When to transplant weed seedlings from seed tray

5 Signs It’s Time To Repot Your Seedlings

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It’s important to be able to recognize when it’s time to transplant seedlings from the seed tray to a larger pot. Transplanting seedlings a few weeks after starting should be part of your seed starting routine.

We start the seeds in smaller containers because we can control moisture and temperature much better that way, and if you’ve heard me talk much about seed starting then you know my motto is that moisture and temperature are the most important factors in getting good germination.

But once the seeds sprout, they quickly outgrow their seed starting container. It would be a bad idea to let them continue to grow in a pot that is too small. They’ll become nutrient deprived and their roots will grow round and round into a big knot.

Transplanting them into larger pots, helps them develop healthier roots and grow faster. By not restraining their growth indoors, you’re training them to grow big and strong when it’s time to put them in the garden.

But how do you know when to repot seedlings?

There are a few simple things you can look for that are dead giveaways your plants need a bigger pot.

1. They have one or two sets of true leaves

The ideal time for transplanting your seedlings is about 3 weeks after they sprout or when you have 1-2 sets of true leaves. It’s better to get them in new containers before they start to show the signs of stress listed below.

2. The cotyledons are turning yellow and falling off

Cotyledons are the first leaves that emerge from a seed. They are different than the “true leaves.” True leaves are the second and subsequent sets of leaves that grow after the cotyledons emerge.

It is normal for cotyledons to yellow and fall off, but if they’re doing it when you only have 1 or 2 sets of leaves, your plants really need to be transplanted.

3. The true leaves are turning yellow

It’s definitely time to transplant if the true leaves are yellow. This is a sure sign that your plants are starved for nutrients.

4. The roots are wound around and around the root ball

You definitely want to see roots in your growing medium when it’s time to plant, but if they’re circling around the edges of the root ball, then they’re getting too crowded.

5. They’re crowded

You don’t want to overcrowd your plants when they’re young. Some plants will grow taller than others and that will affect how much light the others get. You’ll also get the larger plants sequestering all the nutrients and that will stunt the growth of your other plants as well.

Why transplant the seedlings at all?

You might wonder why we would go to the trouble of repotting seedlings at all? Why not just give them some fertilizer, or better yet, start them in a larger container to begin with?

You’ll be much more successful germinating seeds if you start them in small containers. This allows you to have more control over the temperature and moisture in the seed starting container. We’ve found we have much better sprout rates in the smaller cell trays as compared to using other types of seed starting containers.

You can dose your plants with some fertilizer but that will stimulate growth. They’re already telling you they need more space, why stress them by making them grow bigger in the same small space?

Both of those options are viable alternatives, but you’ll have healthier plants if you transplant instead.

How to repot seedlings

Transplanting seedlings is quite easy to do. You simply need a new container and some potting mix. We recommend a container that is twice as big as what they are in now and a high quality potting mix like Fox Farm Ocean Forest.

We like to mix the potting mix and the seed starting mix in a 50:50 ratio. This is especially helpful for young seedlings who still have tender roots.

Before filling your containers, wet down your soil mixture to ensure even watering after you plant. Then nest your seedling in the new container, filling in around the base of the plant and pressing down to seat it in well and remove air pockets.

For tomatoes, bury the stem leaving only 1 or 2 sets of leaves above the soil line. For all others, plant them level or bury the stem about 1/4 inch or less.

Water your transplanted seedlings well and place them back under the light.

What about fertilizing seedlings?

You can fertilize young seedlings after transplanting as needed. Use a liquid organic fertilizer diluted to half strength. If they tolerate the half strength and seem like they need more, you can up it to full strength.

Don’t fertilize your seedlings until after you transplant them. You don’t want to stimulate growth in a space that is too small.

How and when to transplant cannabis plants

Transplanting is the process of “re-homing” a cannabis plant, or moving a plant into a bigger pot with more soil as it grows bigger.

Growers typically start off the cannabis growing process by planting many seeds in small pots because they don’t know if all of them will sprout—or germinate—and they don’t know if all of them will be female.

Only female cannabis plants produce buds, so if you start growing from regular seeds, you will have to sex them out and discard the males.

Why is transplanting marijuana plants important?

Transplanting gives a marijuana plant’s root system more space to spread out, allowing the plant to grow healthy and strong and to flourish.

When roots become cramped and can’t spread out they can get tangled and become “rootbound”—this will effective choke the plant, leading to a stunted, sickly plant, and can even kill it. A healthy root system will lead to a healthy weed plant.

