Starting Plants From Seed

When mail-order catalogs and local garden centers are bursting with a dizzying array of seedlings of all kinds, why would anyone want to bother starting their own plants from seed? Because starting plants from seed is less expensive; there are more varieties to choose from; you can grow higher-quality plants suited to your schedule; and you will enjoy the simple satisfaction of growing your own seedlings.

To be successful, you’ll need to provide the right conditions for good germination and healthy growth. Here are the basics:

Choosing the Best Seedling Pots

You can start your seeds in almost any type of container as long as it has drainage holes and is at least 2 to 3 inches deep. There are many different seed starting containers on the market, including peat flats, jiffy pellets and the new, “Cow Pots”. Cow Pots are compostable seed starting pots made from cow manure. For tomatoes and peppers, you may want to start your plants in small seed starting flats and move them to larger containers as they outgrow the smaller ones. These plants can get large and need more leg room before the weather is ready for them to move out to the garden. Some gardeners always plant their seeds in small rows in a larger flat. Once they are up, separate and replant into individual containers.
Four reasons starting your own plants from seed is a good idea. Click To Tweet
An eco-friendly way to make pots! With just a twist of the wrist anyone can make home-made seedling pots. Newspaper strips are rolled around the “press” and twisted into the pot-form. Pots slip off the press ready to be filled with soil and plants. Pots remain strong even as plants grow and as roots penetrate the walls.

Choosing the Best Seed Planting Mix

Many seeds do okay sown directly into ordinary garden soil, but even good soil may be poor in pots or flats.
To give your seedlings premium growing conditions, and to help avoid insect and disease issues, seeds are better started in a prepared growing mix, not in your garden soil. A good mix is a moist and spongy blend of sphagnum moss, vermiculite and perlite. The texture should be readily friable and finer the texture the better. If you can find a mix containing Mycorrhiza you will improve transplant survival and improve growth all around.

I have used Premier Horticulture’s Pro Mix HP Biofungicide and Mycorrhizae for years and it is an excellent product.

You can purchase a prepared potting mix, or mix your own, using 1/3 vermiculite, 1/3 perlite, 1/3 fine chopped sphagnum moss. Prepared seedling mixes contain precious little, if any, “soil food”. The newborn seedlings will need to begin being fed with a weak fertilizer solution as soon as they germinate, and continue to feed them weekly until you transplant them into the garden.

Once your seedlings are sprouted and growing, you can transplant them into larger containers, you can add compost or garden soil to the original blend. This will provide some beneficial nutrients, and will help your seedlings get used to the bacteria and other microorganisms they will soon experience in the garden.

Keeping Track of your Seedlings

Different seeds germinate and begin to break the ground’s surface at different rates, so timing is key. Some seeds, like onion, leek, and celery need to be started 12 weeks before they are transplanted into the garden. Others, including cucumbers and sunflowers, need only three or four weeks before transplant time. If you start them much earlier they will get leggy and weak. Read your seeds’ planting instructions to find the grower’s recommended seed starting times. If you plan to start more than a packet or two of seeds, it helps to chart out a weekly seed starting schedule, counting back from the date you plan to plant seedlings.

If you will be growing your seedlings in a greenhouse or a very warm room, you should subtract at least a week from the recommended planting date. Heat promotes faster growth, and you may find yourself with giant plants that are ready to be put out into the garden before warm weather arrives.

Seedlings that are started very early may need to be transplanted into larger containers after three or four weeks. This is especially true if you broadcast your seeds in flats rather than planting them in individual growing cells. The sooner your plants are put into individual cells with plenty of root space, the happier they will be. You will also lessen the risk of tearing too much of the root systems apart while separating.

For more on how to create a customized seed starting schedule, see When to Start Seeds.

Planting and Caring for Your Seedlings

The seedling pots should be watered completely before it is placed in your seed starting containers. Fill your prepared pots or trays to within 1/4 to 1/2 inch of the top. Now, at last you are ready to sow your seeds. Take one last look at the seed packet for any special information about seed stratification, pre-chilling, pre-soaking, light preferences, or special temperature requirements.

Seeds can either be scattered on the soil surface or planted into individual pots. Resist the temptation to sow too thickly. Most seeds should be covered with a fine layer of soil. Unless the seeds require light to germinate (such as snapdragons), or are too tiny to tolerate being covered (such as petunias), you should cover the seeds to about three times their thickness.

Water your seedling pots gently so you don’t jostle the seeds around or knock them out of the pot altogether (it is easy to do!) This also helps make sure there is good contact between the seed soil. Label each flat, row, or container with a wooden marker so you will remember what they are later. Even if you are good at recognizing the peppers from the tomatoes it is always wise to keep track of your variety, when you planted, etc so you can determine what you would like to use again and what didn’t work out so well for you. I also keep the seed packet, for future reference, in my garden folder.

ideal germination temperatures

Temperatures for Seed Germination

The most favorable temperatures for germination should be listed on your seed packets and indicate soil temperature, not air temperature. Though some seeds will germinate best at a soil temperature of 60° F (16.6° C), and some at 85 (29.5°C) degrees, most prefer an average temperature of about 78°F (25.6°C).

