A Summer-Long Punch of Color: Growing Annuals in the Garden

A bed of mixed annuals including tender perennials, summer bulbs, seed grown flowers and colorful grasses.

A bed of mixed annuals including tender perennials, summer bulbs, seed grown flowers and colorful grasses.

Annuals have certainly come a long way since the humble red geraniums and simple zinnias of the past.  These days, nurseries are overflowing with mounds of colorful and exotic flowers of every size and shape.

So whether you’re looking to create a lavish window box, add a little curb appeal to your front walk, or  just fill in a few gaps between your shrubs and perennials, an infusion of annuals may be just what your garden needs to get it from now to wow!

Technically, “annuals” are plants which complete their life cycles (grow, flower, set seed, and die) within one year or growing season. They include flowers, vegetables, herbs, ground covers, and vines. Plants labeled “tender perennials” are best treated as annuals in our hardiness zone, as they will likely not survive our winters and, therefore, will not return the next year as true perennials will.

Window boxes are great for showcasing annuals. Make sure they have holes for drainage and are big enough to accommodate your plants as they grow. Because window boxes dry out quickly, they will need frequent watering. To keep soil and water from spilling out when watering, don’t fill boxes all the way up to the top with soil. Instead, leave at least half an inch of space between the soil line and the rim of the container. This allows water to puddle and slowly soak in, which not only keeps siding from being splashed with mud, but also provides plants with deeper, more effective watering.

Designing Annual Flowerbeds

Sectioning large annual beds into grids can ensure adequate spacing between plants and make it easier for designs drawn on paper come to life.

Annual flowerbeds can be created by laying garden hose or twine on the ground until the appropriate shape is obtained. Use this marker as the pattern to edge out the bed.  Bed lines can be straight or rounded, but curved lines are always more visually interesting.

Planning the design on paper with the correct spacing for a given plant will help assure that you have the right number of plants for your design. Keep taller annuals to the back of the border, and dwarfs and low annuals to the front.

In established beds, sectioning off planting grids can aid in plant placement, making sure that overall spacing is even and each variety has enough room to grow.

The sky’s the limit when it comes to color selection. There are so many vibrant primary and soft pastel colors available that endless combinations are possible.  Don’t only consider flower color when it comes to annuals. Lots of annuals offer interesting foliage or interesting seed heads, even veggies can add a fun, unexpected element.

When it comes to annuals, don’t limit your thinking to flowers alone, vegetables –like these ornamental peppers– make great additions to gardens and containers.

How to Plant Annuals

SITE SELECTION: Different plants have different requirements for sun, shade, soil quality, and drainage. Most annuals prefer full sun, rich garden soil, and good drainage.

One of the best things about annuals is their incredible diversity in color, form and texture– providing exciting combinations that last all summer.

Other factors to consider when choosing where to plant your annuals are visibility, (i.e. will you be able to see and enjoy them where they are planted?) and accessibility for maintenance (will you be able to get to them to remove dead flowers, to weed, and to fertilize?)  The average flower border should be no wider than 5 to 6 feet, so the middle can be accessed from both sides without stepping into the garden.

SOIL PREPARATION: Most annuals need soil that is loose enough for the roots to grow easily. Adding organic matter to heavy (clay) soil will help loosen it. Organic matter also can be added to sandy soil. For the average garden bed, add 1 inch of compost, peat moss, or well-rotted manure to the garden.

Have a soil test run to determine the pH or relative acidity. If lime is needed to raise the pH of an acid soil, apply according to soil test recommendations or use 3 to 5 lbs. of lime for each 100 sq. ft.

FERTILIZER: Annuals grow quickly and need fertilizer to nourish that growth. Use a complete fertilizer, either chemical or organic, such as 10-10-10, 5-10-10, or 5-10-5 applied at the rate of 2 lbs. per 100 sq. ft. and rake or spade into the soil before planting. Side dress at mid-season as required by individual plants. Plants may be sprayed with liquid seaweed, fish emulsion, manure or compost tea several times during the season.

PLANTING – SEED: Follow seed packet instructions for distance apart and correct depth of planting. Timing of planting is also important, because some seeds are not frost or cold tolerant and must be sown when the soil is warm. Cover the seeds with fine soil and water thoroughly.