A plant’s container will determine how much the roots can stretch out, and therefore how big your plant will get. A container that’s too small will stunt it.

You don’t want to plant a seed in a giant pot because you could potentially waste soil if the seed doesn’t make it. Also, if growing weed outdoors, it’s hard to plan out a garden and where to put your seeds in the ground if some seeds don’t make it.

Most weed growers start seeds in small 4-inch or 1-gallon pots when germinating.

For the seeds that do make it, they will need bigger homes after several weeks of growing and will need to be transplanted either into a bigger pot or directly into the ground.

When planting into the ground, make sure not to crowd your plants so their roots don’t run into each other.

The symptoms of a rootbound plant include:

  • Flimsy new growth
  • Stunted flower production
  • Stem discoloration (reddening)
  • Nutrient sensitivity

A rootbound plant may also appear under-watered. If a plant requires watering more than once a day, it may need to get transplanted.

When to transplant marijuana

Check out Johanna’s full video series on how to grow weed on Leafly’s YouTube .

Most marijuana plants go through 1-2 transplants during their life but could have more. As an example, transplanting can happen from:

  • First container (1-gallon) to second container (2-gallon): 4-8 weeks after seed germination
  • Second container (2-gallon) to third container (5-gallon): transplant 8-12 weeks later, or 2 weeks before flowering

Some growers may only transplant once: using the example above, from a 1-gallon to a 5-gallon container, skipping the 2-gallon. And depending on how big you want your weed plants to get, you may transplant into bigger pots than what’s listed above.

The same goes for transplanting outside, in the ground—you can go straight from the first pot into the ground, but it depends on when you transplant and your local climate and weather.

Here are some indicators that your cannabis is ready for a new container.

Number of leaves

Young plants sowed in small containers are usually ready to be transplanted after they’ve sprouted 4-5 sets of leaves, but keep in mind this may vary from strain to strain.

Root development

Check the drainage holes at the bottom of the container—a plant should have a healthy and visibly white root system. If roots are growing out of the holes, it’s time to transplant.

Any discoloration or darkening may indicate the plant has become rootbound and a transplant should take place immediately.

End of vegetative stage

A weed plant should be in its final pot or in the ground with plenty of room for its roots before it enters the flowering stage. During flowering, a plant will increase in both size and volume, as the plant itself continues to grow and as buds develop. It will require a substantial amount of space for root development.

How much space does a marijuana plant need?

Plant height (inches) Pot size
0-6″ 4-inch (16 oz.)
6-12″ 1-gallon
12-24″ 3-gallon
24-42″ 5-gallon
42-60″ 10-gallon
60-84″ 20-gallon

When transplanting cannabis, give the plant at least double the space of its previous container. This reduces the number of times you need to transplant and minimizes the risk of transplant shock, which may occur when a plant experiences extreme stress from root disturbance.

For example, you could go from a 1-gallon to a 2-gallon to a 5-gallon, or from a 2-gallon to a 5-gallon to a 10-gallon.

Medium-sized indoor cannabis plants tend to be fine in 5-gallon containers as a finishing pot. Large outdoor plants may require much bigger containers to reach their behemoth potential, sometimes up to 10- or 20-gallon pots.

When in doubt, always opt for slightly more space than needed. A plant tends to require 2 gallons of soil for every 12 inches of growth it achieves during the vegetative stage. Knowing the potential height of the strain you’re growing is helpful.

Why not start in the largest pot for your marijuana plant?

Growers typically transplant weed plants 1-3 times, moving plants to bigger pots gradually as they get bigger.

If a plant is put in too big of a pot, the roots won’t stretch out that much and won’t soak up as much water. This can cause water to sit in the pot for a long time, waterlogging the plant and leading to root rot.

You can transplant into the largest pot for your weed plant to avoid multiple transplants, but be careful not to water all of the soil—only water around the stalk of the plant where the young roots are.

How to transplant marijuana

Check out Johanna’s full video series on how to grow weed on Leafly’s YouTube .

The process of transplanting weed does not come without risk. Transplant shock can be incredibly detrimental to the growth and development of a cannabis plant, and can even kill it. However, through proper execution, the process of transplanting will benefit the plant and lead to stronger root development and healthier flower production.

First transplant of a cannabis plant

Young cannabis plants should start in a 4-inch or 1-gallon pot. This starting pot should be adequate for a few weeks before transplanting is needed.