In the winter, many vegetable seeds are slow to emerge. When seed sits in the cold soil it often starts to decay rather than germinate and produce seedlings. You may be tempted to believe the seed is to blame for the problem. More often low temperatures are at fault.

If the soil is too cold, seeds may take much longer to spout. They may not germinate at all. Here are a few examples…

Soil Temperature
Vegetable 41° 50° 59° 68° 77° 86°
Asparagus NG 53 24 15 10 12
Beet 42 17 6 5 5 4
Cabbage / 15 9 6 5 4
Cantaloupe / / / 8 4 3
Carrot 51 17 10 7 6 6
Cucumber NG NG 13 6 4 3
Lettuce 15 7 4 3 2 3
Parsley / 29 17 14 13 12
Peppers NG NG 25 13 8 8
Sweet Corn NG 32 12 7 4 4
Tomatoes NG 43 14 8 6 6
*planting depth = 0.5 inches; NG = no germination; / = not tested; Source: Harringtion, J.F. and P.A.Minges, Vegetable Seed Germination. California Agricultural Extension Mimeo Leaflet (1954).

To provide much needed warmth to encourage the best outcome, you can set your seedling flats on top of a warm refrigerator or purchase a specialty heat mat. The most important thing is keeping them in a warm until the seeds germinate. After they break the soil surface get the seedlings under light.

After they germinate, most seedlings will grow best if the air temperature is below 70°F (21°C). If the temperature is too warm, the seedlings will grow too fast and get “long legs”. This will weaken their chance for surviving transplant shock. Most seedlings will survive just peachy in air temperatures as low as 50°F (10°C), so long as their soil temperature stays around 65 to 70°F (21 to 18.3°C). You can keep the soil warm by using a special designed heat mat which warms root area 10 to 20° over ambient air temperature to improve seed germination. Keep an eye on the soil temperature with a soil thermometer.

Light for Growing Seedlings

There are not many seeds that require light to actually germinate, but as soon as they sprout, they need to be placed in a window that gets maximum sun exposure or under grow lights that are designed for growing plants. Check your seeds daily. Seeds that germinate and grow above soil level without enough light will become tall and leggy — a condition that is almost impossible to correct.

To produce the food needed for optimal growth, most seedlings require 12 to 14 hours of direct light. The commonly seen tendency to grow leggy (long stems that often fall over and die) that often occurs when seedlings are grown on a windowsill and loudly announces “WE ARE NOT GETTING ENOUGH LIGHT!” or enough hours of light, anyway. If your seedlings are in a south-facing (in the northern hemisphere) window, you can improve the light received by covering a piece of cardboard with aluminum foil and setting it in back of the seedlings to reflect incoming light almost doubling the amount of light received.

seed starting using grow lights
Grow lights are full daylight spectrum color-balanced bulbs to promote growth.

If you do not have a south-facing window, you will need to use artificial lights. When growing seedlings under lights, you can use a combination of cool and warm fluorescents, or full daylight spectrum bulbs. The familiar incandescent bulb that lights our homes produces too much heat in relation to the light given off. It also lacks the blue-spectrum light that keeps seedlings stocky and dark green.

Seedlings need a high intensity of light. The bulbs should be placed very close to the plants — no more than three inches away from the foliage – and should be left on for 12 to 14 hours per day. If you are growing your seedlings on a windowsill, you may need to supplement with a few hours of artificial light, especially during the winter months.

Watering Seeds and Seedlings

Germination requires consistent moisture. It is important that the soil be kept moist but not soggy to prevent the seeds from rotting. There are different ways to achieve this. Some gardeners cover their flats with clear plastic until the seeds germinate. Some seed starting systems, have a plastic cover to help retain moisture

As soon as your seeds have sprouted, remove coverings to cut down on moisture and humidity levels. Check the soil every day to ensure that it is moist, but not wet. Too much moisture will hinder growth of the seedling’s roots and cause disease. Let the soil dry some between watering time. This will help prevent mold and fungus from starting.

The seedlings will be much healthier if you water them with room-temperature water instead than ice-cold water. If use a chlorinated water, fill an open topped container and allow water to sit overnight. Chlorine is a gas that will evaporate if left open to “breath”. The sodium used in common water softeners can easily kill your seedlings. Don’t use it.Try to make sure that water reaches to the bottom of the growing container so the seedlings’ roots will stretch out and create a deep healthy root ball. If your setup allows, water from the bottom.

Air and Humidity for Seed Starting

Most seedlings thrive in a humidity level of 50 to 70 percent. Poor air circulation and high humidity levels and poor air circulation can lead to fungus growth on the surface of the soil and can cause disease. If you have a difficult time keeping the humidity level high enough, you can place an inch or so of sand or small pebbles in a waterproof tray. If seedlings are in a small room, consider keeping a small fan going to keep the air circulating.