If you raise your own plants from seed make sure they are “hardened off” for a week before transplanting. Tender plants usually sunburn or die if not hardened off by stopping fertilizer applications, lowering temperature, and increased ventilation. Gradually expose them to outdoor conditions before the transplant date.

Select short, stocky plants with dark green foliage. Avoid tall, spindly plants. Small to medium-sized transplants become established in the garden more quickly than large ones.

PLANTING – TRANSPLANTS: Select healthy, robust seedlings in individual pots or 6-8 packs from your garden center. Reject any plants that appear stressed or infested with diseases or insects.

Purchase as close to planting day as possible, but be sure that plants that can’t tolerate frost aren’t planted too soon. Our frost-free date (central New Jersey) is usually near May 10. Each year varies. Don’t be so eager to get an early start that your plants will be damaged or killed by late frosts. Be prepared to cover those that may be threatened.

On an overcast day, planting can be done anytime. On a sunny day, transplant the seedlings in early morning or late afternoon so midday sun doesn’t damage them.

After removing the plants from their container, check the root system. If the roots are tightly massed and take the form or the pot, they must be cut slightly or loosened a little so they will be able to grow into the surrounding soil.

Set the plants in the ground at the same depth they were in the pot and settle soil around them gently, being sure not to leave any air pockets around the roots.

Water thoroughly. Some gardeners use a transplant solution of water-soluble fertilizer, compost tea, or liquid seaweed mixed according to the label to reduce transplant shock.

Form and Flower:  A pleasing combination of alyssum and plectranthus blends the white margins of the Plectranthus with the tiny white flowers of Alyssum. The textural contrast between the two plants makes this pairing particularly charming . (Photo by Kathy Enquist)

How to Care for Annuals

WATERING: All plants need water to grow. For most annuals, watering at the rate of one inch of water per week will be enough. Use a rain gauge to determine how much rain has fallen, and reduce watering accordingly. Some plants, such as California poppy, are content with less water. When irrigating, water thoroughly, preferably in the morning. Frequent, shallow sprinkling encourages shallow root systems and disease development.

MULCHING: Using organic mulches, such as grass clippings or shredded hardwood, or inorganic mulches, such as black plastic or polyethylene weed barrier, helps to maintain even soil moisture and temperature and  deters weeds. Be sure to use a little extra fertilizer (complete analysis, such as 10-6-4 or 10-10-10) when using woodchip mulches to offset the nitrogen used up in the decomposition process. Sometimes, organic mulches harbor pests such as earwigs and slugs, but this disadvantage is usually offset by the advantages of mulching.

PINCHING AND SHEARING: Some annuals, such as sweet alyssum and lobelia, benefit from pinching their tips to encourage branching or to maintain form.

Zinnia are among the annuals that benefit from deadheading, which will help the plants remain attractive, keep them from going to seed, and increase flower production.

DEADHEADING: Removal of spent flowers to keep plants productive and to maintain an attractive appearance is called “deadheading”. Marigolds, zinnias, calendula, and others benefit from this form of pruning. Do not deadhead from early September on if seed dispersal is desired for self-sowing or if seed is going to be harvested.

SIDE-DRESSING: Annuals grow rapidly in order to complete their life cycle in one growing season. In late June or early July, applying a second application of fertilizer near, but not on, the plants, gives them a boost. Follow label directions for how much to use.

STAKING: Taller annuals, such as snapdragons and African marigolds, benefit from added support so heavy rain and wind don’t knock them over. Tomato cages, bamboo and metal stakes, are among the forms of support that can be used to keep plants upright.

Annual sunflowers are a great addition to beds and borders. Their big, daisy-like flowers come in a variety of colors and sizes–some that tower over 16 feet in height, while others are better suited for smaller spaces and containers.

PEST CONTROL: Pests take many forms: weeds; insects; fungal, viral, and bacterial diseases; mites; mollusks (slugs); and animals. Luckily, pests don’t usually bother most annuals. Take care to keep weeds out of the flowerbed to avoid competition for available nutrients and water, especially while plants are small.

