I really love starting seeds indoors because there is such a joy when the seedlings emerge. Next, watching as the seedling matures enough to be planted is equally rewarding. Finally, the biggest excitement, of course, is from either harvesting a food you have grown or seeing a beautiful flower develop. In addition, I like having complete control over how much I plant and when I plant. In this post and accompanying video, I discuss three aspects of starting plants from seeds: supplies needed, the planting process, and caring for seedlings.
Before I get started on these topics, I want to mention planning. Whether you are planting one variety of seed or multiple varieties, planning will help you know what to expect at various points in time. I invite you to reference my blog titled “How to create a simple crop management plan” for information and resources on planning. Good planning will also ensure that you don’t start your seeds too early, something that I was guilty of when I first began seed starting.
“Nothing great was ever achieved without enthusiasm.”
Ralph Waldo Emerson
SUPPLIES
Here is a list of the key supplies that you will need.
1. SEEDS
Start with fresh quality seeds that have been packaged for the current growing year. However, it is possible to use seeds as old as five years. Just beware, the germination percentage (e.g. number of seeds that will sprout into seedlings) will go down the older the seed gets. The seed packet has lots of information that will help you with planning. There are three key date related pieces of information that you may find on a seed packet (I say ‘may’ because each seed company provides different pieces of information).
Seed Packet Date Information
- Days to germination – this is an estimate of how long it will take for the seed to sprout. For planning purposes, just add these days to the date that you planted the seed. When I plan, I always use the higher number in the range (then I am pleasantly surprised when the seed exceeds my expectations).
- Days to harvest/bloom – this is an estimate of how long it will take for the vegetable/herb to reach maturity or for a flower to bloom. Again, take the highest number of days for planning purposes. The days to harvest should be added to the transplant date to get the best estimate of when you will be able to harvest.
- When to sow outdoors – some seed packets will show a map of the United States and indicate (by month) when it is appropriate to plant seeds or place transplants outside. This is usually based upon frost dates in your area. For example, I live in NJ in zone 6a. If I put my zip code into the Farmer’s Almanac planting calendar it tells me there is a 30% chance that the last frost date will be April 28th (in 2019). This tool will also provide recommendations for when to start seedlings (by vegetable) and when to transplant.
2. GROWING MEDIUM
This is the mixture you will use to plant the seeds. It’s important that you purchase a quality growing medium. There are commercially available mixtures, specifically formulated for starting seeds, that you can purchase for a reasonable price. Many of these mixes are referred to as ‘soilless’ which means, as the name implies, there is no soil. These soilless mixes ensure that no bacteria or fungi are introduced into the medium. In addition, these mixes are usually made up of some combination of peat, coconut coir, perlite and/or vermiculite. When you open the bag, there should be a pleasant earthy smell and the mixture should be light and fluffy. The mixtures may also contain lime (for ph adjustment) and macro-nutrients (nitrogen, potassium, phosphorus) and micro-nutrients (chlorine, copper, iron, manganese).
It’s important to read and understand the contents of your mixture so that you will know how to care for the seedling. If there are nutrients in the mixture, then additional fertilization may not be necessary.
When choosing your growing medium, I recommend that you use a medium specifically indicated for seed starting
3. PLANTING CONTAINER
This is where you have the most flexibility. Just about any container can be used if there is good drainage in the bottom. Plastic trays are my favorite for three reasons: reuse, there is a water-catching tray, and there is a dome.
Various types of containers
4. PLANT LABEL
After you plant your seeds, label what you planted. You can be creative and make your own or you can purchase plant markers as shown.
Plastic plant labelling sticks
SEED PLANTING PROCESS
Here is the six-step process that I follow when planting seeds.
1. WET THE GROWING MEDIUM
Start by wetting the growing medium you will be using. I use a bucket and put as much mixture as I will need into the bucket. Then add water, a little at a time until the mixture is moist but not soggy.
Add water to the growing medium prior to planting seeds
2. FILL PLANTING CONTAINER
Fill the planting container with the growing medium and gently compact down, you want a good foundation into which to plant your seed.
3. PLANT SEEDS
The seed packet may indicate the ‘seed planting depth’, check your packet and plant accordingly. I use a folded legal size envelope and a toothpick to assist with planting seeds. I have found this so much easier than using my palms and other seed planting devices. Here is my process that is demonstrated in the video.
- Fold the envelope in half lengthwise
- Pour some seeds from the seed packet into the crease of the envelope
- Using a toothpick, gently separate the seeds and plant 2-3 seeds in each cell (if using a cell flat).
Planting seeds with a folded envelop
4. COVER SEEDS WITH A THIN LAYER OF VERMICULITE
While this step is optional, I like to use vermiculite because it is light and helps retain the moisture in the growing medium. Vermiculite is a mineral that undergoes expansion when heated and forms light particles.
Vermiculite covering the seeds
5. LIGHTLY MIST THE GROWING MEDIUM
6. COVER THE PLANTING CONTAINER
Cover with either a dome or with plastic wrap to hold moisture during the germination process. Once the seeds germinate, remove the cover.
