5 Plant-Killing Mistakes to Avoid When Growing Seedlings and Transplanting Them in Your Garden

Yeah! The planting season is in full swing and you have lots of seedlings to transplant into your garden? Great news, but… You may end up with just a few, sometimes weak, and disappointing vegetables if you are not careful. Inexperienced and amateur gardeners may end up with empty plates, unless they correct some very common mistakes when transplanting your tomatoes, leeks or peppers… And these can be deadly – not for you though, for them…

Let’s go through the 5 most common and dangerous mistakes most amateur gardeners make when transplanting seedlings in their garden, so, unlike them, you will have a bountiful season of healthy and generous crops. Off we go!

Mistake Nr 1 – Leggy Seedlings

Planting a leggy seedling, with long and slender stems, can be a death sentence for your little green friend, and in any case, it does not give it the best start in life in your garden! If it manages to recover, you will still have a weak and underproductive adult plant, so, the question is…

Leggy Seedlings

What is a leggy seedling?

A leggy seedling is a small plant that’s too tall and spindly, rather than balanced, well-formed and robust. Leaves are far too distant on the stalk, and the stem itself is too slim and often bending. This is technically called “etiolation”, it is very common too, but what causes it?

What causes leggy seedlings?

Leggy seedlings have two main causes:

  • Lack of light, so the seedling grows very fast trying to reach it as fast as possible, but it loses in strength. It’s like it’s “stretching its neck”. This is the most common cause of all.
  • Too much heat, which makes the seedlings feel uncomfortable, so they grow fast and sli in search of fresher air.

But now you know…

How can you avoid leggy seedlings?

First of all, if you are buying them – well, don’t! And if you have already purchased some, try to get them stronger with these methods. If instead you grow them from seed, start using these tips straight away!

5 Plant-Killing Mistakes to Avoid When Growing Seedlings and Transplanting Them in Your Garden 1
  • Give your seedlings enough light. As soon as you notice that they are getting too long and lanky, correct the exposure.
  • You can also use grow lights and other lighting systems, in which case, make sure that the source is not too far from your seedlings, but not too close to burn them. LED are cool, and you can place the about 1 foot away (30 cm) from your baby plants’ heads. With hot sources (bulbs etc.), check that the heat does not reach them.
  • Give your seedlings about 16 hours of light every day.
  • Use a gentle fan to refresh your seedlings with a breeze (not wind!), so that they feel cool, and never hot. This also trains them for when you transplant them into your garden.
  • Of course, check the room’s temperature constantly, making sure it is suitable for the seedling varieties you are growing there and…
  • Overall, the average germination temperature is between 68° and 84°F (20° to 29°C). But each variety has its own, so check it out here:
Temperature Range
Germination Temperature
Beans65°F – 85°F80°F
Beets50°F – 85°F85°F
Broccoli50°F – 85°F75°F
Brussels sprouts50°F – 85°F75°F
Cabbage50°F – 85°F75°F
Carrots50°F – 85°F75°F
Cauliflowers45°F – 85°F80°F
Collards45°F – 85°F75°F
Corn50°F – 90°F85°F
Cucumbers60°F – 90°F85°F
Eggplant60°F – 95°F85°F
Kale45°F – 85°F65°F
Kohlrabi45°F – 85°F80°F
Leek45°F – 95°F75°F
Lettuce40°F – 85°F75°F
Okra60°F – 90°F85°F
Onion45°F – 90°F75°F
Parsnip50°F – 85°F70°F
Pea40°F – 85°F75°F
Field peas65°F – 95°F85°F
Peppers65°F – 95°F85°F
Peanut65°F – 85°F80°F
Pumpkin70°F – 95°F85°F
Radish55°F – 85°F65°F
Spinach40°F – 75°F65°F
Summer squash60°F – 95°F85°F
Swiss chard40°F – 95°F80°F
Tomato60°F – 95°F85°F
Turnip45°F – 85°F65°F
Watermelon65°F – 95°F90°F
  • But careful, the average ideal temperature for seedlings is 10°F below that of germination!
  • So, once the seeds have germinated, turn down the heating!

Mistake Nr 2 – Transplanting Seedlings too Early

We are all eager to transplant our seedlings as early as possible, so we can get a longer harvest season, but it is risky, and it can be counterproductive. If the weather is still too cold, you may lose them all!

