Although I have already written about how to plant onions in fall and leave them during winter, there is one more approach which can be considered. If you already have grown onions, then I’m free to say that you have pretty good base knowledge which will be required. However, the devil is in the detail, as they say. Therefore, here’s my guide.
As you will see, learning how to grow onions in containers is not rocket science, but still, there are specific areas which must be covered, so that you can expect a good harvest.
Why Bother With Growing In Containers When I Can Leave Them Out For The Winter?
To be honest, the most straightforward approach would be to leave a couple of lines of the autumn harvest for overwintering. Just apply straw for cover, and that is it. But if you do so, where is the fun in this approach?
Of course, there are two main reasons to use this approach to grow onions when the terms are not good (read knee-deep snow). The first one is that during overwintering there are fewer chances that you can cut off green leaves and consume them. So, if you want to have spring onions in January, with overwintering, it is impossible.
The second one is that in some regions winters are so bitterly cold that not the onions which are famous for being hardy plants will not survive. Luckily, an approach which includes containers and onions is not conditioned to be used just in these areas. The main advantage of this system is that it can be used anywhere and anytime.
What Will Be Needed For Successful Growing?
If you have pots of flowers in your house, then you know that this is the most common way of container growing. Unfortunately, onions will require a bit of space, so bigger pots or even better, crates, are the first and most important thing. If you don’t have a box at hand, you can hop online and buy one of those army-grade ones. They are sturdy, durable, and convenient for relocating and can sustain weight pretty good. The other option is to make one by yourself.
As for the soil for onions, there are also two approaches. One is to buy pre-made soil for pot plants, with pH from 6.0 to 6.8. To be sure, grab yourself one of those pH testers, just to see if the soil you have bought has the perfect level of acidity. The other one is to take a large bucket or a bathtub, add several buckets of dirt, infuse manure and turn over once in every few days for several weeks. This will enrich the soil and can be made earlier, to save you the trouble.
Of course, you will need onions as well. As for sowing, you can sow the seeds or pods. Personally, I’m a fan of the second approach, since it makes things a lot easier; there is no need to worry and take care of young plants. Plus, it shortens the maturing time. As for variety, you can go with any spring onions, since they require less space, or choose smaller bulbing variety such as Crystal Wax.
The other things which may be needed are fertilizer, a spade, a shovel and space of course. You will need two fertilizer types, perhaps. In the beginning, while the bulbing phase is in full swing, that which is richer in Nitrogen will be required (21:0:0). Later, when the bulb develops, use that with a higher level of phosphorus. It will feed the leaves, making them taste better.
How To Prepare?
When it comes to timeframe, as I said, there is no general rule on this matter. Onions will be safe from frost and will grow uninterrupted. The trouble is that onions will require a lot of sunlight. If we take into consideration that they will need at least six hours of sun, it is clear that darker months such as December and January are not the best for growing onions. On the other hand, if you plan to use UV light, feel free to start whenever it suits you.
Also, in this period, you can disinfect the soil you either bought or made. To do so, take a baking trellis, put a thin layer of soil inside and bake it at low temperature for about 15 minutes. This is done to remove and kill any eggs or mushroom spores which can appear later and can disturb onions pretty much.
How To Sow?
Depending on the variety you choose, the container should be appropriately sized. If you plan on growing spring onions, you can go with a rectangular larger flower pot. You can plant spring onions in a single row there since they don’t require a lot of space. On the other hand, bulbing varieties will need at least 4” space between, so that army crate I mentioned before will be the best course of action. Mind that in both cases the depth of the container should be at least 10”, and to have enough drainage holes.
The process of sowing is the same as with the garden. Dig a line or row about 3” deep, and put one pod on every 4”. If you are sowing seeds, spread them evenly. Cover the seeds or pod with soil and water until the ground is soaked. This will give a fantastic head start for young plants. Often watering will be needed for the next month or several weeks. Usually, the soil around onions is pressed to eject air from the ground so that you can do this as well.
Also, if you wish to have a continuous supply of green leaves, you can separate the pods into several groups and plant them in one week apart. This way the harvest will be uninterrupted so that you can enjoy leaves longer.
Besides watering, fertilizer is essential in these first few days. If the soil is not rich in nutrients, apply matching fertilizer. For pods, the best course of action is to use Phosphorus-rich fertilizer. If you are uncertain on which to try, I’ve written about some recipes for liquid organic fertilizers, so feel free to use this list.
How To Do Maintenance?
Maintaining onions is not a difficult task, luckily. They will require regular watering, which can be more often than with onions grown in gardens, because indoors the temperature is higher, and the ground dries faster. Also, there is an important question of sunlight.
I have mentioned that onions will need at least six hours of sun (although eight is far better). Because of that, the container should be placed somewhere near the window where the sun will provide precious light. If you have opted for bulbing varieties and smaller containers, you should move them around one at a time without much issue.
But, in case that you went with a crate for the container, moving one around can be challenging. The crate is heavy already, but once filled with dirt, it can be nearly impossible to move. Therefore, ask for help from friends or relatives. Of course, elder people shouldn’t try to move it, because of possible back injuries.
Other than watering approximately once a week, there is not much to do. Weeds are not likely to develop but keep close look nonetheless. As for the pests, the only way they can reach your plants is via soil, but if you sterilized the ground, the chances are minimal. Nonetheless, every weed should be removed immediately, and pests can be dealt with quickly by using pyrethrin, or other kinds of organic pest control methods.
On the other hand, different kinds of rots and viruses can strike onions regardless of the season. It is true that infections are somewhat less sure to happen in cold weather, but many of them are airborne (imagine viruses in military uniforms with patches of 101st Airborne on their sleeves; hilarious), and can activate when attached on plants.
In order to boost the growth a bit, I can recommend you to use Microbial Inoculants which will help your plants to grow better and stronger. Of course, these will not replace fertilizers, but will improve the process of photosynthesis. Since there is lack of space, you can boost the results, instead of increasing the intake of nutrients.
How To Harvest?
The main advantage of container-based growing is the versatility. Imagine that you are making dinner and that you wish to have fresh onion leaves as a salad. Take the scissors, and cut the green leaves about 1” above the ground. That is it; harvesting is done. As long as the plants are watered and supplied with fertilizer, they will continue to grow and produce new leaves.
As for versatility; if you decide that you want to leave them to mature fully, just stop cutting leaves. They will grow until leaves start turning brown, and will wither in the end. Just pull out bulbs and remove any dirt from it and you are good to go!
So, there it is. My guide on how to grow onions in containers is at your disposal. As I’ve said, it is not such a big deal. Onions are very convenient for growing in general, and putting them in containers makes all the care almost trivial. If you haven’t tried it before, you should!
Microbial Inoculants are great addition to your garden, so be sure to check them out!
As always, if you have any comments, opinion or advice, feel free to leave it in the comment section below.