swiss chard

  • Parsnips

  • Broccoli

  • Kale

  • Leeks

  • Brussels sprouts

How can I tell if my seeds were damaged by cold?

If you have planted seeds in your vegetable garden and it was hit by a temporary drop in temperature, you need to check the condition of your seeds.

If you find that the seeds have not germinated even after a couple of weeks, you can dig into the soil and check their condition. If the seeds have turned black and soggy, they’re dead and you will need to re-plant new ones.

If the seeds are healthy, I would suggest waiting for a couple of weeks and allow the seeds to germinate. Some of the seeds may go dormant due to the drop in temperature but they will bounce back as the temperature returns to normal.

If you find that the seeds are not germinating even after a couple of weeks, you can move them indoors in a seed-starting tray.

I would recommend you start seeds indoors, if you can for some of the plants. This will give you a good germination rate as the seedling will be protected from the cold.

Final thoughts...

Really, it's about being smart and knowing cold can kill your plants. Do your homework on when the temperatures generally start reaching the 40's AT NIGHT. Not your "high temperature" forecast for that day. You want to look at what the "Low overnight temperature" is going to be and decide when to begin planting. Direct sowing is much different than starting seedlings and is a much more streamlined process compared to container starts. The downside to that, is you may get a shorter season of production, due to unforeseen cold.

If you aren't worried about direct sowing and want to do container seedlings and THEN direct sow, definitely wait until mid- to end- of March to put them in your garden area. We may still have a bit of frosty conditions at that time, but you now have a few good resources to mitigate those damages that the frost can cause.


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