Hardening off is the process of bringing your seedlings from the indoors to the outdoors, in a way that doesn’t stress them out.

You do not need a greenhouse to do this, and within a week you can get your seedlings out of your house and into your garden safely.

Here I go into a day-by-day guide to harden off your seedlings without the use of a greenhouse!

Let’s Dive In…

Hardening off Seedlings without a Greenhouse in a week

Usually, this hardening off process starts just before or after your average last frost date in your area.

Some plants that can be transplant prior to that final frost date include kale, cabbage, broccoli, cilantro, parsley, peas, lupines, snapdragons, and radishes.

However, please judge that gingerly since these plants can take a frost but not a freeze.

Most vegetables or flowers need frost free nights.

Tools You Need

Table, or area of patio/decking/garden where it can be left undisturbed.

Umbrellas, sheets, or totes.

Steps to Take Day by Day

Day 1: Start on a warm day. Find a shady spot or create shade with umbrellas, tables, or even totes flipped on their side. Allow the seedlings to spend 2-6 hours outdoors in the shade on day 1. Bring inside overnight.
Day 2: Repeat the process on day 2, keeping the plants in the shade, except extend the time outside to 12 hours. Bring inside overnight.
Day 3: Repeat the process of letting the seedlings sit in the shade, however, if there is no frost in the forecast, allow your plants to spend the night outside. Water if necessary.
Day 4: Start allowing some sunlight to get to them. Morning or evening light is best for the first day to avoid sun burnt leaves. Let them stay outside overnight.
Day5: Allow them to sit in the sunlight a little bit longer, depending on how your plants are looking. If they are looking pale, and sun burnt, just let them sit in the shade to recover for an extra day. If it’s a cloudy day, and your plants looks strong, go ahead and let them sit in the overcast sun all day. Outside overnight.
Day 6: Extend the time they get sunlight even more. Making sure they are watered at this point too. Some weak liquid fertilizer also helps on this day to get them prepared for transplanting. If your seedlings are looking good, let them sit in dappled shade like under another larger plant during high noon. Outside overnight.
Day 7: See if you can let them sit in the direct sun all day. Sun burnt leaves look pale, and weak. If you notice this, just let them sit in the shade for a couple hours during the day. They will recover. But you should be close to transplanting them, so they need to start sitting in the high noon sun. If going well, you should see a burst of growth by now also.
Day 8 and beyond: Give or take a few days, you should be able to transplant seedlings at this point in time. You know your plants are ready to go when they are unaffected by sun and temperatures, look dark green, and have shown some growth over the past week. Most seedlings only take about a week to acclimate to outdoor weather, unless they were sun burnt early on. If sunburnt, wait a few more days until you transplant them so they can recover.

Pro tips:

Weak liquid fertilizers help with transplant shock on Day 8 or beyond. This can be basic, homemade compost fertilizers or a storebought brand.

Please make sure they are watered! Sunlight tends to evaporate the water faster than grow lights.

Transplant the whole seed block (seed soil and all). Do not prick out the seedling to transplant into the garden. This will also help with transplant shock and reduce root damage.

They can sit outside before being transplanted for a while if you need to wait.

Why harden off your seedlings?

You need to harden off your seedlings so they don’t go into transplant shock and die off.

Younger seedlings tend to do worse than older seedlings. That’s why it’s nice to start seed early in the winter/spring time so you have larger plants to transplant later.

Seedlings from the nursery also need to harden off, unless you noticed that they were sold completely outside. This is usually not the case, however, so following these steps with storebought seedlings can help avoid transplant shock also.