Again, the first transplanting should occur after the seedling has sprouted its 4th or 5th set of leaves. To transplant:

  • Wash your hands and/or wear gloves to prevent contamination of the delicate roots, and keep the surroundings as sanitary as possible.
  • Give the plant a light sprinkling of water to help minimize shock; don’t drench it, as the soil will be difficult to work with.
  • Fill the receiving pot with soil, allowing enough space for the new plant.
  • Avoid overpacking the soil during and after transplanting—this can compromise drainage and damage the root system.
  • Do not disturb or damage the roots when transplanting; the first transplanting poses the greatest risk for shock, which can occur from root damage and agitation.
  • Avoid intense light when transplanting; this will help prevent transplant shock as well.
  • Fully water in the plant once it’s in its new home.

Additional transplanting of cannabis plants

You may need to transplant your weed plant a second or third time to maximize its growing potential. Always monitor plants for symptoms of distress or overcrowded roots.

To do so, follow the steps above, and make sure the new container is at least twice as big as the old one, if not bigger.

The finishing container is the final home of a plant until it’s harvested. This will be the largest container for a plant, and you always want to transplant into this pot 1-2 weeks before the flowering stage—you don’t want to disturb a plant while it’s flowering.

Keep in mind that large plants may require stakes or other support to avoid structural damage after transplanting.

When to Transplant Seedlings from Seed Tray

It’s very rewarding to raise your fruits, vegetables, and herbs from infancy by starting them inside in a seed tray and then transplanting them into their more permanent pots or beds. Seedlings are fragile beings, however, and the timing of your transplant can spell the difference between flourishing and failing.

You’ll want to transplant your seedlings soon after they’ve grown their “true” leaves, which will develop after the “seed” leaves. Transplant when the weather is mild, and be sure to allow about a week of “hardening off”, so your seedling can adapt to its new environment.

When to transplant seedlings from seed tray

Mastering all the variables in transplanting your seedlings can be tricky, but is crucial to the future success of your seedlings.

Nailing this delicate transition period will set up your seedlings for growth and success, saving you time, money, and frustration in the future!

Picking the Perfect Time

Identifying your Leaves

While your seedlings are growing in their tray, keep a close eye on the leaves they’re developing.

There are two different kinds:

  • seed leaves (or cotyledons)
  • true leaves

Identifying these two kinds of leaves is critical for knowing when your seedling is mature enough to be moved.

  • May not even be visible on some kinds of plants!
  • E.G. Green peas, corn, mangos
  • If visible, they will be simple and smooth looking, quite different than the leaves of an adult plant
  • May appear as a pair or individually
  • Are usually near the base of the stem
  • Store nutrients for the seedling, like the plant version of an egg yolk
  • Will appear after the seed leaves
  • Look like miniature versions of the adult plant’s leaves, with unique shapes, ridges, and hairs
  • All leaves that form after the first set of true leaves will be identical to it/them and to each other
  • Perform photosynthesis for the plant

The appearance of true leaves is the signal that your plant is nearly ready for transplant, and that it’s time to begin hardening off!

Seedlings with cotyledons and true leaves

Hardening off

Hardening off is a 7-10 day process where you gradually increase your plant’s exposure to outside conditions.

The process of hardening off gives your seedling the time it needs to adapt to its new environment and be prepared for its post-transplant life.

Transplanting without hardening off can shock your seedling’s system, and put it at major risk

On the first day, put it outside for 2-3 hours in a shady area with limited exposure to the wind.

The next day, leave it out for 3-4 hours in slightly more intense sunlight, and so on.

During the last couple of days, make sure that your seedling stays outside overnight to get acclimated to the cooler twilight temperatures.

If the weather is bad on one of your hardening off days, like in the case of a rainstorm or cold snap, delay hardening off until things calm down.

Weather Conditions

When the big moment arrives, and you’re finally ready to move your seedling to its outdoor home, try to pick a day with relatively mild weather.

Your seedling will be in a state of confusion right after the transplant, and anything you can do to make the transition a gentle one will increase its chance for success.

Here are some tips for keeping things nice and easy:

  • Check your local vegetable planting calendar to find the ideal transplant dates for your specific plant
    • Try to first plant your seedlings in their trays 6-8 weeks before this date, so they have plenty of time to grow

    NOTE: Some species of plants should NOT be started inside in seed trays, but instead directly seeded outside in your garden or greenhouse.