Most pest problems can be solved or controlled without the use of toxic chemicals.  Before reaching for pesticide sprays , consider one of the many cultural, biological, or mechanical means at your disposal. Chemical attack should only be used as a last resort when other methods fail.  The best defense against garden pests is keeping plants strong  healthy, and protected by natural enemies.  Consider the following for creating good growing conditions for your plants and unfavorable conditions for pests:

  • When buying annuals, look for disease-resistant varieties.
  • Be careful not to under or over- watering–both make plants vulnerable to insects and diseases.
  • Change the location of your annuals  from year to year–this helps to disrupt the life cycle of pests.
  • Plant a variety of plant species — which will lessen overall damage should a pest gain a foothold and also provide welcome habitat for beneficial insects that can keep garden pests in check.

If pest problems still arise, we’re here to help! Consult with a Master Gardener from Rutgers Cooperative Extension by calling our Garden Helpline at (609) 989-6853.

Need a Little Annual Inspiration?

Looking for some ideas for adding annuals to your own garden? Visit the Annual Garden at the Mercer Educational Gardens in Pennington.  Each year Mercer County Master Gardeners select a new slate of annuals to grow from seeds and plugs.  So come out and visit us –you may walk away with some fresh ideas for plants and combinations you might not have thought of before…

A glimpse of the annual garden at Mercer Educational Gardens in Pennington, NJ. Each year Rutgers Master Gardeners of Mercer County set out to create new color combinations and textures to bring to life two large garden beds composed entirely of annuals.

More information:

ANNUAL PLANTS FOR THE GARDEN, Barbara J. Bromley, Mercer County Horticulturist

ANNUALS FOR DIFFICULT SITES Barbara J. Bromley, Mercer Co. Horticulturist 2015

ANNUALS FOR HEAT AND DROUGHT, Barbara J. Bromley, Mercer County Horticulturist

PLANTING HIGH VISIBILITY FLOWER BEDS Barbara J. Bromley, Mercer Co. Horticulturist

BASICS of FLOWER GARDENING Barbara J. Bromley, Mercer County Horticulturist


Ready, Set, Plant! Tips for getting your garden off to a great start

Stacks of lush spring plants are hard for just about any gardener to resist!  Before buying, don’t forget to read plant labels and make sure conditions in your garden and the plant’s cultural requirements are a match. (Photo by Joe Scarlata)

Plant sales abound this time of year and whether you’ve been shopping at neighborhood  plant swaps or browsing through local nurseries — you know how energizing the experience can be. But once you arrive home,  do you ever find yourself saying, “Now what?”  If so, we’ve got you covered!  We love plants sales too, so we’ve put together a few Master Gardener “Tips of the Trade” that will have you digging in to this– the most optimistic of garden seasons–with excitement and confidence.

It’s planting time!  The frost free date in central New Jersey is on or after May 10 –so now’s the time for gardeners to get growing.

Ready or not: What to do if planting’s on pause…

If you’re NOT planning to transplant your new plants immediately,  remember to water them as needed and protect them from animals and harsh elements such as frost and wind until you are ready to plant them.

For the best results for all of your garden plants–as well as your lawn–you should know the pH and nutrient level of your soil.  To do this, have a soil test run.  You can stop by the Extension Office to purchase a soil mailer, or call the Extension Office at 609‑989-6830 for more information.

Planting  101: Steps to help your new plants thrive

The following tips apply to most newly-purchased plants.  But, be sure to check plant labels first for any variety-specific instructions.

SITE CONSIDERATIONS: Read plant labels carefully before selecting planting sites. Plants have different requirements for sun/shade, soil condition and drainage.

Individual annuals and perennials have different requirements for sun, shade, partial sun, soil quality, and drainage. When deciding what plant to put where, also consider a plant’s mature height and whether you will you be able to see and enjoy it among its garden companions. (Photo by Joe Scarlata)

Also, since plants have different growth patterns and rates of growth, consider the spread and the height of the plant at maturity.

In addition, two other factors should be considered:  visibility (planting in order for the plant to be seen and enjoyed) and accessibility (planting in order to for the plant be accessible for fertilizing, dead heading and/or pruning).

