How can I trick plants into thinking there's more space in the pot so they grow larger?

Question

I think I read somewhere about rearranging plant's roots in certain ways within the soil inside a pot to make it think it's growing in a larger space, and as a result let it grow bigger, as if it was planted in a large pot. I don't remember any details, and what I've tried so far hasn't shown significant results, so I'd like to know if it's even possible to achieve this effect − make the plant grow larger without increasing the soil volume.

I think one of the ways was to make horizontal layers where water would accumulate like on the bottom of the pot, effectively increasing the number of "bottoms" inside a pot, but I couldn't create such a structure at home.

Ultimately what I want to achieve is to grow larger plants on a small balcony (or window sill) with limited space for pots.

Currently I have two citrus plants growing at their limit of 1.5m (5ft), due to available soil in their pots, 20cm (8in) deep, 20cm (8in) wide, and I'm also planning on planting golden raspberry and almond from seeds. My available sill space is 80cm (31in) by 20cm (8in), and ~2m (~6.5ft) in height, and the balcony space is roughly 20cm (8in) by 4m (13ft), but the cold days have started and I've moved the only 2 pots I care about to the sill. I'd like to at least grow the almond seeds now and repot them closer to spring into bigger pots, and then maybe move them to the country house's grounds next year. We'll see how that goes.

Answer 1

You can't - roots need to grow, and as they grow, the plant grows. If the roots run out of room, then the plant doesn't get bigger. Try using tall, narrow pots, something like long tom pots, on the balcony - more room for roots with a much smaller footprint.

Answer 2

take this with a grain of salt but how about trying some air pruning by using a grow pot. Its those pots that are made of some sort of canvas and it allows the soil better aeration. I read that roots in regular pots will normally just get root bound over time and they don't really make good use of the rest of the soil but when you put them in grow pots/ grow bags this allows the roots to prune themselves once they hit the edges and thus they won't go around in circles but instead they will focus of growing those side roots which then will make better and efficient use of the rest of the soil. I've just started planting pepper plants myself and once they are big enough I'll transplant them into grow bags for better growth.

Answer 3

I'm not sure about ways involving some roots, but I have an idea (and a method besides that is decently helpful).

First the helpful method:

Foliar sprays of fertilizer. Leaves can essentially act like roots when it comes to absorbing nutrients. So, you can take advantage of that. Miracle Gro has most of the nutrients you'll need, but the bulk of soil probably has a few things that Miracle Gro doesn't (like calcium, which is important for growth, and magnesium). You could dissolve some limestone, dolomite lime, or eggshells in vinegar to create some water soluble calcium (let the vinegar turn to water before you use it, though). Fertilizing the soil could be important, too. Fertilizing well will help a plant grow significantly larger than if you don't fertilize well.

Second, my hypothesis:

I've read that plant roots pretty much only grow around the sides and bottom of the pots they're in. They basically leave the middle of the soil untouched. I observed things since, and that seems pretty close to true. So, getting your plant to somehow get roots in the middle of the pot might help (although I imagine your soil would get depleted of nutrients faster).

Here's what you could do:

Get a pot. Get some flat sections that roots can't grow through. Put them between layers of soil in the pot. Transplant into the top layer. Wait until the plant gets rootbound on the top layer. Then take that layer out and remove the first divider. Then put the plant and it's top layer of soil back in, so the roots can grow into the second layer. Let it get rootbound again. Then repeat until roots are althroughout the soil. However, if the roots happen to be able to move, somehow, rather than just grow, they might frustrate this plan.

I don't know if this will help the plant get any bigger, though. There might be reasons plants prefer not to grow in the middle.