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204-Hardening Off and Setting Plants Up for Success in Spring

| Podcast, Prepare

We’re all anxious to get our plants in the ground, but if we’re not careful and we rush it, we can really set our plants’ progress back significantly. It’s an exciting time in the garden, but also a time to exercise restraint and self-discipline. On this week’s podcast, I share tips for setting plants up for success in spring, starting off with the art and science of hardening off. 

You may have heard a lot of this advice before, especially if you are an avid listener of the podcast, but in your gardening life it never hurts to go back and review these essential fundamentals. When we skip over the basics — like forgetting to harden off seedlings before transplanting them outdoors — those plants that we put so much effort into starting from seed can falter. And there is nothing more disappointing than fumbling the ball at the five-yard line. 

Before proceeding with my tips to set plants for success, a quick reminder that you can sign up to be notified when enrollment opens for my upcoming Online Gardening Academy™ course, Growing Epic Tomatoes, co-led by Craig LeHoullier. This brand new course will turn you into a tomato-growing expert in no time.

 

Why Harden Off Seedlings

Hardening off seedlings is a process of readying tender young plants to live outside. It could be that you started the seedlings indoors yourself or you purchased them. Either way, the plants need to be slowly introduced to the outdoor environment to prevent shock that could set back their growth. Even greenhouse-grown seedlings can become sunburned once outdoors if the greenhouse has any opacity at all.

Seedlings that were raised by a sunny window or under grow lights are accustomed to only a fraction of the amount of light that the sun can provide. In fact, even a high-end grow light is only a tenth as effective as the sun is at providing usable light for photosynthesis. 

Imagine the shock it would be if you went from being inside 24/7 with just 10 percent of the light that the sun puts out, to being outside, with no sunscreen, in direct sunlight all day. The sun would do a number on you — and the sun can do the same to plants.

Plants must be eased into that environment, or they will get burned. The leaves will appear pale or tanned, the foliage will become bleached and the plants will begin to shrivel up. Fortunately, any new leaves won’t be affected, because they grew from the start in outdoor conditions, but those old leaves may drop off.

If you have never hardened off plants before, it’s hard to gauge the progress. But the first time you see sun-burned leaves, you’ll know it, and you’ll never forget it. 

Sudden exposure to full sun typically doesn’t kill plants, but it can set back their growth by several weeks as they recover. Though it takes patience to harden off plants effectively, your plants will be much better off for it and you’ll be much happier with the results. 

 

Damaged tomato seedlings

The pale, bleached leaves on these seedlings are a direct result of being left out in the sun too long.

 

How to Harden Off Seedlings

The process of hardening off starts with bringing seedlings outdoors for just a half-hour, and then returning them indoors. This can feel like a lot of work for such a short amount of time, but any longer than 30 minutes in direct sunlight is not recommended. The sun can severely impact plants that first day, so it’s not worth the risk of leaving them out for a prolonged period.

On day two, increase the time outdoors to an hour. On days three and four, add 30 minutes or so each day. By day five, start bumping up the duration by a full hour each day. That way, at the end of a week or 10 days, the seedlings will be ready to spend a full day outdoors and can then be transplanted into the garden.

 

Tomato seedlings enjoying sunshine

These are just some of the 3,350 plants my daughter Amy and I started from seed this year for our annual spring plant sale. These tomato seedlings were enjoying a brief exposure to sunshine.

 

Another Way to Harden Off Seedlings

Not everyone’s schedule allows them to move plants twice a day during daylight hours — they may be working or have other responsibilities — and that’s OK. There is an alternative way to harden off seedlings.

I have more than 3,000 seedlings that need to be hardened off each spring, so once I move them outside, they stay outside (unless there is frost in the forecast). To protect them and harden them off, I use shade cloth. I start with a shade cloth graded for 70 percent UV protection, which gets the level of light closer to what the plants were used to under grow lights. In my experience, they show no signs of burning.

After a few days under a 70 percent shade cloth, I’ll switch to a 60 percent shade cloth, then 50 percent, then 40 percent. But it’s not necessary to go by 10 percent increments — you can start with 70 and go down to 50 and then 30, as long as it’s gradual. Either way, you have to keep a close eye on the plants for any signs of burn and be ready to react.

If a late frost warning forces you to bring the plants indoors, turn the hardening off clock back a couple of days when you bring them back outdoors.

If you don’t have shade cloths, you can find dappled shade under a tree canopy, follow the shade cast by your house, or avoid putting seedlings outdoors during the middle of the day and the afternoon. Any of these tricks will reduce plants’ exposure to the full intensity of the sun.

 

Shade cloth over seedling trays

One way to effectively harden off seedlings is to cover them with shade cloth to add protection from the harsh sun.

 

More Reasons to Harden Off Seedlings

Sun exposure is just one of the reasons to harden off seedlings. The two other primary reasons are temperature and wind.

Exposure to cold wind is never good for tender seedlings — cold wind is drying, and the desiccating effect can be brutal for plants. Hardening off will help acclimate the plants for what’s ahead.