Make sure to remove weeds and debris before planting. It’s also a good idea to add some organic matter–like compost –into the soil to help new transplants thrive.  (Photo by Theodora Wang)

SOIL PREPARATION: Remove all weeds and other debris from the planting site.  Loosen soil for good root growth and mix in organic matter (compost, well rotted manure or peat moss) to amend the soil. If a recent soil test was performed, refer to the report for information regarding recommended lime and fertilizer. If no soil test has been done, fertilize with 10-10-10 at 2 lb. per 100 square feet, or follow the label directions on a fertilizer for flower or herb gardens. Spade or rototill amendments to a depth of 6-8 inches for most annuals or perennials.

The best time to install your plants is on a cloudy day, which reduces the chance of sun and/or heat stress on new transplants. (Photo by Joe Scarlata)

PLANTING: Hardy perennials, trees and shrubs can be planted immediately. (The frost-free day in central New Jersey is on or about May 10.) If tender plants– aka annuals– are threatened by frost, be prepared to cover them.

Plant at any time on a cloudy day, or early morning or late afternoon on a sunny day.  Prepare a space at least twice the size of the plant container and almost as deep. Remove the plant from the container and loosen or cut the roots slightly to encourage growth. Plant at the same depth as the plant was in the container. Gently settle soil around the roots, being careful not to leave air pockets around the roots.  Water thoroughly.

MAINTENANCE: Water early in the morning (preferable) as plant species require. Use a rain gauge to determine how much rain had fallen and adjust watering schedule accordingly.  Mulch will help maintain soil moisture, temperature and deter weeds. Mulch depth should never exceed two inches.

GARDEN HELP: For more planting information, or if you are having plant, tree or lawn problems, please call the MASTER GARDENER HELPLINE (609-989-6853), Monday through Friday from 9:00 a.m. to 3:00 p.m. You can also visit our website at www.mgofmc.org for more information from the Rutgers Cooperative Extension and Barbara J. Bromley.

Looking for inspiration? Stop by Mercer County Educational Gardens which feature a variety of beautiful plants– all of which are proven to thrive in our area. (Photo by Joe Scarlata)

GARDEN INSPIRATION: Don’t forget to visit our Educational Gardens  this summer when the gardens are in their full glory, the flowers are in bloom and the butterflies are visiting.  For information about coming activities, check out our Events page.

Happy planting!

More info:

Basics of Flower Gardening

Planting High Visibility Flower Beds

10+ Most Common Gardening Mistakes


Jumpstarting Spring: Starting Seeds Indoors

After enduring months of bleak outdoor landscapes, the long ramp up to spring can be tough on gardeners — leaving us itching to get our hands in the dirt and just plant something. Inhospitable as the outdoors may still be for tender plants, there is a tried and true antidote for gardeners’ particular brand of spring fever: sowing seeds indoors.

Annuals get a great head start on flowering when they begin life indoors. Pictured above are ‘Profusion’ zinnia, which are very easy to grow from seed–even for beginners.  (Photo by Elena Kyuchukova)

Cold Comfort: The advantages of seeds

Starting seeds indoors offers some significant benefits.  For one thing, buying seeds is a lot cheaper than buying plants, allowing you to indulge in those dramatic mass plantings and deep drifts you’ve been dreaming of –without breaking the bank.  For a minimal investment in a packet of seeds, you can populate your garden with plenty of new plants –and have enough left over to share with friends and fellow gardeners!

Seeds also afford you the opportunity to try out new or exotic varieties that you won’t find in mass market outlets or local garden centers.  Retail space is always at a premium, but especially in springtime. So plant purveyors tend to focus on a limited number to “regulars” that they know will sell.  By raising your own plants from seed, you give yourself a wider palette of plants to work with.

Given our somewhat short growing season here in the Mid Atlantic, jump starting plants inside can also nudge slow starters into earlier bloom and allow vegetables that wouldn’t ordinarily grow in our region enough time to mature.

The sleeping potential contained in each seed has the power to transform your garden –and your outlook– without blowing your budget.

In addition to all these good and practical reasons for starting seeds, if you ask veteran seed-starters why they do it, they will often tell you that there is just something magical about planting a small, hard fleck of possibility and watching it grow into a supple, living shoot.  No matter how many times you’ve experienced it, they’ll say, it never ceases to amaze.  So, if you haven’t tried it before, now is great time to start.  And if you have, well… it’s time to get growing!

Sow What? Plan before you plant

When it comes to choosing which plants to grow from seeds, the sheer volume can be overwhelming.  And every year, new and exciting hybrids and varieties are added to the mix.  Combine this with page after page of luscious photos and glowing descriptions, and you have a recipe for overbuying.  So, if you’re new to seeds, starting small is key.

