Whether you purchased young plants at a garden center or started them yourself from seed, eventually, they'll need to be transplanted. 

Don't take them straight from the house and stick them in the ground. There are a few steps to ensure a successful transition for a beautiful garden and a bountiful harvest.

When is the Right Time to Transplant?

For many of us, transplanting time is mostly driven by environmental conditions. Frost dates are the most obvious driver of timing. Plant your young tomato plants out before your last frost, and you'll likely get to buy more tomatoes. It's a painful lesson. However, there are other factors to consider as well.

Weather Conditions

Knowing your last spring frost date–for gardeners who receive freezing weather–is a vital bit of information. Average last frost dates are quite localized based on topography, distance from large bodies of water, and local weather patterns. Your last frost date may occur a week or two before or after that of a location half an hour away. 

While your average last frost date is important, it isn't foolproof. Those dates are averages, and your actual last frost will vary. Watch the long-range forecast and the predicted overnight lows. You may be able to sneak your plants in a week or two early or decide to wait another week while some cold weather passes. 

Cool weather crops like brassicas (broccoli, cauliflower, cabbage and more) can withstand light frosts. You'll be okay planting them out a couple weeks before your last frost date. Warm weather crops like peppers and tomatoes will not tolerate any freezing temperatures, and need to have warmer temperatures. 

Weather influences soil temperatures as well. Cool-season crops don't mind soil temperatures in the forties and fifties, but most garden vegetables and many annual flowers don't like them. 

Seedling Age and Size

It's pretty easy to see when a plant has become too large for its current pot and needs transplanting. Rootbound seedlings with masses of circling roots or stunted growth obviously need a new, larger home. However, seedlings can also be transplanted too early. 

Generally, you'll want seedlings to have at least two pairs of true leaves before transplanting outside. The first leaves to appear when a seed germinates are called cotyledons or seed leaves and typically don't resemble normal leaves of the plant. For example, new cucumber leaves are thick, fat, and oval-shaped–not at all what mature cucumber leaves look like.

Leaves that appear after the cotyledons will be true leaves. They’ll have the same shape and structure as mature leaves for the plant. 

The Process of Transplanting Seedlings

The weather looks good, the seedlings are ready, and you've found your gardening gloves. But the process of transplanting starts a few days before dirty-knee day. 

Hardening Off

Letting young plants become accustomed to outdoor environmental conditions is probably the second-most important step in transplanting after paying attention to your frost date.

Most plant starts are grown in a greenhouse or grown in your home. If they didn't need protection from the elements as young plants, we would have grown them outside from the start! Seedlings need a week to ten days of gradual exposure to their new outdoor environment before being tossed out to make it on their own.

We have an entire article on hardening off seedlings, but here's the quick version.

1. Start a week or two before you want to transplant. 
2. Choose a protected location safe from small critters, high winds, or bright sunlight.
3. Begin with gentle sunshine. For the first few days, expose seedlings to morning light or dappled sun for only a few hours at a time. Avoid hot, harsh afternoon sun or giving them too much at once.
4. Introduce a breeze gradually. A windy day isn't the ideal time for setting out new seedlings. Use sheltered areas and let them get used to swaying in the wind over time.
5. Reduce watering frequency. Your seedlings have been pampered, but they need to expand their root capacity and get used to a less regular watering schedule. 
6. After a week, your seedlings can remain outdoors all day and be brought in at night if the weather turns cold. 

Think of it like starting a workout program. It's wiser to begin gradually instead of jumping in whole hog with max effort on day one, overstressing yourself so you're too sore to move on days two and three. Work seedlings up to outdoor conditions gradually.

Soil and Garden Bed Prep

While your seedlings are hardening off, you can prepare their new homes. 

• Remove any weeds and loosen the soil with a garden fork or broadfork. This is also a good time to work in an inch-thick layer of compost. 
• Pick out those last few rocks that appeared out of nowhere, and get your mulch supplies ready to hand.
• Rake the surface smooth; if the soil is dry, water it the day before planting. 

