Tag Archives: seedlings

How To: Harden Off Seedlings

We’re starting to transplant some of the more cold-hardy seedlings, such as cabbage, cauliflower, and broccoli, into the garden this week. Before we transplant any seedlings, we complete a process known as hardening off. 

In your home, your seedlings experience controlled climate conditions. They receive consistent light, moisture, temperature, and no wind. When we harden them off, we prepare them for the uncontrolled climate outside in the garden. If you skip hardening off, transplanting can shock your seedlings, meaning that they can stunted, fail to thrive, or die from the sudden changes. 

When and How to Harden Off Seedlings

Generally, we start hardening off seedlings one to two weeks before our ideal transplant date. Longer, slower hardening-off periods are usually better, so give it the full two weeks if you can. We start with just an hour or two of outside time each day and slowly increase that until the plants are ready to spend the whole day outdoors. 

Don’t place your seedlings outside on very windy days or when the temperature remains below 45°F. These conditions can shock even cold-hardy seedlings. 

Hardening Off Considerations

When we think about hardening off our seedlings, there are a few things we want to consider: sunlight, water, wind, and temperature. Below, we’ll dive into how to manage these factors as we harden off our seedlings. 


Your indoor lights are great for starting seedlings but aren’t as harsh as the natural sunlight your plants will face in the field. 

To begin hardening them off, set them out in a shady, sheltered location for one to two hours per day. Gradually move them to sunnier areas and increase the amount of time they spend outdoors. 


Plants in the field probably won’t receive the same consistent moisture they received under your watchful eye indoors. Occasionally, letting seedlings dry out but not wilt will help them adapt. tomato seedlings


Your tender seedlings have never dealt with any wind in your house. Start them outside in a sheltered location and avoid putting them out on very windy days. While your seedlings are still indoors, you can mimic the wind by gently brushing the tops with your hand.


Sticking seedlings out as soon as we’ve had a few warm days can be tempting, but you want to avoid damaging your plants. Don’t harden off seedlings when temperatures are below 45°F. Some plants will fail to produce if exposed to cold temperatures overnight. 

For example, broccoli may “button up” or only produce tiny heads if the seedlings experience temperatures below 20°F. These cold temperatures make the broccoli think it has gone through winter and is time to flower. 

Cucumbers and melons may also stop growing if the temperatures get too cold. Bring them in at night until temperatures stay above 50°F.

If your area is still experiencing cold temperatures, placing your seedlings in a low tunnel, cold frame, or hoop house can provide a buffer and help them slowly adapt to cooler temperatures. 

Transplanting Tips

  • Transplant on an overcast or cloudy day. 
  • Ensure your soil is loose, and add compost to the bed or planting hole.
  • Loosen the roots on any root-bound plants.
  • Water seedlings well.
  • Place mulch around seedlings.

It can be tempting to haul your plants out to the garden and put them in the ground on a sunny day. However, making the most of your plants requires a little more preparation. Hardening off your seedlings is essential to thriving crops. 

Basics: When to Start Seeds

A common question we get is, “I live [insert your state here}; when should I plant [insert variety here]?” As a small organization, we would need more time to answer all of these, and we’d like to enable folks to determine all their planting dates. Here’s what you need to do to determine when to start seeds, no matter where you live. 

Find Your Zone

Knowing your zone will help determine your first and last estimated frost dates and average winter lows. Armed with this information, you can make better choices about starting seeds and what varieties of annuals and perennials are best suited to your climate. 

Find your zone by using the USDA Plant Hardiness Zone Map.

Get Local Recommendations

If you can read this blog on a phone or computer, you can also access many personal planting charts available. Our gardener planner app provides planting dates based on your zip code. You can also find free planting dates by zip code on the Farmer’s Almanac website

If you like books, we also recommend grabbing a local gardening guide. These typically include much more than just planting dates and can provide other handy advice for dealing with your local climate, pest issues, and soil conditions. 

Most extension agencies also offer planting dates. In many cases you can get a planting calendar for your state, regions, or possibly even county from your local extension agency. They often have good advice for what varieties thrive in your area too. 

Pick Your Own offers a list of agencies if you need help finding yours. 