But it behooves both rookies and veterans alike to take a close look at their garden before buying, and come up with some kind of plan – one that takes into consideration how much space you have and the conditions in your garden. (For help with planning, see: Basics of Flower Gardening and Planning a Vegetable Garden  from Rutgers.)

And don’t forget to take into account how much time (and space) you have inside for growing all those seeds…

Once you’ve established your limits, there are as many ways to research seeds  as there are gardeners. Whether you enjoy pouring over seed catalogs, watching gardening shows, or developing your Pinterest board–the time you invest in planning your seed-starting endeavor will end up saving you time, effort and cash later on.

Don’t pitch those packets! Seed envelopes contain everything you need to know about how to sow and grow the seeds inside.

Pushing the Envelope: Reading seed packets

As you peruse the wide selection of seeds available online and in garden stores at this time of year, take a minute to read the packets and/or accompanying plant descriptions. You’ll find they contain a lot of important information, some of which might be unfamiliar to gardeners new to seed starting.

When selecting vegetable varieties for example, check packets for the number of days until harvest to be sure your choices will ripen before frost. Many long-season vegetables must be started indoors in early spring. Similarly, many annual flowers need an indoor start if they are to bloom during the summer.

For detailed info on deciphering seed-starting lingo, check out: How to Read Seed Packets and Information on Seed Packets.

To get the most out of the information provided on seed packets, there are several pieces of information you need to know. One is your USDA Plant Hardiness Zone, which often appears as a map with designated planting dates. Mercer County gardens are in either Zone 6b or 7a, depending on their location. To find out for sure which zone your garden falls into,  just enter your zip code on the USDA website here: Find Your Plant Hardiness Zone.

Timing is Everything: Picking the perfect time to start seeds

When it comes to determining the proper time to start your seeds, there are two important dates to know:

  1. The average LAST frost date for your area ( the date in the spring when you can finally be sure that you won’t get another frost)
  2. The average FIRST frost date in your area (the date in the fall when frost is likely to start killing sensitive plants).

Here in Central New Jersey, our average last frost date is May 10.  To be on the safe side, a good rule of thumb has always been to wait until after Mother’s Day to plant seedlings outdoors.

Our first frost is usually on or about October 15which is important to know when growing certain vegetables from seed, to make sure they’ll have enough time to fully ripen before frost. (Rutgers Fact sheet Starting Vegetable Seeds Indoors lists how many weeks pass between seeding indoors and when transplants are ready for planting in your garden.)

Starting seeds at the right time helps seedlings develop into sturdy, well-branched plants, like these coleus, (Plectranthus scutellarioides.) Since coleus likes warm weather, plants started indoors should be planted outside 1-2 weeks after the last frost date. (Photo by Elena Kyuchukova)

A common mistake new seed starters often make is starting seeds too early.  If started too soon,  plants tend to have spindly growth and may outgrow their containers before it is warm enough to transfer them outdoors.  The goal is to produce stocky, moderately sized plants that will recover quickly when planted outdoors.  To achieve this, it’s critical to start seeds at the proper time.

It All Adds Up: Seed starting math

To determine when to start your seeds, look on the back of your seed packet for the average number of weeks required to grow indoors or transplant outside, as well as the number of days to germination.  (These two numbers are often listed as a range.)  Add  the time required for germination and time indoors to transplant.  Then, on a calendar, count backward the appropriate number of weeks from your last frost date.  The result will be the appropriate date for starting that type of seed.  For an example, see below:

‘African Sunset’ petunias

The Annual Garden at Mercer Educational Gardens in Pennington  will include ‘African Sunset’ Petunias grown from seed this season.  

To determine the best time to start them indoors, Mercer County Master Gardeners took the “8 weeks indoors” listed on the back of the seed packet, and added the listed “7 days needed to germinate,”  for a total indoor growing time of 9 weeks (1 week to germinate + 8 weeks indoors.)

They then counted 9 weeks back  from our last frost date of May 10, and arrived at a seed start date of March 8.


