Hardening off seedlings

When you start your seeds indoors, you will eventually want to move them outside. To do this for the best success, hardening off the seedlings is highly recommended.

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Starting seeds indoors

In many parts of the country, it is beneficial to start your seeds before the last frost date when you can plant outdoors. In some areas, it is required if you want to grow many of the standard crops such as tomatoes, cucumbers and squash.

Related article: what to grow if you have a brown thumb

The longer growing plants need more time to mature in order to provide a crop. These warm weather crops also cannot handle a late freeze but need a long time to grow fruits. In many cases, it is common to need 100 or more days to maturity, such as with cushaw squash. In this case, you will want to start your seeds indoors.

Simple seed starting set up

All you need is some grow special seed starting mix, containers, seeds, water and some kind of light. Its also beneficial if you have a small fan as well. The fan and light are needed to grow strong, healthy seedlings. Problems with starting seeds indoors are common, particularly leggy, weak seedlings. You can see more about trouble shooting here.

What is hardening off?

Hardening off seedlings is the process in which you are slowly exposing your indoor seedlings to the outside. The power of the sun and all of the elements (wind, rain, weather, drought, etc.) will be much harder on your seedlings that the sheltered, controlled environment of the indoors. To get them to acclimated, many gardeners put them through a process known as hardening off.

How to harden off seedlings?

There are a few basic things to keep in mind when hardening off any seedlings you have started indoors. First, they are not used to the strength of sunshine. Even in more northern latitudes, the sun will always be more powerful than indoor grow lights. If you live in the southern part of the US, this might be too intense for your baby seedlings.

Related article: Gardening in the south

Depending on where you live and when you start the moving process outdoors, you may need to consider shadier spots than in direct, especially hot, sunlight that could burn the seedlings. Also, the sun and wind, will naturally dry out the soil faster. This is less of a problem when they are transplanted into the ground or raised beds, but might be an issues in pots and small growing trays.

Steps to hardening off seedlings

Keep in mind when hardening off your seedlings you don’t want them to be too crowded in their original space. You may need to transplant your seedlings into bigger containers in order to allow them to adjust to the soil and being outdoors. Too much stress on the plants is bad but a little stress can make plants more resilient.

1. First week – take well watered and strong seedlings out for just a couple of hours on a cloudy day when the temperature is not too low or high and the wind is not too strong.
2. Second week – leave the seedlings out for up to 5 hours, but bringing them in during cold snaps or inclement weather
3. Third week – leave seedlings out all day, bringing them in at night for a little extra time under grow lights
4. Fourth week – leave them out 24 hours a day, rain or shine
5. Fifth week – plant them out into pots, raised beds or the ground with a little compost

When you finally plant them out, you can use a cloche. You can have a dedicated cloche or you can just reuse the tops of milk jugs or large soda bottles. Or anything else you have on site that might protect your plants. This will be especially important if a sudden change in weather occurs right after you’ve planted.

All plants go through a brief period of shock once transplanted because you are moving them from one soil to another and the roots and plant need to adjust. Because of this, you only want to do this one or twice, depending on your seed starting set up. Once in their final home, it is best to leave them be to adjust.

Be sure to keep the are free of weeds or mulch well as they are still seedlings and will need support for a while. At this point you can also fertilize or add compost to help the delicate roots do well in their new environment.

Other tips and planting out

When planting out your seedlings, make sure to be delicate. They may not be as hardy as seeds started outdoors. Protect cool weather crops you started indoors with shade or wind cover, especially if planting closer to the end of spring or during a warm spell. This is particularly important if you are starting seeds for a fall crop. These seeds are usually started during the high heat of summer.

For seedlings that animals might munch on, aim to provide some protection. Also, watch the weather. Don’t plant out when a large storm is coming or has just past. You want the soil to be moist but not saturated. You also don’t want to drown your baby seedlings with a big storm with lots of rain.

If an adverse weather even occurs during the hardening off period, just pause for the day and start out again the next day or when the weather improves. If you can, try to put the seedlings in a semi protected spot outdoors like a cold frame, covered porch or green house. All these options offer different kinds of protection that will give your seedlings the best start.

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