Most growers hear the words ‘transplant shock’ and believe it’s nothing more than a newbie mistake that occurs when juvenile plants are mishandled during a move into larger pots or hydroponic systems. However, it turns out that many growers are putting their beloved babies through undue stress, time after time, crop after crop, without even realizing it! As a result, yields are decreased significantly even before the first flowers have formed. And, of course, we don’t want our plants to limp to the finishing line – we want them to sprint all the way!

We asked Kevin Anderson, a veteran indoor gardener in B.C., Canada, to give us his tips on how to handle transplants the right way.

So, What Exactly Are We Talking About?

Alrighty then. All you gorgeous growers out there will no doubt be familiar with the task of starting lots of seedlings or cuttings in propagators, perhaps in rockwool cubes or small seedling trays filled with growth media. Some of you may use those fancy cloning machines too – all well and good. But, sooner or later, it’s time to move your young, developing plants on to the next stage: a larger pot or a hydro system (e.g. ebb and flood table). This is called ‘transplanting.’

Crowded, leggy tomato plants, begging to be transplanted!

Transplanting is often considered the second most stressful event of a plant’s life, cloning being the first; however, there are many things we can do to minimize or even eliminate this stress.

True – much of the stress caused when transplanting is through delicate roots getting damaged as the plant is removed from its original pot and relocated. However, young plants more commonly suffer because they are placed under high intensity lighting too early. It’s not so much about how delicate your fingers are … it’s more about sudden changes in growing environment.

Before you remove the plant from its existing pot, prepare the new medium and be sure the environment is forgiving (more on this later). If transplanting to an inert medium (one that is devoid of nutrients, e.g. soilless mixes, coco coir, rockwool, and expanded clay pellets) it’s important to pre-load the medium with some nutrition. For cuttings this should be a fairly weak nutrient solution with an EC of 0.8 to 1.2 and for more mature plants 1.5 to 2 depending on species and size of plant.

For peat moss based soilless mediums, simply water until it is saturated with your own fertilizer mix. A good tip is to try adding some seaweed extract, which contains natural plant growth regulators / hormones that help stimulate root growth and reduce transplant shock. Always make sure your water / nutrient solution temperature is 68°F (20°C) to avoid shocking the roots with cold water or depriving them of oxygen with water that is too warm.

For rockwool simply soak the cube or slab as normal with the correct strength solution at a pH of 5.5 – 6.0 and a temperature of 68°F (20°C) for 24 hours, and then drain off the excess nutrient solution.

It All Comes Down To … Timing

For optimal results it’s important to transplant at just the right time. For clones this is when they have been fully hardened off and preferably have plenty of air-pruned roots showing from the cube or pellet. For more mature plants this is when the roots have fully filled the pot or cube but haven’t become root bound. To check if a plant is ready, gently squeeze the edges of the pot so the plant will come out with little effort. If you can see an abundance of roots just starting to creep along the edge of the pot, but they haven’t yet begun to fully circle, you are ready to transplant. If the soil or loose growing media starts to fall apart and there aren’t many visible roots, the plant is telling you that it needs a little longer in its current home before being transplanted.

One step at a time! Make sure not to transplant from a small pot to a very large pot as the medium will stay wet for too long, discouraging the roots from searching out water – this can lead to drowning and dampening off in severe cases. Potting up in stages also helps to produce a dense root mass. As a rough guide for many fast-growing vegetables, freshly rooted cuttings and seedlings will thrive if they are transplanted from a 2” to a 1 gallon sized pot and later into a 2-5 gallon pot. Be careful not to overwater new transplants as this will retard root development.

Here’s an important tip for growers who start off their cuttings / seedlings in rockwool and then move on to a soilless mix: be careful! Why? Because the soilless mix will wick water away from the rockwool and dry the cube out before the roots have ventured into the new soilless medium. You may find that you have to water the newly transplanted clones well before the soilless mix has dried because the cube itself is bone dry and houses most of the clone’s roots.

With a hydroponic medium like rockwool the same basic principles apply. A plant should be placed on a slab or into a larger cube when many roots are beginning to poke out the bottom of the existing cube. You can pull the plastic wrapper aside and check to see if there are plenty of roots showing. Again, you don’t want them to be circling the cube.

You really need to take care when removing the young plant from its original pot or seedling tray. Take your time. Gently squeeze around the root zone to loosen the plant from the pot. If transplanting from a seedling tray, try a gentle pinch at the bottom of the root zone – this pushes the seedling out of the tray easily.

If using loose growth media, place it lovingly into a pre-dug hole and gently backfill the hole and consolidate the media around the plant. Be careful not to compact the media (especially if using soil) when you back-fill the hole, but make sure you haven’t left any large air pockets. Then lightly water again to really settle the media around the newly-transplanted specimen.

Environment for Transplants

Okay, so we’ve been gentle and moved our seedlings or cuttings into their new homes. What about the growing environment? How can you tweak this to allow the plant the easiest transition possible? Remember, the aim of the game here is to give the roots an easy time so they can focus their energy on growing and extending their network, rather than all their energy being monopolized with supplying water and nutrients to a struggling plant.

Newly transplanted cuttings or seedlings hate hot and dry conditions. Too much air movement will increase stress too, by forcing the plant to transpire more than necessary. An unforgiving environment will force the young root system to work hard, just to keep up with the transpiration through the leaves. The trick is to keep humidity levels high (70-80%) and gradually wean them to levels around 60%. Humidity plays a HUGE part in determining how hard the roots have to work, so keeping the humidity at around 70-80% for the first few days using humidity domes or Victorian Bell Cloches is a great way to maintain higher humidity levels around single plants.

Domes and cloches can be removed for increasing periods of time to allow your plants to gradually acclimatize to their new vegetative environment.

Temperature should be kept at no more than 75°F (24°C) and no cooler than 70°F (21°C): the warm temperature will help ease the plant through the transition.

Blinded by the Lights

During this delicate transition, don’t go overboard with the lights! It’s so easy to get carried away and get over zealous in the early stages. Remember, the more light you give your plants the more the roots will need to spend their energy supplying the plant with water and food for it to utilize this light. Not a bad thing when you have a large established root system, but just after transplanting it is much better to allow the plant time to establish its roots rather than putting them to work at full tilt.

It’s common for indoor gardeners to move their plants from a fluorescent T5 fixture to a metal halide. Suddenly your plants are receiving far more light and enjoying lots more space than they had in the propagator or seedling tray. It doesn’t matter how delicately you handled the transplantation: young plants simply cannot keep up with the huge demand a high intensity grow light puts on them, especially in a demanding environment. The droop you will inevitably see is simply a symptom of the roots being unable to supply the plant with enough water in order to keep up with its demands. As with everything you do in the indoor garden, it is important to make changes slowly and gently, easing plants into more demanding environments as softly/gently as possible. Clones in particular should be broken into the more intense lighting conditions as gently and gradually as possible.

To minimize shock, always raise HID grow lights at least 4-5 feet above the plant for 1000 Watt bulbs and 3-4 feet for 600 watt bulbs. I know, I know – the lights look way too high, but I assure you this is enough light for the young plants to photosynthesize and, crucially, it doesn’t put too much strain on the root system. Dimmable ballasts work great here as you can save energy by simply dialing back on the intensity. After a few days and once you see the emergence of new growth you are safe to start increasing the ballasts back to full strength and / or lowering the lights.

Got a transplanting tip you want to share? Do you have a particular product or technique that you swear by? Share your wisdom by posting a comment below!