Fertilizing Seedlings

After the seedlings develop their second set of true leaves, it is time to start feeding them, but young seedlings are very tender and cannot endure a full portion. Only apply less than half of what you would a grown plant dose until they are three or four weeks old. After that, treat them as you would any plant using full-strength fertilizer every few weeks. Unless you chose to use plain garden soil, the mixes mentioned above contain very little “plant food”, so feeding them is extremely important. Since you want the best possible, use an organic fertilizer.

Thinning and Re-potting

Depending on what you are growing, you may have to transplant seedlings into larger pots if they start to get crowded and it’s still too early to put them outdoors. Especially if you planted seed in an open flat, do not wait for the plants to become a mass of roots and stems. The less you rip and tear, the better the seedlings will weather the transition. When handling tiny seedlings, hold them by their leaves or roots. Avoid holding them by their stems, which are fragile and can be quite easily crushed or bent. Handle with care!

Stems and roots are easier to separate when the soil slightly dry and not really wet. Take out a lump of seedlings and separate as you go. Use a spoon or your fingers to transplant individual plants. If the seedling is slightly leggy, repot it a little bit deeper than it was previously growing. Otherwise, re-pot at the same depth. Tomato seedlings, leggy or not will benefit from a different approach. You can give a BIG boost to tomato seedlings if you remove all but the top few leaves. I know it sounds hard, but if you do this and bury the
stem deep into the pot new roots will grow where the removed stems are located under the soil. This will help promote a good strong root system for hearty healthy tomatoes. When your seedlings have been re-potted, water them well, feed them and return them to their grow light or sunny windowsill.

Transplanting Seedlings

The weather has warmed up! The moment we have all been waiting for! It is time to “harden off” your seedlings by gradually exposing them to their fabulous new home. Your seedlings have been coddled inside with steady water, light, humidity and (hopefully) temperature up until now. They are NOT tough. The great outdoors is not so consistent or predictable, particularly in the spring!

Hardening off, while a pain in the behind is a necessary part of growing your own seeds. At least one week before you expect to transplant seedlings, begin reducing the amount of water and food you give them. Put the seedlings outside for an hour or so every day, first to allow for temperature acclimation, and eventually to the difference in light. Gradually increase the amount of time they spend outdoors and in the sun, being careful to protect them from too much wind and hot sun. The new light source can kill transplants in a matter of hours, so
when placing them outside, be sure to account for where the sun “will be” later.

Seasoned gardeners will tell you that transplanting should be done on an overcast or “almost rainy” day when there is only slight wind. Row covers or shade fabric can help make the transplanting more successful. This will help keep transplants safe from butterflies and moths looking to lay eggs (that turn into wormy nuisances) and speaking of a nuisance neighborhood cats find newly transplanted areas as intoxicating as catnip, puppies find it hard to resist as well. Since flea beetles (especially on brassicas) cannot be excluded from the list I
guess you can see why many experienced gardeners swear by them to prevent intrusion on many fronts. Be sure that you water well to settle roots in well.

What to Feed Seedlings

Worm Castings (worm compost) Soon to be known as the “World’s Greatest Organic Fertilizer!”

The simple fact is that earthworm castings were created by nature for the purpose of promoting optimum plant growth and everything required to provide it, is found in them. When you concentrate this odorless, non-burning miracle of nature in greater concentrations than usually found in nature, the results are truly spectacular.

Complete fertilizers

Luckily there are more and more liquid organic fertilizers available, although they can still be hard to locate. A mix of fish emulsion and kelp has always kept my seedlings growing. Another option is to mix a granular organic fertilizer into the soil, when you “pot up“.

Compost Tea
Compost tea is liquid slurry of compost ingredients which contains and promotes beneficial organisms, active and dormant, that exists, or used to exist, in your landscape. This is not a new process. In fact, compost tea has been around for centuries. Compost tea should be 100% organic. You can even “brew your own” with compost tea bags!

Homemade Organic Plant Food Tea

Homemade organic plant food tea is made by infusing a coffee can full of dried manure in a 5-gallon pail of water and allowing it to set for 3 to 5 days. Strain the tea and spray it on the garden area. Another organic plant tea can be made by coarsely chopping fresh nettles or loveage and adding approximately 2 lbs.
of the greens for every gallon of water. Allow the mixture to set for 2 to 3 weeks and strain. This tea can be mixed into compost that will make a rich plant food for the garden. As an added benefit, this mixture will attract lady bugs and butterflies to the garden area making it a perfect choice for flower beds.

Seaweed/kelp extracts

The effect and kelp has on plants is said to be magical, if not, it has been well documented. It seems to be particularly effective on seedlings, promoting vigor, cold hardiness, and pest and disease resistance. Apply a dilute amount to the soil or leaves several times during seedling growth before hardening off and at transplanting time. Kelp is not considered a fertilizer, because it does not provide major nutrients. Kelp should always be used in combination with a complete organic fertilizer.

Fish emulsion
Fish emulsion is excellent source of trace minerals, as well as micro and macro-nutrients. It can be smelly, so be cautious about using it indoors. Ideal for young seedlings during their first few weeks in the garden.

If you have any questions, contact me! I am here to help. 🙂

More Articles on Saving Seeds and Seed Starting

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