By Harris Seeds Guest Growing Partner, Tom Stokes Harlow
Greetings, fellow growers. You’ve taken on the rewarding challenge of raising plants, and now you’re looking at expanding your offerings by adding seedlings to your lineup. That’s a smart move. Seedlings are the bridge between seeds and market-ready plants, and they’re one of the most in-demand products among both home gardeners and wholesale buyers. Learn more about our plug and liner program for wholesale seedlings here.)
But here’s the catch: seedlings are delicate little creatures. They can thrive beautifully under your care, or they can sulk, stall, or even fail if they don’t get the right attention during transplanting. That’s why learning when and how to transplant seedlings—whether into bigger pots or into the great outdoors—is one of the most important skills you can master as a grower.
I’ve been at this long enough to have made (and learned from) nearly every mistake in the book. And I’d like to share what I’ve learned with you, so you can avoid those pitfalls and feel confident as you add seedlings to your offerings.
Let’s take it step by step.
Why Transplanting Matters
Think of seedlings like teenagers: full of potential, but in a stage where the right environment makes all the difference. Transplanting is simply moving a seedling from one container or location to another, giving it more space, nutrients, and resources to keep growing.
If you leave seedlings in their starter trays too long, the roots run out of room, becoming what we call “root bound.” When that happens, growth slows down, leaves may turn yellow, and the seedling can stay permanently stunted—even after being planted in the field. Yikes.
On the other hand, if you transplant too early, before the roots have had time to develop, you risk damaging fragile seedlings that aren’t yet strong enough to handle the move. Timing and technique are everything.
Steps in Transplanting Seedlings
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Every successful transplant begins with preparation. Here’s the general flow I recommend:
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Prepare your materials
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Have your larger pots or planting beds ready before you touch the seedlings.
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Fill containers about three-quarters full with a pre-moistened potting soil mix. (We’ll cover this in more detail in a bit.)
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Water seedlings before transplanting
A well-watered seedling is less stressed during transplanting. Dry roots are brittle and prone to damage, while moist roots slide into new soil more smoothly.
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Gently remove seedlings from their cells
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Loosen the soil in each cell by pressing on the bottom of the tray.
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Gently hold the seedling at the base of its stem (the crown), never the fragile top growth.
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Ease it out, roots and all.
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Plant into prepared holes
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Create a hole deep enough for the roots, but shallow enough that the stem stays exposed.
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Place the seedling in the hole, backfill gently, and tamp the soil lightly to remove air pockets.
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Water in
Give the seedlings a light watering to settle the soil around their roots. I always recommend using a seedling nozzle to prevent displacing the soil due to an overly strong spray.
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Aftercare
Provide steady moisture, airflow, (a simple household fan will do, or visit our greenhouse supplies website, Ken-Bar, for bigger operations), and (if indoors), provide supplemental light. This helps seedlings acclimate quickly and reduces transplant shock.
When to Transplant Seedlings into Bigger Pots
Here’s the million-dollar question: how do you know when it’s time to pot up seedlings into bigger containers?
Most seedlings spend 3–5 weeks in their initial trays before needing more space. Around that time, their roots begin to outgrow the small cells. If left too long, they’ll become root bound, which can spell trouble.
Signs it’s time to pot up:
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Roots poking out of the drainage holes.
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Slowed growth despite proper care.
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Leaves turning yellow or purple.
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Soil drying out too quickly after watering.
If you suspect root binding, check carefully. Look for purplish hues on the undersides of leaves (a sign of phosphorus deficiency caused by bound roots). If you find roots circling tightly around the plug when you pop a seedling out, it’s time to act.
The good news? If seedlings are still young (3–6 weeks), they can bounce back quickly once given space. The longer they’re left root bound, the harder it is for them to recover.
Moral of the story: don’t wait too long—pot up before seedlings hit that stressed, root-bound stage.
How to Transplant Seedlings After Germination
Let’s say you’ve just germinated a tray of seedlings. When should you move them?
The general rule: wait until seedlings have at least one set of “true leaves.” Cotyledons (the first leaves after germination) don’t count—they’re like baby teeth, temporary and fragile. True leaves are the first sign that your seedlings are actively photosynthesizing and ready for more room.
Here’s the process:
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Water seedlings gently a few hours before transplanting.
