Why You Need To Know The Soil Temp In Your Garden

These four are paramount to success in any vegetable garden, no matter where you grow. 

1. You need good seed and/or rootstock.
2. Your garden needs the right aspect. 
3. You need to distribute water. 
4. Your soil must be nutrient rich and alive.

The Forgotten Pillar

These four pillars are commonly accepted and understood. If you live at sea level, that’s probably all you need to know. Up here in our Unpredictable Highland Climate there is a fifth pillar that will need to be understood and monitored if you wish to have repeatable success with your Spring/Summer plantings. 

The conditions are mild at sea level, compared to our altitude of 700m. In winter, our hard frosts and winds create unique challenges for our soil, stripping it of moisture and reducing microbe and fungi habitat. If it gets too dry the soil food web will be terminated and plant growth will be stifled.

Timing

Our icy winters reduce the temperature in the soil, limiting what vegetables can be grown and when to stop planting. We have been collecting our seed for many years to reduce the strike temp of our collection by several degrees. Saving the seed for highland growing allows us to succession plant later into winter and provides more opportunities for success. 

Growing vegetables in the cold is easier than you think, especially if we grow as Grandmas Grandma did. The hard part about growing in our Unpredictable Highland Climate is getting the timing right for Spring/Summer plantings and that’s why we collect data.

I bang on about soil temp a lot, and for good reason. It is the only way to know when Spring has sprung in your garden each year. More importantly, it is the only way to know when to plant each Summer vegetable. Planting with soil temp gets you eating your own produce throughout Summer, rather than all at the end. 

Each vegetable has a preferred root temp. Match each seedling with optimum soil temp and your little seedling will continue to grow as soon as it is put in the ground. Put your seedling in the ground at a lower than preferred temp, and your seedling will sit still and wait for the roots to be warm enough to start growing. 

How/When To Test?

Monitoring your soil temp is paramount to Spring success in any highland garden. As mentioned in previous articles, I test daily at 10am. After the frost/fog has melted and before the sun has much effect.

I test all my garden beds to note the differences in microclimates. They all have a similar aspect but are planted with different trees to provide varying protection and nutrient. At this time of year, the shade is increased as the leaves fill out the canopy and the arc of the sun gets higher in the sky. 

Soil Temps

One of my beds is under gum trees and the sun now shines over the canopy creating shade on the garden. It still sits at 15C, after climbing rapidly in early spring. These 3 tomatoes were planted weeks ago and 2 have been replanted from frost and wind loss. 

Nearby downhill where there are no shading gums, the soil temp is 17C. Its only 2 degrees, but the Tomatoes look very different. The lower bed is ready for Cucumbers and almost ready for Capsicum and Chillies at 18C. 

I still have beds to prepare for other Summer crops. They will take Pumpkins and Watermelons, but only when the new live soil delivers 20C. I will plant under trees in those exposed beds, using the leafy canopy to protect from random frosts, saving me from boxing.

The Demanding Nightshade

The vegetable that may surprise you is Eggplant. The rootzone needs to be 24C+, this might explain why you’ve had limited success, so you will need a special spot to grow it early. Or you could run a hydroponic or aquaculture system and install a heater. Flowing warm water over the roots will get your Eggplant growing sooner than the rest of us.

Air Temps

The ambient air temp is not nearly as important as you might think. In Spring the daytime air temps are favourable to most vegetable seedlings it is only the overnight temps that are unfavourable, but only some nights, so box it. 

This past week we’ve had a 14C overnight, my Tomatoes might’ve grew while I slept. If the root zone is hugged by soil that is optimum temp or above, growth will be witnessed. Quietly, under the ground there is a lot of action happening. The rootzone is growing and building a relationship with the microbes in the soil, to provide a powerhouse for growth and fruit production.

Monitor your soil temp and get your grow on surprisingly sooner than you think. What are you waiting for?

Stay Awesome

The Gordon Gnohm