Is it Warm Enough for My Veggies?

The May long weekend is coming! This is the traditional weekend for getting everything in the garden. 

I think that many gardeners still tend to lump all vegetables into one category when it comes to temperatures. The prevailing sentiment is that cold and frost is devastating for all varieties of vegetables. But nothing could be further from the truth. 


Vegetables are truly individuals and they run the spectrum when it comes to ideal and injurious temperatures. To illustrate this point, I’ve included my vegetable/temperature chart.

The temperatures in the chart list the baseline temperatures that plants require to grow. For example, eggplant essentially stops growing at 15.6 celsius while at the other end of the spectrum, onions will grow at temperatures above a chilly 1.7 celsius! Onions can also tolerate several degrees of frost without sustaining damage. 

The ‘heat unit’ component of the chart is particularly important for commercial growers especially in our region. For example, different varieties of sweet corn will require varying amounts of heat to develop mature cobs. Growers look at the average high temperatures and average low temperatures, for their region, then calculate the average heat units. If the calculation shows that they are growing in a ‘2200 corn heat units’ zone, then they would be pretty safe growing 2200 heat unit corn varieties. 2800 heat unit corn varieties would be very risky and likely not mature before the first fall frost.

So if you follow the chart data, you can pretty much plant all of your vegetables, but you may want to hold-off on the eggplant and okra for a few more days. 

– Jim Hole