Down to Earth: Soil for starting seeds

Seeds should be planted in clean, fine potting soil– generally no deeper than the width of the seed itself. (Photo by Margaret Montplaisir)

Choosing the right potting soil is another important part of successful indoor seed starting. The most convenient choice is to purchase a commercially available soilless mix, one specially formulated for starting seeds. Most contain a mix of peat moss, perlite, vermiculite, and usually some fertilizer. Soilless mixes are also sterile and reduce the risk of losing seedlings to soil-borne diseases.

You can create your own seed starting mix too (a recipe is contained in Rutgers fact sheet Starting Vegetable Seeds Indoors ) but know that using soil directly from the garden is not recommended, because it may contain insects, weed seeds, or disease organisms that could damage or kill young plants.

Pot luck: Choosing containers for seedlings

Peat pots can be planted directly into the garden, which keeps developing roots intact. But make sure the edges of the pot do not stick up above the soil, since the exposed area will act as a wick and cause moisture to evaporate rapidly from the pot.

Almost any clean container can be used for starting seeds provided it’s at least 2 inches deep and allows for good drainage.

Some gardeners like to save money by reusing yogurt containers, milk cartons, aluminum pans, and clear clamshells from the produce department. A 6-ounce plastic, non-waxed, paper drinking cup also makes an easy and inexpensive starter container.  Before using for up-cycled containers for seeds, be sure to poke some holes in the bottom to allow for proper drainage. Otherwise, soil can become saturated, which encourages diseases in the seedlings. One way to minimize the chance of overwatering seedlings, is to be sure to start them in small containers.
In addition to using recycled containers, there are a lot of choices available for purchase, including:

  • Plastic trays (flats) that are 10.5 in. X 21 in. X 2 in. deep
  • Small pots and pellets that expand when you add water made of compressed peat
  • Plastic cell packs (inserts or market packs) with square or rectangular plastic cells joined together and sized to fit into a plastic flat. The individual cells range in size from ½  to 4 inches in diameter
  • Plug trays in sturdy one-piece plastic flats that are divided into individual cells

Hit the Dirt: Planting how-to’s

Regardless of the type of container you choose, fill it three quarters full with seed-starting mix and sow the seeds. Be sure to place seeds at the planting depth recommended on the seed packet. Plant one or two seeds per individual container or, if using flats, you can plant in rows that can be thinned or transplanted into individual containers following germination.  Be sure to label the flats to avoid confusion, using a pencil or water-resistant marker.  (It’s easy to forget which sprouts are which.)

When seeding a tray or flat, plant in shallow rows 1 to 2 inches apart. Sow the seeds uniformly and thinly in the rows. Be sure to label each row right away with plant type, variety and date of planting.

Water Ways:  Keeping seedlings moist

Once the seeds have been planted, the container should be watered from the bottom by placing it in a shallow pan of water and waiting until the surface of the mix is moist. This method avoids overhead sprinkling, which can carry away smaller seeds.  The pot should then be removed from the pan and allowed to drain.

It is important to keep the soil moist at all times, watering again from the bottom as necessary since seeds and seedlings are extremely sensitive to drying out.

Placing the container in a clear, plastic storage bag until seedlings emerge will help keep the soil moist. This will also increase the humidity and help keep temperature stable. The plastic should not be in contact with the soil, though. Be sure to remove the plastic cover as soon as sprouts appear.

A Fungus Among Us: The danger of damping-off

While seedlings should be kept moist, they should never be kept continuously soaking wet, since this condition can lead to “damping-off,” a fungus disease that is deadly to young plants. The fungi that causes the disease – –PythiumPhytophthora and Rhizoctonia– – can quickly kill an entire batch of seedlings.  If an infection occurs, dispose of the plants and growing medium, wash containers and tools to remove any debris, and soak them for 1-2 minutes in a solution of 1 part chlorine bleach to 10 parts water.  Then rinse with clean water.

The  Heat is On:  Keeping seeds warm

The consistent warmth provided by electric heating mats –like the black and green one visible above– can be very beneficial to certain types of seedlings, leading to better germination rates and stronger root systems. (Photo by Ellen Kellich)

In addition to moisture, seeds need warmth to germinate. For the best results, keep seedling pots in a location that is between 70 to 75 degrees F.  Spots like the top of a hot water heater or the top of the refrigerator offer enough warmth to aid germination.