Plants will surprise you with how resilient they are in low temperatures, but the closer to freezing that the temperature dips, the more dangerous it is for plants, certainly for those with no frost tolerance, like tomatoes and peppers. 

You can avoid the coldest wind and chilliest days by waiting to start the hardening off process until closer to the last expected frost date.

Improve the Growing Conditions for Your Plants

If you are finding reduced performance from your garden, it may or may not be the soil. Look up first — the problem could very well be overhead.

Your plants need sunlight to be happy, so be mindful of trees and structures that cast shadows over your garden. It could be that your garden had all the light plants required when it was first established, but then trees grew in over the years and began to filter or block the light. And this may not even be apparent until later in the season, once the trees have put leaves on.  It could be time to limb up the trees or remove some branches to reclaim those hours of direct sunlight.

Don’t Rule Out a Garden

A lack of space doesn’t mean you can’t start or expand an edible garden. Edibles can be planted among the ornamental landscape — this is called foodscaping — or planted in straw bales and grow bags that take up minimal space. Container gardens can even be placed on rolling platforms to chase the sun. 

 

A tomato seedling in a straw bale

Straw bales are a way to expand your garden, and they take up minimal space.

 

Deposit Nutrients in the Bank

I apply compost to my garden twice a year, once heading into spring planting and then again at the end of summer for my fall garden. A 1-inch layer of compost scratched into the surface of garden beds, or simply topdressed, will replenish the nutrients in the soil for greater fertility and improve the soil’s microbiology — the soil food web.  

I like to think about garden nutrients as a bank account. If you only make withdrawals and never make a deposit, soon your bank account will be empty. Well, the nutrients that plants take out of the soil as they grow are the withdrawals, and applications of compost,  vermicompost worm castings and slow-release fertilizer are your deposits. Continue to make steady deposits, and you will have healthier, more productive plants.

 

adding TerraThrive worm castings to planting holes for successful spring plants

I like to add vermicompost worm castings when planting to help increase my soil’s fertility and add nutrients back to the soil.

 

Get a Soil Test

Your local county extension service offers soil tests for a low cost that will tell you what nutrients are deficient — or abundant — in your soil, and will let you know the soil’s pH, which is a scale of how acidic or alkaline the soil is. When the pH is out of balance one way or the other, many nutrients that are already existing in the soil will become chemically bound. Bringing the pH closer to the middle — 7.0 — will make those nutrients more readily available to plants.

Just as important as learning what you need to add to soil to make it more productive is learning what you don’t need to add. If you apply fertilizer or a soil amendment that is not needed, it can be, at best, a waste of money and effort, and at worst, detrimental. Too much fertilizer can burn plants or destroy beneficial microbes in soil.

A county extension service typically charges $15 or $20 for a soil test, and the results come back in about 10 days with valuable information. These days, there are also many private labs found online that will test soil for around $30 and provide a PDF of results with even greater detail than a typical county extension test. Some private labs are also better than many county extensions when it comes to providing organic solutions in addition to non-organic, synthetic recommendations. 

Some labs can test for certain diseases or certain metals in soil. If you have those concerns, it’s worth spending the few extra dollars to order those soil test add-ons from a reputable lab. 

 

Collecting soil for a soil test

Getting a soil test can help you determine now what nutrients are deficient in your soil so you’ll know what amendments to make.

 

Give Plants Space

Going overboard is a problem among new gardeners especially, but even experienced gardeners can be guilty of packing in plants too densely.

When we plant seeds or seedlings, they are relatively small, and the instinct is to plant them closely together. It’s hard to imagine just how massive those plants are going to become from such a small seed. The problem with dense planting is it reduces sunlight to plants and the air circulation between them. The more dense the plants are, the more likely they are to succumb to pests and disease. 

We want our plants to be healthy and our gardens to be productive and rewarding. Keep that in mind at planting time, space out the plants to meet their needs, and avoid frustration later. Seed packets or plant tags should include spacing requirements, but if you don’t have that information, an online search can answer your questions.

 

Spacing seedlings with a planting board

Properly spacing plants out during planting time can help prevent them from having pest and disease issues later.

 

Ensure Proper Drainage

You’ve probably heard me say this before: More plants die from overwatering than underwatering. When soil is not well draining, and then we apply water or a big rain comes, water displaces the air in soil that the roots need to breathe. As the water sits there around the roots, the plant can literally drown. 

Adding organic matter to soil will improve drainage, whether the soil is slow-draining or fast-draining. Organic matter such as compost retains some water while shedding excess water, so roots don’t dry out between waterings or drown in too much water.

Grow bags, other containers, and raised bed gardens with improved soil are quicker to drain than in-ground gardens, and each can be a solution to overcome water-logged soil. 

 

Tomato plant in a grow bag

Grow bags and other containers are quicker to drain than planting in-ground and can be a great solution to deal with waterlogged soil.

 

Avoid Overhead Watering

I really enjoy hand-watering the garden. It allows me to keep a close eye on the plants and watch out for pests and diseases before they get out of control — that’s why a gardener’s shadow is the best thing for a garden. But what I don’t do is overhead watering.