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Prepare your larger containers with moistened potting mix.
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Carefully tease seedlings out of their starter tray.
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Plant them at the same depth they were growing before.
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Water lightly to settle them in.
Remember: stems should stay exposed. Burying the crown can suffocate the plant and invite disease.
Examples of Transplanting Seedlings
Every crop is a little different. Here are some common examples:
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Tomatoes: These seedlings love being potted up. In fact, you can bury tomato stems a bit deeper than most plants—the buried portion will form extra roots, strengthening the plant.
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Brassicas (like broccoli and cabbage): These can be transplanted fairly young, as long as they’ve got their first true leaves.
Each crop has its quirks, but the core principles—gentle handling, proper depth, and watering in—apply to all.
Preparation of Seedlings Before Transplanting
Transplanting is easier on seedlings if they’re properly prepped. Think of it like getting ready for a big move—you don’t just pack up and go without a little planning.
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Moisten potting mix ahead of time
Use the “squeeze test”: grab a handful, squeeze tightly, and look for 2–3 drops of water. That means it’s saturated just right.
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Acclimate seedlings gradually
Mix up to 5% of your outdoor soil into the potting mix. This helps introduce seedlings to the microbes they’ll encounter outside.
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Choose the right containers
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Six-packs (606 or 806 trays) are great for small crops.
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2.5–4" pots are good for medium seedlings.
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Larger gallon containers work for perennials or bigger crops like tomatoes and peppers.
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Set up your environment
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Warm season crops may need a heat mat if temps are below 75°F.
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Provide supplemental light (12–16 hours daily).
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Ensure good airflow to prevent fungal diseases and to strengthen the plants. (Yes, the act of holding themselves upright in a blowing breeze actually gives them a nice little core resistance workout that builds up their internal stem structure, much like we build muscle).
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When to Transplant Seedlings Outside
Ah, the final step: moving your seedlings from their cozy indoor setup to the great outdoors. This is where a lot of new growers stumble—transplant too early, and you risk losing tender seedlings to frost, wind, or harsh sun.
Here’s what to consider:
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Frost-free date: Check your region’s average last frost date. Warm season crops (like tomatoes, peppers, and basil) should not go outside until after this date. Cool season crops (like broccoli and lettuce) can go out earlier.
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Soil temperature: Seeds may germinate in cooler soil, but seedlings thrive in warmer conditions. For example, tomatoes prefer soil above 60°F. (Invest in a good soil thermometer, you’ll thank yourself later.)
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Hardening off: Never skip this step. About a week before transplanting, start exposing seedlings to outdoor conditions gradually:
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Day 1: 1–2 hours outside in the shade.
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Day 2–3: A bit more sun and time outside.
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Day 4–6: Increase exposure daily.
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By the end of the week, seedlings should be spending full days outside.
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Hardening off toughens up seedlings, reduces transplant shock, and prepares them for the realities of outdoor life—wind, direct sun, and fluctuating temperatures.
Everyday Care After Transplanting
Once seedlings are potted up or planted outside, your job shifts to maintenance.
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Watering: Bottom watering works well indoors—set pots in a tray and let roots find the water. Outdoors, water deeply right after planting, then keep soil consistently moist (but not soggy).
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Airflow: Use fans indoors or space seedlings outdoors according to planting recommendations listed on the seed packet to reduce disease. Fungi thrives in air-deprived spaces. Harmful bugs are hard to spot and spread easily if plants are too clustered together.
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Light: Indoors, keep grow lights 12–24 inches above seedlings. Outdoors, full sun is best.
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Observation: Check daily. The best growers are keen observers—yellow leaves, drooping stems, or slowed growth are early signals that something needs adjusting.
Conclusion
Adding seedlings to your offerings is a wonderful step forward as a grower. Young plants are always in high demand, they showcase your skill and care, and they give customers the joy of taking home healthy young plants ready to flourish.
Transplanting seedlings—whether into bigger pots or into the ground—is one of those foundational skills that pays off for years to come. Pay attention to timing, prepare your seedlings well, and don’t rush the process. With a little care and observation, you’ll soon be raising strong, healthy plants that your customers (and your bottom line) will thank you for.
Remember: seedlings don’t stay small forever, and neither will your growing operation. Take it one step at a time, and before long, you’ll be looking back at these early days with a smile.
