The Madman Watches The Temperature

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We are rapidly approaching the last frost date. In fact, it’s tomorrow if you listen to the madman. May 15 is the start of our frost-free season – no temperature below 32°. We have all spent the winter getting ready for this. Time to grow!

The madman walking along a row next to pea plants — *Our peas love this cool weather.*

Some of us are already growing things. The cool weather crops have been in the ground for a while. Crops like peas, onions and broccoli prefer to get their start in the cool weather. Often called cold weather crops, they don’t actually prefer the cold – they just tolerate it. In reality, their favorite temperatures hover around 50˚-65°. If it gets too cold, they survive, but don’t flourish. And if it gets too hot, they just bolt.

Summer Vegetables

But, May 15 signals the start of the season for warm weather crops. Things like tomatoes, peppers, flowers, herbs. And these are the crops we want to talk about, because when you mention garden, everyone imagines the lush vegetables we can pluck from the plant and pop in our mouths.

Remember May 15 is just a date. And, in this case it is the date of the average last frost, based on historical data. It doesn’t mean that it won’t frost after this date, just that it probably won’t. Do you remember last year? The madman certainly does. Right after the fifteenth, we had a couple of days of record low temperatures. Lots of tender vegetable plants died in that cold snap because the last frost date was actually on May 17.

Watch The Weather

A good look at the 10-day forecast by some overzealous gardeners may have saved a lot of plants. So, the madman has been studying the 10-day for about 2 weeks now. Before that, he worried over the soil temperature (no planting until it hits 70˚ consistently).

tomato leaf with brown blemishes from the temperature — *Cold weather damage on a tomato leaf. Photo by Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org.*

As of today, it appears that the coldest temperatures are behind us. And there is no frost on the horizon. But our overnight lows are only in the 50˚s at best. These temperatures keep cool weather crops happy but may not be the best for plants like tomatoes and peppers. The madman is holding off putting these warm weather crops in the ground for at least another week.

Done With Frost

It’s unlikely that temperatures will drop much into the 40˚ range, but this is New England, and the madman has learned to be careful. Besides, he knows that cooler overnight temperatures can stunt the plants’ growth. Of course, you all know he’s always looking for the perfect growing conditions – daytime temperatures in the 80˚s and nighttime temperatures in the 60˚s. But as I just said this is New England – these conditions are rare. So, we play the waiting game.

flats of transplants on a table outside the greenhouse — *The madman’s transplants are getting used to being outdoors.*

We aren’t really waiting; we are getting everything ready for the big planting day. Remember, before going into the ground, transplants need to be hardened off. Every day, the madman moves his plants from the greenhouse to the outdoors – slowly getting them adapted to life outside. They need to adjust to direct sunlight so the leaves don’t burn outside. They also need to get stronger. While they adjust to the sun, the gentle breezes are strengthening their stems. For us, the hardening off process takes about 10 days. Each day, the madman adds a little more time to the plants’ outside exposure. He makes sure they are inside as the temperatures begin to drop.

The Trouble With Temperature

Temperature is a funny thing. As gardeners, we are concerned with the temperature above and below the ground. Soil takes its time to warm up in the spring – it is affected by sun, rain and air temperature. Seeds will germinate with a soil temperature of 50°, but it takes longer. Ideal germination occurs between temperatures of 65°-80°. And, those are pretty good temperatures for growth. Because of the sheer mass of soil, temperatures don’t fluctuate much once they warm up.

round dial of a soil thermometer showing 70 degrees. — *Today, the soil temperature crossed the 70 degree mark*.

But air temperatures can have big swings from daytime highs to nighttime lows. This is where it gets tricky. The plants don’t like these swings any more than the madman does. Air temperature is just as funny as soil temperature, especially for the warm weather crops. Most of these plants can survive in temperatures of 50°, but growth isn’t the best. And, when the thermometer hits 95°, these plants just shut down. The best growth is somewhere in the middle, around 75° in the day and as low as 65° at night. But large swings in temperature can affect plants’ strength and fruit production.

two tomatoes with scaring near the blossom end — *Extreme temperature swings can cause ugly-looking tomatoes.* *Photo credit: UCCE Master Gardeners of Sacramento County*

Patience

The moral of this story is to have patience and keep an eye on the weather forecast. If you must plant, use a floating row cover to keep the cold off the plants and the warmth contained.

That’s too much work for the madman, so we are busy getting our beds ready – amending and preparing our soil. When the conditions are ripe, we’ll dig our holes; collar, fertilize and place our transplants and begin our succession planting of summer seeds. You can find our planting routine here.