These days there is a curse in the living room every time someone bumps into one of my crates. The pre-sowing has again gotten out of hand, and in a long line to the front door there are fifteen wooden boxes full of young plants, which have to go outside for a few hours every day and then back in again. This is called hardening off: the plants are given two weeks to get used to cold, rain, wind and sun. Then, in the week after ice saints (May 11-15), they go outside for good. That’s how I did it for years, because that’s what it says in all my books. Then I read that gardenfluencer Charles Dowding calls all that dragging back and forth “a persistent myth” and “a waste of time”. Ouch.
An extra blanket
“I know it is said in gardening books: put the plants outside for a few hours during the day, and then bring them back in in the evening,” says Heleen Calcoen from Kweek nursery. “I personally think that is a waste of energy, it is not necessary, and a lot of effort for little effect. I don’t have the time for it either, so I looked for a way around it.” The road around it looks something like this: all plants go outside as quickly as possible. Only the aubergines and peppers, which need extra heat, stay indoors until ice cold, but then go outside without much fuss. What she does provide for the first cold, or for sensitive plants, is an extra blanket: it microclimate cloth*.
“You put a microclimate cloth like this over your plants, it keeps out the cold and the worst wind, while still allowing sunlight to pass through. What I also often do is lay down a thick layer of mulch made of straw or hay. But you can even use an old cotton sheet to quickly throw over your plants if the temperature suddenly drops. Mulch has the advantage of keeping weeds at bay somewhat. The only thing you need to know: the soil heats up less quickly under that mulch layer, so it is good to move it aside on hot days.”
Furthermore, Heleen believes in a kind of “reverse version of hardening off”: you can put the plants outside on nice days, because they then benefit from the sunlight. “If you have grown a tomato plant in the living room and you place it outside on a sunny day, the wind can blow through it a bit, so that it takes maximum root, and it also gets full light, which is not always evident indoors. That benefits growth.”
Everything that germinates goes outside
“Oh, but hardening off is super important,” says Michiel Demey from De Verwildering nursery when we ask him about it. But he also has something different in mind than what the garden books prescribe. In his nursery, the plants are placed outside as soon as they have germinated, so that they continue to grow slowly and strongly. No dragging boxes back and forth, it’s hardening from the start.
© Kaat Schaubroeck
“Let them get used to it hour by hour? That’s really pampering, isn’t it? That’s not necessary. But for every plant the relationship with light and heat is important. The warmer it is, the more light it needs. It is very warm on the average windowsill and only gets light from one side. So it will grow long and lanky and the basic rule is: a plant that starts to stretch weakens. You also often see this happen with sunflowers on the windowsill, or with zucchini and pumpkins. And if they are weaker, they are also much more likely to be attacked by snails. We strive for compact, sturdy plants. We put pre-sown cabbages outside immediately after germination. Even the tomatoes have been there all month now (April, ed.) outside.”
The entire month of April? (Your reporter needs some time to recover.) So even if the temperatures drop so low, they are allowed outside? Aren’t they often indoors in the garden centre? “We sow them indoors in February-March, then they go into the unheated greenhouse, and as soon as they get their first real leaves, we prick them out and then they fly outside. Only when it freezes will we of course bring them back in. They now have a nice thick trunk and a sturdy root system, which can withstand a blow. When I see tomato plants still indoors in the garden center, I honestly find it a bit bizarre, because it is warm there and they don’t get enough light. If you get your plants there, be sure to look for specimens that are not too large, but rather stocky and sturdy.”
Don’t stress, see what works
It is a misunderstanding for both Heleen and Michiel that plants are immediately destroyed if they suffer a bit or have to “work” to survive. Heleen: “I have experienced sudden frost at the end of May, all the peppers and aubergines had already been planted, and the leaves were indeed frozen, but the plants were not lost. That is of course not what you want, and you will experience a lot of delays in the season, but plants are stronger than we think. It’s a bit like with people: what doesn’t kill you, makes you stronger. Sometimes I will even deliberately damage the roots of tomato plants a little when transplanting; This gives the plant a push to produce extra roots.”
It should be warm enough now anyway, says Michiel: “If you still have plants indoors, be sure to put them outside. If they are very fragile, you can possibly place a climate cloth over them. My ultimate tip is: observe and evaluate. Look at your plants. If they look nice, you can keep aubergines and peppers indoors for a while if necessary. But if you notice that they are also starting to stretch: put them outside, where they will get a lot more light now anyway.”
“I’m always a bit afraid of the do’s and don’ts,” Heleen concludes. “People who order seeds often get the feeling that they are immediately buying the failure. They read everything, try to rule out all risks, and actually the stress takes the fun out of vegetable gardening. My idea is: you learn by doing what works best for you. Learn to follow your feelings: it can remain relaxing, right?
This weekend you can go to the organic plant sales of Kwekerij Kweek on the Beervelde garden days. De Verwildering is open every Saturday from 9 a.m. to 5 p.m. until the end of June. deverwildering.be andkwekerijweek.be
*A microclimate cloth (howitec netting) you buy per running meter. The fabric creates a temperate microclimate by breaking light frost, heavy rain, hail and wind, yet allowing plenty of sun to pass through. The canvas stretches and is therefore easy to stretch. In addition, it protects against birds, rodents and larger insects such as the cabbage butterfly.
In brief
-The more heat plants receive, the more light they need. If the relationship is lost, they will stretch. In that case, be sure to put them outside.
-Go for slow plants that grow in a cold room or (better yet) outside. This makes them firm and compact, and less vulnerable to snails.
-Keep an eye on the weather forecast – frost is especially fatal for tomatoes, peppers and aubergines – but plants are not puppies: you don’t have to pamper them, they can handle something and will recover.
-If necessary, invest in a microclimate cloth, for the most delicate plants or sudden night frost. You can also bridge the coldest nights with a thick pack of hay or straw, or with an old sheet.
