I’m a big advocate of starting many of my vegetables in modules or containers and moving them into my garden as they mature. For a small garden, this method ensures that I don’t get as many empty patches as I would get with direct sowing and spotty germination. But starting seeds indoors has its trade-offs, and the biggest one is transplant shock.
Transplant shock means the plant has activated its survival mechanisms after being moved outside into the elements. It manifests through wilting, yellowing, curling of the leaves, and even dying off. The roots do whatever it takes to survive and dictate to the plant to shut down and conserve energy.
For seedlings grown indoors, unaccustomed to the full strength of the sun, you may notice scalding. The picture above shows a swede seedling that has been sunburnt because of insufficient hardening off. Leaves become pale, almost white and fall off. Fortunately, the plants recovered, but that doesn’t always happen with sunburn.
Most seedlings will wilt after transplanting, and that’s entirely normal. If you see your small plants wilting or yellowing, it doesn’t necessarily mean you’ve done something wrong. What’s important is that they pull through. Most plants will recover from transplant shock, and the main sign of recovery is new growth. Check for young leaves developing in the middle of the plant – that’s always good news.
There’s no coming back for the leaves that are severely damaged – it’s best to prune them once you see new growth so that the plant can focus its resources where it makes a difference.
How to handle transplant shock in seedlings
Transplant shock may be unavoidable, but it doesn’t have to get very dramatic. There are plenty of things you could do to prevent transplant shock from killing off your seedlings entirely. Pay attention to how you handle your plants from their life indoors or in the greenhouse to their new home outside.
1. Don’t skip hardening off
Seedlings grown indoors under grow lights, where the temperature is nice and cozy, will have a major shock when moved outside without any adaptation period. There’s no wind indoors, no temperature variations, and the grow lights are no substitute for the sun, although having strong lights with a full spectrum helps a great deal. This is why getting your indoor seedlings gradually accustomed to the great outdoors is so important for their survival.
If you’re growing your seedlings in a greenhouse, polytunnel, or cold frame, they probably stand a better chance, as they have direct access to sunlight, and the weather can get pretty chilly inside those structures as well. Seedlings grown under cover outside may not need too much adapting, but hardening them off could be a good idea nonetheless.
Hardening off is the process of getting your seedling ready for transplanting by gradually increasing the time they spend outside. Start with one hour in a shady spot, and increase by one to two hours each day over the course of a week. While hardening seedlings off, water them less often. This will provide “good” stress to your plants, enough to make them sturdy and resilient by the time they need to be transplanted.
While moving seedling trays from one place to another may seem like a tedious task, it’s well worth it if it means keeping most of your seedlings alive. A shelving unit on wheels could be a great solution for carrying trays outside, rather than just moving them one by one.
However, if you’re not willing to go through all that hassle, there’s a shortcut to getting your plants used to the outdoors. Check this article to learn more about the lazy hardening off method.
2. Check the weather and offer protection
As gardeners, it’s sometimes hard to stay patient and stay in tune with the moody seasons. I’ve often made the mistake of moving seedlings outside when the nights were still too cold. As a result, the transplant shock was twofold – my plants had to survive being transplanted but also endure freezing temperatures at night.
Always check the weather before transplanting your seedlings outside. How cold will the nights get over the course of the following week? If you know you’ll be getting hard frosts, it’s perhaps best you wait. Even the most cold-hardy crops are still babies at this point. They don’t have the same stamina to withstand snow and frosts as mature plants do.
Another thing I like to do in early spring is to protect my newly transplanted seedlings with a layer of garden fabric. If the weather gets particularly cold, I even double down on fleece and add another layer. This ensures they won’t be as affected by frosts and strong winds. Here’s an example of row covers I like to use.
Heat can harm seedlings as well. Whatever you do, don’t transplant your seedlings on a hot day. Wait until the weather is overcast and transplant them in the afternoon or evening so that they have all night long to establish their roots and absorb all the necessary moisture.
And lastly, wait until it’s completely safe from frosts before planting your heat-loving crops outside, like peppers, aubergines, tomatoes, and the likes. Check for the last frost date for your area, check the weather, and add a week or two to that date for safety.
3. Water thoroughly before and after transplanting
While waterlogging your seedlings is usually a bad thing because it leads to damping off disease and drowning the roots, soaking your young plants just before transplanting is very important. This helps you handle the plants and get them out of their module trays hassle-free, but it also provides them with the moisture they need.
If at any point during the transplant, the plant’s roots become dry, it will cause major wilting and shock. Immediately after transplanting, give your seedlings a good drink of water and continue to water them throughout the first week.