 

watering plants

Avoid wetting the leaves when hand watering by applying water at the base of the plant.

 

Overhead watering means sprinkling water right onto plant foliage. Watering this way, especially late in the day, allows moisture to sit on the leaves and fruit of plants, and that creates an ideal environment for many plant pathogens to flourish. Instead, apply water right around the root base, under the foliage. A soaker hose or a drip irrigation system is another way to accomplish this.

The slower water is applied, the more effectively roots can take it up. When water is applied quickly, much of the water runs off, which is not only wasteful, it reaches surrounding weeds and helps those weeds grow.

 

Irrigation in raised beds

Drip irrigation is one way to avoid overhead watering.

 

Add a Layer of Natural Mulch

Organic mulch protects the soil surface from erosion or compaction, creates a barrier between plants and soil-borne disease, suppresses weeds, retains moisture between waterings, and breaks down in time to improve the soil. 

I collect leaves all fall to shred and then apply as mulch in spring for a healthier garden the whole growing season. Other popular organic mulch options include wood chips, straw, bark, and pine needles.

 

raised beds with leaf mulch

Adding a layer of natural mulch like fall leaves provides numerous benefits and can result in a healthier garden the whole season.

 

Document Your Garden Journey

Taking notes and pictures in the garden is a great habit to get into. It’s better to have and not need the information than to need and not have it. Take my word, at some point you’ll be glad you have the info. Your notes will help you notice trends, changes and anomalies. 

I use an app on my phone called Day One, which stores information on the cloud forever and updates it across all your platforms. Day One is basically a journaling app, and it offers dictation. What you say will be transcribed into a searchable, downloadable note.

If you observe something in the garden and don’t make note of it right away, you are likely to forget it, or at least forget when you first noticed it. That’s why I do all my note-taking in the garden before I move on.

 

DayOne journal

I use the Day One app on my phone to keep track of observations I make in my garden throughout the season.

 

I hope you found these tips on setting up plants for success in spring helpful. If you haven’t already, you can listen to this episode now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title. 

What steps do you take to set plants up for success in spring? Let us know in the comments below.

Links & Resources

Some product links in this guide are affiliate links. See full disclosure below.

Episode 040: Prepping Your Garden for Spring: 10 Things to Do Now

Episode 079: Foodscaping: How to Create an Edible Landscape, With Brie Arthur

Episode 097: Spring Tips for Vegetable Garden Success

Episode 124: Using Compost the Charles Dowding Way: More Than Just a Great Soil Amendment

joegardener Blog: How to Improve Your Soil: 3 Simple Steps for Making Any Soil Better

joegardenerTV YouTube: How to Take a Soil Test

joegardenerTV YouTube: The Basics of Soil pH

joegardenerTV YouTube: How to Add Compost in the Garden

joegardenerTV YouTube: Edible Landscaping – How to Create a Foodscape

joegardenerTV YouTube: Building Soil for Raised Bed Gardens – The Perfect Soil Recipe

joegardenerTV YouTube: Drip Irrigation Kit Basics

joegardener Online Gardening Academy™: Three popular courses on gardening fundamentals; managing pests, diseases & weeds; and seed starting.

joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.

joegardener Online Gardening Academy Growing Epic Tomatoes: Tomato expert Craig LeHoullier joins me in leading this course on how to grow healthier, productive tomato plants and how to overcome tomato-growing challenges. You can sign up to be notified when enrollment opens.

joegardenerTV YouTube

joegardener Newsletter

joegardener Facebook

joegardener Facebook Group

joegardener Instagram

joegardener Pinterest

joegardener Twitter

Growing a Greener World® 

GGWTV YouTube

Shade cloth 

Day One app

TerraThrive™ – Our podcast episode sponsor and Brand Partner of joegardener.com 

Territorial Seed Company – Our podcast episode sponsor and Brand Partner of joegardener.com – Enter code JOEGARDENER for 10% off your order

Greenhouse Megastore – Our podcast episode sponsor and Brand Partner of joegardener.com – Enter code JOEGARDENER for 10% off your order

Disclosure: Some product links in this guide are affiliate links, which means we would get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us. None of the items included in this list have any bearing on any compensation being an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, Milorganite, Soil3, Exmark, Greenhouse Megastore, High Mowing Organic Seeds, Territorial Seed Company, Wild Alaskan Seafood Box and TerraThrive. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.

About Joe Lamp'l

Joe Lamp’l is the creator and “joe” behind joe gardener®. His lifetime passion and devotion to all things horticulture has led him to a long-time career as one of the country’s most recognized and trusted personalities in organic gardening and sustainability. That is most evident in his role as host and creator of Emmy Award-winning Growing a Greener World®, a national green-living lifestyle series on PBS currently broadcasting in its tenth season. When he’s not working in his large, raised bed vegetable garden, he’s likely planting or digging something up, or spending time with his family on their organic farm just north of Atlanta, GA.

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