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Starting Plants Indoors for Outdoor Growing

By Rich Hamilton | Last updated: April 25, 2021
Key Takeaways

Even if you are a veteran outdoor gardener, there are benefits to using some indoor growing techniques to get a jump on your outdoor growing schedule.

Starting seeds off indoors allows you to use all the environmental controls of a growroom to manipulate conditions such as light, temperature, and humidity to give your plants the optimal conditions for success. Doing so will give your plants a head start, creating a root network healthy and robust enough to provide them with the best chance of survival when they are out in the open as nature intended.

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Sowing your seeds indoors offers many benefits. The first is it allows you to start your growing season much earlier. You will find you can fit in more grow cycles per season while also growing long-season crops such as tomatoes, broccoli, peppers, and kale in short-season climates.

If the natural climate where you live is unpredictable, seeds sown directly outdoors may struggle to survive and are at the mercy of weather changes. If you started them off under controlled conditions indoors, however, then you should find they will be strong enough to tolerate some environmental fluctuations when you transfer them to an outside garden.

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If you sow your seeds indoors, early in the season, it allows you to be more selective with the seedlings you decide to take through to harvest. You can plant many seeds and then wait to identify the strongest, healthiest looking contenders for transplant outdoors. Doing this will hopefully increase your chances of success and high yields. (Read: How to Prime Seeds for a Head Start on the Grow Season)

This method doesn’t suit all types of plants, and some seeds are better sown directly outdoors including pumpkins, cucumbers, squash, and watermelon. Root vegetables like carrots and beets do not like having their roots disturbed and are resistant to transplanting. Plants with long taproots like parsley and dill are also not suitable for transplant, so always check before you sow.

So once you have started your seeds off indoors, what's the next step? And how do you move them outdoors successfully?

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Tomato seedlings growing in cups on a window sill.Sowing your seeds indoors offers many benefits.

Hardening Off Indoor Seedlings

Inexperienced gardeners often find themselves disillusioned when the seedlings they have lovingly nurtured inside for weeks deteriorate very quickly on introduction to an outside environment.

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Successful transitioning of seeds from indoors to outdoors relies on the process of hardening off, which is where your seedlings are toughened up gradually to their new climate before they are fully transplanted.

To harden off any annual plants, including vegetables or flowers you would plant in spring, there are a few steps that you should follow. (Read: How to Transplant and Harden Off Cannabis Plants for Outdoor Growing)

Firstly, move your seedlings somewhere outside that is shaded from the sun and sheltered from the wind. You need to do this for increasing periods each day. Your plants will be weak and prone to breakage at this point as they will not have been exposed to the wind yet. Increase the exposure time by an hour or two a day until your plants can withstand outdoor conditions for a full day. If your seedlings begin to wilt at any stage of the acclimation process, move them back to a shadier spot or indoors if this happens very early on.

When first introducing your plants to the outdoors, you should thoroughly water them to prevent them from drying out. As they spend increasing amounts of time outside, you should reduce watering until you leave the soil damp only.

Once you have reached the point where your plants can stand to spend a whole day outside, they are ready to be exposed to a bit more sunshine.

Move them into direct sunlight for two to three hours at a time. You should keep a close eye on the leaves and look for any changes. Bleached-looking spots on leaves can signal sunburn, which can be fatal for seedlings.

Once your plants can withstand a full day in the sun, then you are ready to transplant them into your outdoor garden.

Young tomato plants growing outdoors in a raised garden bed.Weather is the biggest threat to delicate seedlings so you should carefully plan when to transplant them.

Transplanting to the Outdoors

If you have many seedlings to transplant, then an auger tool or garden drill is an excellent buy to save time and reduce the strain of hours spent on your knees, crouched over, digging small holes with a trowel. Augers come in different sizes, but a 3-inch one will usually suffice for everything from small annual plugs to larger vegetables.

When you turn your seedlings out from their pots, be as gentle as possible to cause minimal disruption and stress to the roots. Place your hand over the surface of the pot with the seedling stem between your fingers. Flip the pot over and with your other hand give it a few firm pats until the seedling, soil, and roots come away from the pot as one entity. Think about how you would turn a sandcastle out of a bucket and you will get the idea. It would help if you had the planting hole ready to carefully slide the seedling into straight away and then cover it with your chosen growing media. Please do not press the media too firmly as this will remove essential oxygen from it. If you are using bio-degradable pots or stonewool, you can plant the seedling right into the new medium.

Once you have transplanted the seedlings, even though you have been steadily acclimatizing them to the sunshine and outdoor conditions, you should still keep them shaded for the next three to five days.

Shading the seedlings protects them from the threat of transplant shock which can cause your plants to wilt following transplanting.

Once out in the open, the weather is the biggest threat to delicate seedlings so you should carefully plan when you are transplanting them and ensure that it is not too early in the season. If your timing is correct, but you still experience unexpected cold snaps or frost, then cover your seedlings with pots or anything you have on hand to protect them and keep them a little warmer overnight and early in the morning.

If it suits the crops you are growing, then starting your seeds in an indoor environment will give you a jump start on your outdoor gardening endeavors. It provides your plants with the best of both worlds: a controlled start where you set them up to develop a robust root system and subsequent healthy growth foundations. Following this, when you harden them off and transplant with care to the outside natural environment, they can drink in all the elements and nutrients the garden has to offer and thrive as nature intended — resulting in more robust, healthier, and productive plants. (Read: Same but Different: Indoor vs. Outdoor Nutrients)

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Written by Rich Hamilton | Writer, Consultant, Author of The Growers Guide

Profile Picture of Rich Hamilton

Rich Hamilton has been in the hydroponics industry for more than 20 years, working originally as a general manager in a hydroponics retail outlet before becoming an account manager at Century Growsystems. He enjoys working on a daily basis with shop owners, manufacturers, distributors, and end users to develop premium products.

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