Or you can purchase heating mats that are specially designed keep germinating seeds warm. You can find them in larger garden centers, and online. Be sure to only use mats that are designed for seed germination and follow manufacturer’s directions carefully. Using a thermometer or thermostat in conjunction with seed mats will prevent overheating seeds and soil.

Let there be Light: Simulating spring sun

Better results stem from growing seedlings under fluorescent lights( rather than to relying on natural light alone.) Lights should be positioned very close to seedlings –2 to 4 inches above them is best. (Photo by Ellen Kellich)

Once the seedlings emerge, remove plastic bags or covers and give the seedlings as much light as possible so they can grow into stocky well-branched plants.

While it’s possible to grow seedlings without supplemental lighting, the fact is: you will have much better success growing under lights compared to relying solely on natural light from windows.

There are many types of lights that can be used to grow seedlings indoors. They range from fluorescent “shop lights” to the newer LED light systems.  What’s best for you depends on your space and budget.  For the most part, standard fixtures with a combination of cool white and natural daylight tubes provide adequate light are relatively inexpensive.

It’s important to keep lights no more than 4 inches above the tops of your seedlings. As close as 2 inches is ideal. Lack of light is the major cause of elongated, skinny stems which results in frail and floppy plants. Hanging lights from chains or pulleys makes it easier to keep them at the optimal distance as plants grow.

Plants need 12 to 16 hours of light daily, but don’t leave lights on all the time.  Plants need some dark periods too for proper development. Adding an inexpensive timer to your light set up can help ensure plants get the right amount of light and darkness.

Numerous plans for easy-to-build light stands are available online, including this from University of Maine’s Cooperative Extension: Bulletin #2751, Starting Seeds at Home  and this Do-It-Yourself PVC table-top light stand from the University of Maryland.

Room to Grow: Moving seedlings to larger containers

As seedlings grow, they must be potted up into larger containers to give them enough space to develop. Avoid the common mistakes of keeping seedlings in flats too long, which can hinder their growth.

The ideal time to transplant young seedlings is when they are small and there is less danger of setbacks from root shock. This is usually about the time the first “true leaves” appear above or between the “cotyledon” or “seed” leaves, which are the first leaves to appear. (The seed leaves  are visible in the photo below.)

Dig the seedlings out of the mix with a small trowel or spoon. When transplanting, always handle the seedlings by the leaves, being careful not to damage the fragile seedling stem or root system. Then transplant them gently into their new containers.

When planting in flats, like these parsley plants, seeds can be planted in rows. Once each plant has four leaves, thin seedlings by pulling out all but the healthiest plant. (Photo by Ellen Kellich)

Ready for the Great Outdoors: Hardening off

Seedlings are ready to transplant outdoors when their roots have filled the pot in which they are growing. Check instructions on the seed package for any specific details on when and how to transplant.

Before planting the seedlings in your garden, allow at least a week for them to become adjusted to the outdoors. Each day, place them outside in a sunny spot for a few hours, and then bring them back inside. Gradually increase their length of time outside.

It’s best not to set out tender seedlings on windy days or when temperatures dip below 45 degrees F.  Even cold-hardy plants will be hurt if exposed to dramatically colder outdoor temperatures.

After a week, seedlings should have adjusted sufficiently to the outside world to be ready for planting in the garden. When planting seedlings outside, pay attention to the spacing indicated on the seed packet.

Seedlings should be planted at the same depth at which they were growing indoors, except for tomatoes, which may be planted deeper.   For more info on planting vegetable seedlings, see the Rutgers fact sheet Planning a Vegetable Garden FS129.

If possible, try to transplant on a cloudy day to minimize wilting or transplant shock. Once the seedlings are in the ground, firm the soil around the root ball, and water immediately with a solution of water and starter fertilizer.

After about 6 weeks indoors, these beautiful kale plants are ready for the real world.  (Photo by Elena Kyuchukova)

Seeing is Believing: Stellar seed starting videos

For great step by step seed starting videos, check out these featuring University of Maryland Master Gardener, Kent Phillip:

Seed Starting: Part 1 – Timeline

Seed Starting: Part 2 – Materials

Seed Starting: Part 3 – Planting

Seed Starting: Part 4 – Care of Seedlings

Seed Starting: Part 5 – Transplanting