This is not a "new approach" and is done as a remedy to mitigate a particular problem, not as a standard propagation technique. I just used up all my big words.

It is called "Trenching" and not really sideway.
It is done with extra lanky plants. Even then you can plant them normally, a bit deeper , supported with small temporary stick/stake.

Seysonn

If the plant is too tall, planting it upright puts the roots in cooler ground. This slows the plant development. In zone 3A the ground can be a lot cooler 12 inches deep.

Agree. It has long been a common practice and works well. Of course it is better to not have the overly tall lanky plants to begin with.

Dave

So what I can understand from comments it is done only for tall lanky plants. It is new approach for me, I am not saying that it is a new thing generally.

Thanks, everyone!

I did it last year with two Sungolds I had inside for a month. ( The weather never co-operated to plant them sooner). They had more tomatoes on them than any other cherry tomato I ever had.

I have done this every time my seedlings got too tall before I could plant them. They did fine, as the whole buried stems grew roots. Just remember or mark which way your sideways plant is buried so you won't cultivate the buried portion.

Hi Alex, its not only for lanky plants, its a good idea for those in colder climates so that the root system is nearer to the surface where the soil is warmer.

In hotter climates, its prob better to plant them in the traditional way so the roots are deeper and cooler.

I don't know about the ground temperature issue. Actually heat comes up from the ground too. And it is warmer deeper in the ground than on/near the surface early in the season. Besides that, when planted vertically, deeper, the buried portion of the stem will grow root as well

see the picture

Seysonn

I'll try to play around with deep planting and trenching next summer - see how it goes...