Brassica seedlingsStarting Indoors: The Basics

We recommend starting most of your seeds indoors 4 to 6 weeks before you expect to transplant them. This amount of time works well for tomatoes, sweet peppers, eggplants, collards, cabbages, broccoli, and other brassicas. Some crops like onions, hot peppers, celery, and celeriac are slower to get started, and you should start them indoors about 8-10 weeks before you want to transplant them.

Winter is tough on gardeners, and it can be tempting to begin sowing seeds indoors extra early. Unfortunately, giving the plants extra time indoors can be detrimental. If seedlings get too large, they can experience greater transplant shock and suffer damage.

Direct Sowing: The Basics

Direct sowing dates vary widely with crop type. Hardy, cool weather-loving crops like peas and spinach can be direct sown months before the heat-loving stars of summer like squash and watermelons. Some flowers are delicate and can only be direct sown after all chance of frost has passed, while some can be direct sown in the fall to overwinter and get an early spring start. 

Read about your chosen varieties and look at your area’s estimated last frost date. For future years, keeping a garden journal about what you planted, when, and how it faired can be helpful.

Knowing when to start seeds doesn’t need to be guesswork. You can use these resources to start seeds at appropriate times and grow a bountiful garden. 

8 Common Mistakes When Starting Seeds

Starting seeds indoors is one of the best parts of gardening. You can finally get your hands in the soil after a winter break. A gardener’s shelf full of tiny seedlings is a sure sign that’s spring is on its way! Unfortunately as with everything in gardening growing transplants from seeds has its challenges. If you want to have awesome seedlings this year be sure to avoid these common mistakes.

Not providing supplemental light.

Unfortunately, setting your seedlings by a window probably isn’t going to give them enough light to become strong and healthy seedlings. Odds are they’ll become tall and spindly, reaching towards the light. You’ll have to provide them with some form of supplemental light. You don’t need to buy actual grow lights, simple garage or shop lights will do. You want the lights to be as close as possible to the tops of the plants without burning them. Setting up your lights so you can easily adjust their height as the plants grow is a great idea.

Not addressing a variety’s specific needs.

While many seeds are pretty simple to grow, just push it some dirt and water, others require a bit more care. Some seeds need to be soaked overnight before planting, some need light to germinate, while still others need to scarified. Always check package directions and do research as needed. 

Not hardening off your seedlings.

As your seedlings are accustomed to a climate controlled life indoors, they could succumb to shock if you decide to set them out without first acclimating them to their new environment. Start by setting them outside for just a few hours per day slowly adding time over the course of two weeks. This will allow them to adjust the intense sunlight, temperature, and wind. You can take this a step further by transplanting your seedlings on an overcast day so they don’t have to struggle with intense light on top of the shock of transplant.

Over or under-watering.

Seedlings should always be kept moist but they’ll rot if they’re just sitting in water. Whatever you plant your seedlings in should a hole or holes in the bottom and a tray underneath to catch any excess water. You also need to ensure that they don’t dry out completely which can happen surprisingly quickly as seedlings grow larger.

Not putting them somewhere noticeable.

Unless you’re a full-time market gardener it’s easy to forget about and neglect your seedlings. Setting up your shelf somewhere you walk by often will help you remember to care for them and make it easy for you to spot problems as soon as they arise. 

Not keeping them warm enough.

While some plants like spinach and lettuce germinate and grow well in cool weather, others like tomatoes and peppers like things pretty warm. If you notice that your seeds are taking a long time to germinate, are slow growing, or you live in a cool or drafty home you may want to invest in a heat mat. These can be placed underneath seedling trays and will help the soil stay at an optimum temperature. 

Using garden soil instead of a proper potting medium.

You don’t necessarily have to buy a potting mix but you do need something other than plain old garden soil. Potting mixes always include something like peat moss to hold some moisture but are also light so that they drain well. You can find many DIY recipes for potting soil on the internet. If you’re purchasing soil and want it to be organic look for something that’s OMRI (Organic Materials Review Institute) certified.

Starting them too early and/or not potting them up.

If you start your plants too early they can outgrow your pots before your ready to plant them out. In this case, you’ll need to pot them up. If you don’t do this they can become root bound which may stunt their growth and weaken them.  

If you’ve struggled with growing your own transplants in the past being careful to avoid these common mistakes can help you have a productive garden this year. 

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