    Plants more suited to direct seeding are usually hardier and grow more quickly than those which do well starting in a seed tray.

    Examples include for each kind include:

    Direct seeding Seeding in tray
    Collard Greens

    If everything goes perfectly, you should have large, healthy, hardened-off seedlings with well-developed true leaves right around the recommended date to transplant.

    Yet as you may know, adventures in gardening rarely go completely as planned.

    So, here are a few more good decisions you can make to give your seedlings the best chance at life you can.

    Transplanting Tips: What kind of soil should I use?

    In the Seed Tray

    If you’ve been taking notes, you may remember that seedlings get the nutrients they need from their seed leaves.

    Instead, go for something that’s light and well aerated, so that the roots of your seedling have plenty of room to stretch and grow.

    You’ll want to make sure that the soil you use is classified as sterilized, meaning its been treated to be as free from contamination as possible.

    Disease Prevention

    Sterilized soil is important, since even a small amount of mold or fungus can do major damage to a tender young seedling.

    During your plant’s infancy, a top priority should be keeping it totally disease free, and your soil should reflect that.

    You can actually get what’s called soil-less starting mix, commonly made from things like peat moss, sand, or bark, which lets you be completely sure your “soil” is as clean as can be.

    But be aware that this will need to be changed out for the real deal when you move your seedlings out of the tray.

    Once Transplanted

    Light and well aerated potting soil is the best kind for your seedlings to be transplanted into, as well.

    It’s easy to find soils specialized for this purpose online or at your local garden supply store.

    Again, keeping things as gentle as possible during the transition period will give your seedlings the best shot at success.

    Once planted, water the soil to the point where it becomes damp but not soaked.

    Adding fertilizer to the planting area can be helpful, but only use it at half strength so as not to overwhelm the seedling.

    Moving your seedlings safely

    Technique: how to do it

    The actual, physical process of moving your seedling from the seed tray is rife with danger.

    The most important thing to keep in mind is DO NOT grab the seedlings by the stems! This is an excellent way to damage or even break the stems.

    Instead, un-pot your seedlings by turning them upside down and gently tapping the bottom to remove the whole thing at once.

    Do your best to keep the soil and roots intact. If the soil kind of sticks to the inside of the pot, you can use a quarter to help ease it out.

    Are the seedling’s roots wrapped around the soil in a twisted spaghetti fashion?

    Then carefully unwind them so the roots are all facing outward. This allows the roots to spread more easily once transplanted.

    Hole Size

    The hole you dig in your planting area should be shallow enough to allow the seed leaves to be above ground (if present).

    If you’ve been using a biodegradable pot, like a peat pot, the process is much easier.

    Simply dig an appropriate sized hole in your bed, and fully immerse your pot in the soil.

    Don’t leave any part of the pot above ground, as this can lead to a drying out of your plant very quickly.

    Thinning out Seedlings

    What is it and why should I do it?

    Thinning seedlings is the act of removing certain individuals from the seed tray or planting bed/pot.

    Thinning seedlings is best done when the seedlings grow too close together and become so crowded that none of them can grow properly.

    It might seem counter-intuitive (and not a little depressing) to effectively kill one of the seedlings that you’ve worked so hard to raise.

    But the competition that overcrowding causes can easily stunt the growth of your whole crop.

    When to Thin Out Seedlings

    Knowing if, when, and how much you need to thin out your seedlings requires a bit of thought.

    When they’re still in their seed trays, it’s pretty straightforward: Keep it down to one seedling per cell.

    For seedlings that were planted directly into the garden, there should be instructions on your seed packet which lay out the space requirements for your seedlings.

    Thinning Technique

    Do the deed using a pair of micro-tipped pruning snips, or even just a small pair of scissors, well sterilized with rubbing alcohol beforehand.

    Cut the seedlings near the base of the stem, but leave the roots alone, or you could risk damaging the roots of nearby plants.

    Look for and thin out the weakest looking seedlings, leaving the stronger looking ones alone.

    If you’re not sure which seedlings are the healthier ones, then just thin them at random.

    It’s best to thin your seedlings as early as possible, so as to allow the survivors as much unimpeded growth as possible.

    Related Questions

    Can I Make my Own Seed Trays?

    You can easily find seed trays online or at your local garden supply store.

    But for economically-minded gardeners, there are some common household items you can use that work just as well!