A few weeks after sowing your fruit and vegetable seeds indoors, they have sprouted and grown. Now they have 4 to 6 leaves, and you’ve been told that you absolutely must transplant these seedlings. It’s an essential step in indoor seedling production, we’re sometimes warned!
Yet I rarely transplant my seedlings. How is this possible? I’ll explain, but first a few details.
Transplanting
The word “transplant” is used in many different ways, but basically it means to take a plant and put it in another container or location. It can also be replaced by the terms “transplanting” or “replanting”.
Often, however, “transplanting” is used to refer to the transplanting of young seedlings that have been sown loose in a germination tray and then transferred to individual pots, or to refer to the repotting of a seedling into a larger pot.
Why Transplant?
Of course, as your seedlings grow, they need more room to develop their roots. A larger container holds more potting soil and therefore more water and nutrients, which growing seedlings need. It’s also a question of sharing resources. By transferring seedlings to larger containers, they are spaced out and receive more light and better aeration, which will reduce the incidence of fungal diseases.
But why can’t we plant our seeds directly in larger pots? This technique is blamed for all kinds of problems, while at the same time lending virtues to transplanting. Among other things, we sometimes hear that the shock of transplanting strengthens the seedlings’ root system and stimulates growth. It’s also said that a pot that’s too big for a plant won’t dry out fast enough, leading to root rot.
The Truth
Transplanting damages the roots of your seedlings and this stress delays their growth. If you notice that root development increases after transplanting, this is not stimulation. Either the plant has lost roots in the process and needs to produce more, or it didn’t have enough room in its original pot and can now afford to expand.
The roots of seedlings in large pots have better access to resources and are less hindered by the container wall. Since leaf and root growth are interdependent, a small pot limits this growth. In some cases, such as with tomatoes, larger containers may increase the yield of certain crops.
It’s a myth that potting soil remains too moist and causes plant roots to rot. Potted plants can be completely soaked in water without damage, as long as the pot is left to drain afterwards. What’s harmful to plants is excessive daily watering.
A small plant in a large pot needs to be watered less often. Commercial potting soils, which are extremely porous, don’t present this problem. In fact, you’re more likely to lose seedlings through lack of water than through excess, as small containers can dry out very quickly under certain conditions.
So Why Transplant Indoors?
There are, however, several advantages to starting with small containers and increasing their size as the plant grows, but this is more interesting when producing seedlings in large quantities.
To begin with, by sowing several seeds in a germination tray, you can choose the healthiest seedlings. You also avoid ending up with empty pots.
It also saves space and resources. Starting seedlings in multi-cell trays considerably reduces the space required, compared with seedlings in 10 cm (4 inch) pots. In the case of greenhouse production, by reducing space, you can also reduce heating and artificial lighting, and therefore use less electricity or gas.
It also means less fertilizer can be used. All this leads to significant cost reductions, and has been well studied by the horticultural industry.
The Laidback Gardener’s Method
Do you have to transplant seedlings indoors? My vegetable garden consists of about twenty containers, of all kinds, on a downtown terrace. So it’s not a huge production! I use the same light for seedlings, whether for one plant or 40. So I don’t need to optimize my space and use of resources.
For this reason, I plant almost all my seeds directly in pots. I use small 5 cm pots for small plants that are grown indoors for a short period (less than 4 weeks), such as lettuces. For plants that are kept indoors for longer periods, such as tomatoes and peppers, I use 10 cm pots, where they will remain until I transplant them outdoors. This is the technique my father taught me.
To prevent empty pots, I plant 2 or 3 seeds per pot and if several germinate, I choose the most beautiful seedling. Of course, I need more seeds, but with the quantity in each bag, I wouldn’t be able to use them all anyway!
If your seedlings are getting too big for their original pots and there’s still time before transplanting to the garden, it’s still a good idea to transplant them into larger pots. Keeping a young plant in a pot that’s too narrow can be detrimental to its development once transplanted outdoors.
That’s why I rarely start seedlings more than 6 weeks before transplanting them outdoors. This saves me from having to transplant them. Those who sow earlier indoors and transplant will have their crops sooner, I know. But studies have shown that it doesn’t increase the yield.
A Hybrid Solution?
I wouldn’t say that one method is better than the other; they’re just more or less suited to certain situations. You could also opt for a hybrid solution by transplanting young seedlings produced in a germination tray directly into 10 cm pots. The best of both worlds? I don’t know, having never tried it. Do any of you use this method?