Watering your seedlings is the single best thing you could do to ease the transplant shock. You can even water them through the row covers, as the water gently seeps through the fabric. Always check the ground for moisture levels at this point and use mulch or drip line irrigation to ensure constant humidity levels.
4. Don’t be afraid to prune the plant
While leaves are important, foliage is constantly changing and regenerating. When transplanting our seedlings, we should focus on pruning off some of the plants so that the roots have fewer leaves to worry about.
For large plants such as peppers, tomatoes, eggplants, zucchini, or cucumber, this may mean pruning off the lower leaves. Removing a quarter to a third of the leaves is a good rule of thumb. This doesn’t hurt the plant. In fact, it stimulates even more growth and helps the roots establish faster.
However, if your seedlings are small and barely a month old, like in the case of cool weather crops, pruning them isn’t always an option, as they don’t have a lot of leaves, to begin with. While suffering from transplant shock, some of these small seedlings will show signs of yellowing leaves, and you can trim those if you like. But in most cases, the plants will drop those wilted leaves on their own.
5. Don’t disturb the roots during transplant
When transplanting your seedlings, resist the urge of teasing their roots, shaking the growing medium off, or even trimming or breaking up the root ball. If you have a seedling that’s rootbound, it’s okay to slightly untangle some of the roots so that they can access the soil more easily – but I don’t always do that, and I can’t tell the difference when I do.
Some plants, like peas, beans, and cucumbers, are known to handle transplanting poorly, so disturbing their roots is not a good idea. Many gardeners take extra measures when starting these plants from seeds. You can start peas inside long rain gutters and slide them to their new location.
Beans grow very well in toilet paper rolls, which fixes the problem of having to take them out of their containers. Plant them in the ground as they are, and the cardboard rolls will easily break down.
Cucumber, zucchini, and squash don’t fit inside toilet paper rolls, and peat containers don’t dissolve as well as advertised, so what you can do is create your own containers out of newspaper. Stack multiple layers together and create biodegradable paper cups for these sensitive plants. This will considerably ease transplant shock for plants prone to root disturbance problems.
6. Plant size considerations
You’ve probably read that the larger the plant, the better it will withstand pests and diseases, and that’s partly true. A more mature seedling will be better equipped to defend itself, especially during flea beetle and aphid season.
However, when it comes to transplanting plants outside, you’ll often see young seedlings do better than older plants. This is especially true for cold-hardy crops. Small, healthy seedlings will quickly catch up and overtake earlier sowings that have grown too large and have started to struggle.
Small plants often do better when moved outside because their root system is so small that they barely notice the change. It takes them less time to get established and shoot up new growth. By comparison, an older seedling might already be stressed from lacking nutrients and space for its roots inside the modules, making it less resistant in the long run.
With tomatoes, peppers, chilies, and aubergines, we have no choice but to transplant these when they’re already 8 to 12 weeks old. If you’re buying your starts from a local nursery, get sturdy and healthy plants and choose the ones displayed outside rather than the ones indoors. These days, many online nurseries offer safe delivery and that can be an option as well. You will still have to fertilize them and harden them off because they may not have been hardened off properly.
How long until plants recover from transplant shock?
Hopefully, you’re feeling less worried about transplant shock and seeing it as a necessary evil to get early crops and densely planted raised beds. It’s important to remember that transplant shock is just a phase, and it will soon pass. If you’re getting antsy, know that it takes the roots about a week to get established and up to two weeks for new leaves to shoot up.
If your plants are still looking wilted and lifeless after two weeks, you should start looking for alternatives: direct sowing, starting a new batch of seedlings, or buying new starts from the nursery.
Should you fertilize after transplanting?
If your soil is well amended with compost, your newly transplanted seedlings might not need fertilizing during the first weeks outside, but it all depends on the plant. Some plants are heavy feeders, and others do well within the soil that’s available to them.
If you choose to fertilize right away, you should be aware that a fertilizer that’s too strong could do more harm than good. Choose a mild fertilizer in liquid form so that the seedlings can easily access it and dilute it to half-strength. For this purpose, the best organic fertilizers are fish emulsion, earthworm tea, and seaweed extract.
Don’t let the sad look of your newly transplanted seedlings put you off. I know it can be hard to watch all that hard work seem to go to waste, and you wish that there’s more that you could do, but this is how plants usually toughen up. This is not to say that you shouldn’t have spare plants available in case anything goes wrong.
Besides transplant shock, you could still lose a handful of your seedlings to slugs, birds, or rabbits. That’s how gardening is, and we have to share some of our work with the wildlife inhabitants of our garden. We win some, and we lose some – hopefully, by summer, we’ll have enough harvest to make all this hard work worth it!