Cover planting container
CARING FOR SEEDLINGS
There are four primary things that seeds need: oxygen, moisture, light and a good growing medium. If you followed the steps above, then you already have a good start on the planting medium, oxygen (a function of the medium) and moisture. Let’s now look at the different stages of care:
1. GERMINATION
For the germination process, the seeds will continue to need moisture and should be checked each day. The plastic dome or plastic wrap will help keep the environment moist. Seeds also need warm soil temperature, and this can be aided by placing the seed tray in a warm place (65-75 degrees F) and/or on a specially designed seed heating mat (these are available in garden stores and online). I have found the heat mats to be especially helpful in speeding up germination. If you don’t have a heat mat, you can use the top of a refrigerator or a radiator. Once germination has occurred, the extra source of heat can be removed (e.g. heat mat, radiator).
Seedling heat mat to aid in germination.
2. SEEDLING GROWTH
Once germination has occurred; the dome or plastic wrap should be removed. The following requirements should be maintained. It is important to remember that the first set of leaves that develop are called the cotyledon or seed leaves (leaves that live within the seed, how fascinating). The second set of leaves are referred to as ‘true leaves’. You can see these in the picture of the spinach at the right.
In the image, you will see the cotyledon (seed leaves), which are the long slender leaves. You can also see the true leaves, which look more like a spinach leaf. These are the rounder, shorter leaves.
Cotyledon (seed leaves) and true leaves of spinach
Requirements to maintain
Light
The seed tray should be placed near a sunny window or under fluorescent/led lights. I use full spectrum led grow lights and have had good success. There are a lot of opinions about lights and I encourage you to read the following article from Texas AgriLife Extension Service. Without the right amount of light, the seedlings will become leggy and weak and may not develop their true leaves. I leave the lights on for 16 hours and off for 8 hours. It is important to give the seedlings a rest.
Water
Check your seedlings each day and water as needed. You can usually see, via visual examination, when the mixture is dry, and you can also feel the mixture. The smaller the size the of the container, the quicker it will dry out. I like using a cleaned dish detergent bottle for watering. This allows a very accurate watering process.
Fertilization
If the medium did not contain any added fertilizer, then you should fertilize after the seedling has emerged. This will ensure strong and rapid growth. I fertilize once a week using half the strength recommended on the fertilization container. Apply when you water.
Oscillating Fan
A fan is useful for promoting two positive effects: preventing disease and developing strong, sturdier seedlings. I run the fan on the same cycle as my lights (16 hours on, 8 hours off).
Thinning Out
If you planted your seedlings in individual containers and planted multiple seeds per container, then you may have multiple seeds germinate. To ensure that there is one strong seedling, it is necessary to remove the weaker of the seedlings. This is best accomplished by using a scissor and cutting the stem of the weaker seedling(s) right at the soil level.
Potting up
Some seedlings will need to be transplanted to larger containers prior to being transplanted into the garden. This is true if the seeds were broadcast into a planting container (e.g. each seed does not have an individual container) or the seedling grows too large for its initial container. Carefully dig up the seedlings and gently pull them apart. Handle the seedling by the leaves as opposed to the stems and roots. Place in the new container and water. If the medium used does not contain any fertilizer, then the seedling will need supplemental nutrients. Follow the same directions as mentioned above for fertilization.
Full spectrum grow light
Clean dish detergent bottle for seedling watering
Small clip on fan to strength seedlings after germination
When multiple seedlings emerge in a single cell, keep only one
3. HARDENING OFF
This is the process of acclimating the seedling to the outdoors. The timing of this process is based upon whether the seedling is a cold-season (lettuce, spinach) or warm-season plant (tomato, cucumber). Also, the seedlings should have multiple sets of true leaves before starting the hardening off process. New growth is a sign that the hardening off process is going well and the seedling is ready for transplanting (generally 1-2 weeks). There are a couple of methods to harden off plants.
Three Methods
- Place the seedlings outside for a few hours each day and bring back in at night. The temperatures should be relatively warm (55 degrees plus). At the end of two weeks, the seedlings should be ready to transplant.
- Place the seedlings under a cover (low tunnel) to create a greenhouse-like environment. Either plastic or specially designed row cover can be used (or a combination of both). Plastic row cover must be removed on sunny days to avoid excessive heat buildup. Plastic can be used to protect cold-hardy crops when temperatures are as low as 25 degrees Fahrenheit.
- Place the seedlings in a cold frame. A cold frame is like a mini-greenhouse. The advantage of the cold frame is that the seedlings can be left inside the frame with the vent being opened during the warmest part of the day. For cold-season plants, the temperature should not drop below 35 degrees Fahrenheit. For warm-season plants, wait until you are within two or three weeks from your last frost date.
Low tunnel
Cold Frame
4. TRANSPLANTING
The final step in the process. After the hardening off process, you are ready to transplant your seedlings in their final growing space. Take care to understand the spacing requirements between individual plants and between rows of plants (usually found on the seed packet). I find it helpful to first plan out the spacing, dig the holes and then plant the seedlings. In addition, it’s helpful to prepare the hole with a generous dose of fertilizer to give the transplant a good start. See fertilization above in seedling care.
There you have it. If you provide the seeds with a good growing medium, moisture, light and oxygen, and supplement that with care, then you should have good healthy seedlings. Remember approach your work with enthusiasm, enjoy!
Seed packet indicating plant spacing
RESOURCES
University of New Hampshire Cooperative Extension Seed Starting Fact Sheet
University of Connecticut Seed Starting Seed Starting Fact Sheet
Rutgers Cooperative Extension Seed Starting Fact Sheet
Utah State Cooperative Extension Seed Starting Fact Sheet
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