Transplanting Seedlings too Early

To avoid jumpstarting your seedlings, you must make sure that you plant each veggie variety when it is safe, and, as a general rule, it’s best to wait a couple of weeks on the safe side. In fact, even if temperatures have reached good levels for your lettuce rather than eggplant or kale, the odd frost or cold day may still occur, especially in cooler climate zones.

You can get a planting calendar, but you need to make sure that it is specific to your USDA hardiness zone. But there are also other ways to make sure…

But there is another tool you can use, and it is called “phenology”… Look at which plants are blooming, and you will know which seedlings are safe to transplant! They know if the weather is fine.

For example, if lilacs are in full bloom, you can plant squash, while tomatoes are safe to plant when lily of the valley is flowering.

If you want to know more and have a more complete list, check out our article of phenology here!

Mistake Nr 3 – Overwatering Your Seedlings

Overwatering is one of the most common mistakes inexperienced gardeners make, also when it comes to seedlings. Forgivable because it is too much love, but you risk suffocating their roots!

 Overwatering Your Seedlings

Yes, because plant roots also need oxygen, and, if the soil is packed with water, they can’t get it.

When you water them (before or after transplanting), the soil must be moist, but not soggy. You don’t want it to be like “mud”. As an exercise, water some soil till it gets humid, and squeeze it. You should only get a few drops out of it. If so, it still has air. But if it drops lots of water and easily, then it’s not good at all.

What’s the best way to water seedlings?

OK, so, how can you water your seedlings so they have just enough water?

  • First of all, wait till the seedling pots are light when you lift them and that the top 1 inch (2.5 cm) is dry.
  • Next, pour some water into the trays.
  • After this, water the seedlings from above.
  • Then wait for 2 to 3 hours.
  • Finally empty the trays.

Mistake Nr 4 – Transplanting Seedlings at the Wrong Time of Day

I understand the temptation to plant your seedlings in the morning, but it’s really the wrong tie of the day! If you do, they will suffer the heat of midday, water will evaporate, and they will get a bigger transplant shock!

5 Plant-Killing Mistakes to Avoid When Growing Seedlings and Transplanting Them in Your Garden 2

Instead, transplant your seedlings in the evening, when temperatures are cooler, and water does not evaporate as much. What’s more, at night they “rest”, their metabolism is slower, so, they have more time to acclimatize to their new “home”.

The only exception is if it’s a cool, cloudy and – even better – drizzling day. In this case, any tie is good.

Mistake Nr 5 – Not Hardening Your Seedlings Before Transplanting Them

5 Plant-Killing Mistakes to Avoid When Growing Seedlings and Transplanting Them in Your Garden 3

Your seedlings have grown up in a sheltered and comfortable environment, with steady temperatures, humidity, light and no strong winds. If you move them outside, they are not ready fore these weather conditions, and this gives them shock.

This is especially true in colder climate regions. So, if you want to avoid this transplant shock, you need to harden your seedlings beforehand.

5 Plant-Killing Mistakes to Avoid When Growing Seedlings and Transplanting Them in Your Garden 4

So, move them outside little by little.

First, take them out in a part shade and sheltered position, for an hour or two, in the afternoon. Then a bit longer, and again, till you feel safe and they have hardened enough to live in your vegetable garden without “coming back indoors” even at night.

This process can take some time, and you only keep seedlings for a few weeks overall. So, start early, with very short periods of time, so, when the day to transplant them comes, they will be ready and strong.

Treat Your Seedlings Well and Your Vegetable Garden Will Give You a Long and Bountiful Season of Healthy Crops

Transplanting seedlings is a delicate moment in their life, because it is a shock for them. Avoid these five mistakes and you will give them and your vegetable garden, the best possible start. And a final tip… After they have moved to their new home, check that they become sturdy rather than spindly and protect them from pests, snails and slugs, especially if they have tender leaves, and, if you want a few ideas on how, we have an article for to help you along…

Amber Noyes

Written By

Amber Noyes

Amber Noyes was born and raised in a suburban California town, San Mateo. She holds a master’s degree in horticulture from the University of California as well as a BS in Biology from the University of San Francisco. With experience working on an organic farm, water conservation research, farmers’ markets, and plant nursery, she understands what makes plants thrive and how we can better understand the connection between microclimate and plant health. When she’s not on the land, Amber loves informing people of new ideas/things related to gardening, especially organic gardening, houseplants, and growing plants in a small space.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.