Starting Vegetable Plants from Seed

By: Roxanne DiRaimondo

Spring is in the air and every gardener is thinking about what to grow this season. Here in New Jersey, we cannot really plant our vegetable gardens until after the last frost date, usually around May 15.

If you normally buy your vegetable plants already started, you will still have to wait a while for that.

But, if you would like to start some of your plants from seed, indoors, you can actually start on that right now! The key is knowing when and how to get started.

Growing Medium

One of the first things to know about sowing seeds for vegetable plants, is that you NEVER start them out in any kind of soil.  The reason? The soil is too heavy, and it may contain weed seed and/or disease.

The correct medium for growing seed is usually a mix of sphagnum moss and vermiculite, or peat and perlite. These are sold commercially under several brands, such as Miracle Gro, Burpee, Jiffy and others, and are listed on the bag as “seed starting mix.”

Growing Containers

Once you purchase the seed starting mix, what containers can you use to plant the seeds in? Well, it depends on what your needs are.

If you are growing numerous amounts of plants, you may want to use plastic trays that can accommodate anywhere from 15 -50 or more cells in them. These are sold in many places and online, and are not usually very expensive.  

However, if you want to seed smaller amounts of plants, and/or keep costs to a minimum, you can also use many things you might already have around the house, such as plastic cups, yogurt containers, leftover plant containers you have from last year, or something similar.

The key is that the container has to be at least 2 inches deep, have good drainage and be thoroughly sanitized before use. A 10% bleach solution will usually do the trick to clean containers properly.

Commercially purchased containers usually come with pre-made drainage holes, and often also with plastic trays that fit underneath them to collect any drainage. If you are using something from around your home however, you will still need drainage, and can accomplish that by simply poking a few holes in the bottom of your container. You will also have to put something underneath your container to catch excess water, and, really, any type of plastic plate, lid or tray will do, as long as it is deep enough to hold the drainage.

The last item you will need for your container is something to cover the seed with until it germinates, sort of creating a mini “greenhouse” effect. Many of the commercially purchased containers come with plastic lids for that purpose, but if you are using a smaller container or something from around the house, a Ziploc bag can do the job. Just place the bag over the container, use plastic labeling sticks, popsicle sticks or something similar to keep the bag propped up and not directly touching the container surface. Do not zip it all the way closed; leave it partially open to allow for air flow

Temperature

Seeds need the proper medium as well as light, warmth and water to germinate. Here in New Jersey, it is usually pretty cold outside when we begin to seed plants indoors. So how to keep them warm until germination?

One popular way is to purchase a heating mat. These mats heat the tray or container from the bottom, and can be set to 65 and 80 degrees depending upon the requirements of the seed. The trick is to remember to remove the mat once the seed has germinated. If you don’t have a heating mat, you can put your seeds near a heat vent, or on top of an appliance, such as a refrigerator, on top of radiator or furnace, or similar places where heat is generated. Just be careful it does not get too hot which will ruin the seeds.

A rule of thumb is that the room you are using for germination should be around 68-80 degrees. If seeds are kept at that temperature, they may not have to have a heating mat or any other special equipment to germinate. The planting medium itself should be kept at 70-75 degrees.

Once germinated, the seeds need to come off of the heating source and the plastic cover/Ziploc bags need to be removed. The plant will need good air circulation at that point.

Light

Once germinated, your seedlings will need light to grow. Grow lights don’t need to be anything fancy. An  LED or fluorescent light fixture that’s labeled “full spectrum” can usually be purchased fairly inexpensively at a home center.

The light source needs to be adjustable. Ideally, the light should sit about 4 to 6 inches above the seedlings.  As the plants grow, you can keep raising the light to keep them at that spacing.

The lights really need to stay on 14-16 hours a day. You can put them on a timer or just set a schedule for yourself.

What about actual sunlight? Sometimes, if a gardener does not have any special type of “grow light,” he/she will put the germinated seedlings in a sunny area or windowsill to continue growing. While it is possible to keep the seedlings growing this way, it is not considered ideal. The plants tend to end up as somewhat leggy and not as strong from constantly leaning to get enough light each day.

When and How to Sow the Seeds

The seed packet is your friend! Look for information on the packet which will tell you the recommended time before the last frost date to plant your seed. A basic rule is that most annual vegetables should be sown indoors about six weeks before the last frost in your geographic area.

The packet will also tell you what depths your seed should be planted in, and how many seeds should be planted in each cell or container.

The best way to start is to wet the amount of seed starting mix you will need before you begin.

Then, fill your cell or container with the damp seed starting mix to the top. Tamp it down a bit and level it off.

Next, open the seed packet but do not touch the seeds with your hands. Use a small notecard folded in half as holder for your seeds. Use a pencil or wooden skewer to make a slight depression or furrow in the medium, then gently tap the seed from the card into the depression or furrow. Cover the seed with medium.

As soon as you are done, label, label, label! Stick a label on the outside of the container listing what you have sown and when. Also use a plant stick or popsicle stick, and write the information on there as well, and put that into your container or tray.

Then, using a mist sprayer, gently spray what you have sown.

As the seedlings germinate and grow, you will have to check them each day to make sure they do not dry out. Water and/or mist as necessary. Do not overwater.

When and How to Move Your Plants Outside

Photo: Lettuce transplanted outside.

The goal of all of this seeding, of course, is to grow plants that can eventually be planted outdoors after the last frost date.

After the last frost date, and about a week before you are ready to plant your plants in your garden, start taking them out each day and set them in a cold frame, covered porch or other protected structure. This will allow them to get acclimated to outside conditions. Do not take them out on days when temperatures are below 55, or there is heavy rain or other poor weather conditions.

After that, planting can begin! Good Luck!