Transplant Day

It's finally here! Transplant Day is exciting. Your garden will go from looking like bare soil to being worthy of photographs. Pretty green plants will be in their new homes, and evening garden tours can begin. Here are a few tips to help transplant day go smoothly.

Watering Before Transplanting

• Give your young plants a final drink in their old containers a few hours before transplanting. The plants will take up water, reducing stress when their roots are disturbed.
• Moist soil releases from the container more easily, allowing the plants to slide free. 

Removing plants from their pots

• Seedlings may be in soil blocks, flats, cell trays, or individual containers. Regardless, they'll need to be separated. If you have more than a few, laying them in their proper spacing as you separate them can make it easy to see if you need to adjust or find more room.
• For young plants in plastic containers, gently squeeze the sides of the pot, then release and tip the plant and container on its side. The plant should slide out without too much resistance. If roots are sticking out the drainage holes, you may need to trim them to avoid further damage. Gently tease the plant from the container and set it near its new home.
• Seedlings in flats can be teased apart, taking care to avoid ripping off roots. Soil blocks are easy to separate with your fingers. 
• If a young plant has become rootbound, rough up the edge of the rootball with your fingers or use a sharp edge to score the rootball in several places. Any circling roots should be cut, as they can later girdle the plant.

Stick 'em in the ground!

• Depending on the size of the hole needed, use your fingers, a dibble, or a garden trowel. For containerized stock, the hole needs only be slightly larger than the rootball if your garden soil is already loose.
• Take care to use proper spacing for mature plants. They’ll look like they’re a long way apart, but the space will fill in as they grow.
• Set the plant in the hole and test the depth. 
• For most plants, keep the seedling at the same depth (or a hair deeper) than it was in the pot.
• For tomatoes, bury them deeper, up to just below the first leaves. Roots will form along the buried portions of the stem. 
• Gently firm the soil around the roots to ensure no air pockets remain.
• Water gently with a watering can or wand on a hose around the base of the plant. Give them a nice, long drink. This will settle soil around the roots and provide a store of moisture for a few days.

After Transplant Care

Watering

Newly transplanted plants will need more frequent watering than well-established gardens. Despite careful handling, some root damage is nearly inevitable, and nearby dry soil can steal water from around their roots. 

Check the soil moisture near your new transplants daily, and water as necessary to keep the soil slightly moist an inch deep. Your finger makes an excellent soil moisture probe, and you'll soon get a feel for it.

Weeding

Little plants need protection from competition. Just as our seeds germinate in spring, so too do weeds. Spring is usually the most frustrating time for weeding, and letting the weeds get a foothold can not only slow your plants' growth but also make it hard to distinguish friend from foe. 

Weeds will grow faster than your plants and can entwine their roots with those of your young seedlings. Take care when weeding either by hand or with a tool to avoid damaging the roots of your new plants. Some weeds are better off snipped if they are too close to the stem of your tomato or pepper. 

Make a habit of doing some weeding a day during the spring, and you'll never have to face the arduous day-long chore of trying to catch up.

Mulching

Bare soil between plants dries out quickly and invites many more weeds than I want to deal with. Mulch keeps the soil moist, prevents a hard crust from forming, encourages beneficial soil microbial life, and eventually turns into soil organic matter. It really is the key to easy gardening. 

Use a thin layer when seedlings are new, and keep it from touching the stems. Apply a thicker layer as they grow, keeping ahead of the weeds. 

Transplanting Pro Tips

• Label varieties with stakes in the garden, on a garden map, or in your journal. You'll be able to track which ones performed well and which didn't. 
• Don't worry too much about a dropped leaf. Seedlings can naturally look cranky and stressed for a few days after transplanting. Keep them adequately watered (not too much) and watch the cold snaps, and they'll be fine.
• Pay close attention to the weather. I’ve often transplanted only to spend a near-sleepless night worrying about an unforeseen turn of the weather. Keep some frost cloth handy and a few rocks or weights to hold it down. It’s inexpensive, and it can save your crop.