Different Types of Seeds
Seeds come in many different shapes and sizes that all serve their own purposes Some seeds, like the coco-de mer, are extremely large and can weigh up to 40 pounds. This seed floats through the ocean (mainly the Indian Ocean) in order to travel between islands. Certain epiphytic orchid seeds are 1/300th of an inch in size and travel through the air like dust. Epiphytic means they absorb nutrients and water from the air rather than the soil. They attach to other plants. Alternatively, some other seeds like dandelion or milkweed are larger but have wings or feathers that catch the wind and they travel through the air. Other seeds are encased in a delicious fruit that is eaten and travels via animal that way or burdock seeds which get caught in animal fur (or on human clothes) and travel that way. All of these seeds have different size or shape traits that attribute to what?
DISPERSAL - The way they move around in their environment
Most of the seeds we grow are angiosperms. Angiosperms are defined as plants that have flowers that produce seed encased in a fruit or carpel (part of the reproductive system). The seed is the embryonic stage of the plant life cycle. It’s the very beginning of life. Most seeds contain three parts- the embryo, the endosperm, and the seed coat. The embryo is the fertilized part of the seed. The part that will become a plant. They will have one or more embryonic leaves known as cotyledons within the seed. The endosperm is made up of starches, oils, and proteins and is the food source of the embryo in early life. The seed coat is the protective outer layer of the seed.
Some phrases you might come across when searching for seeds are open- pollinated and hybrid. Open Pollinated seeds are seeds, which if properly isolated from other varieties in the same species, will produce seed that is genetically “true to type.” This means that when the seed is saved and replanted the next year, you will end up with the same traits as the parent plant had. When you're shopping with us, you're always getting open-pollinated seeds. In this same vein, heirloom seeds are open-pollinated varieties that have been being saved for over 50 years. If open-pollinated varieties are allowed to cross (Fordhook Giant Swiss Chard and Flamingo Swiss Chard for instance) they will create a hybrid seed which is a mix of both varieties. In modern hybrid seed production, this is a deliberate and meticulous process to produce one or more particular traits. This seed can be saved but will not be true to type. The results will be unpredictable.
Seed saving is a huge benefit to using open-pollinated seeds.
Open-Pollinated seeds tend to be less expensive than hybrid seeds.
The flavor of open-pollinated seed is unrivaled and the reasons they have been saved for so long are because they are beloved.
Hybrid breeders tend to focus on traits such as storage ability, uniformity, size, etc.
These seeds also tend to be more disease resistant because it is easier to select for this trait in hybrid seeds than established open-pollinated varieties.
“Hybrid Vigor” describes the increase in overall vitality of the offspring of two different genetic lines. This isn’t necessarily incredibly obvious in all varieties but in those that it is, it can be quite significant resulting in higher yields and faster growth.
Reading Seed Packets
Seed packets can have slightly varying information on them but in general, they’ll give you a brief description of the variety and some planting information.
- Seed Spacing - This refers to the distance between the seeds when you’re direct seeding. Certain packets that require you to start the seed in trays will not have this information. Peppers and tomatoes for example, will not do well if direct seeded into the ground. If they’re started directly during the right time of year they will not have time to mature. Some other seeds you might want to start inside will have direct seeding information because they can be direct seeded.
- Seed Depth - This information refers to the depth with which you should plant in the soil, either directly or in trays. In general, seed depth is dependent on the size of the seed. Larger seeds such as pumpkins are planted deeper than smaller seeds like those of kale or collards.
- Days to Sprout - This refers to the expected days from seeding to germination. Sometimes these time frames can be a wide range of time (such as peppers, which can be 8-25 days). The speed of germination is dependent on the conditions in which the seed is planted. Cooler weather may result in slower germination for certain seeds. Moisture levels can also affect germination. If your seeds do not germinate within this time frame it’s time to reevaluate the conditions in which the seed is in and re-seed.
- Mature Spacing - This refers to the spacing that is necessary between the full grown plants in order for them to grow efficiently. Why is the seeding space and mature spacing so different? Arianna lettuce, for instance, is a lovely bolt resistant head lettuce. On the seed packet, the seed spacing is ½ inch and the mature spacing is 6-10 inches. The reason you would seed closer together is to ensure an adequate germination. If you give many seeds an opportunity to grow you’ll end up with the correct amount of lettuce you want or need in the end! If you only plant seeds 6-10 inches apart and some of the seeds are lost to birds or rot, so on and so forth, you’ll end up with far less lettuce than you want.
This direct seed method requires “thinning” which is the process of pulling out plants to create a mature distance of 6-10 inches (in the case of this lettuce), discussed above. For transplanted plants this can also be the transplanting distance.
- Days to Harvest - This phrase is in regards to the time from planting to harvest, not from germination. In other words, the seeding date to maturity. Sometimes you can get starts that will say Days to Harvest and that will be from transplanting day to harvest, excluding the germination time.
- Latin names - All of our seeds have latin names on the packet. What you’ll notice is, if you’re looking at a certain vegetable, all the varieties we offer have the same latin name. Most of the peppers are Capsicum annum, all of the melons are Cucumis melo, and all of the lettuces are Lactuca sativa, so on and so forth. All of these different vegetables are of the same species but different varieties. This is important for one main reason: Seed Saving
- Sell by Dates - Let me make the distinction between a “Sell By” date and a “Use By” date. Seed companies are required to share a Sell By date due to very technical food regulations. This sell by date is one year after the seed is packed. The truth of this is that seeds are good and viable for several, in some cases, many years, dependent on the methods with which they are stored and cared for.
Seed packets sitting out in a bright window for several years will have declining viability over the course of that time. Seeds that are stored in an airtight container in the refrigerator will stay viable for much longer.
- LOT Numbers - LOT Numbers are another thing you’ll see on seed packets. This refers to the several pounds of seeds that we get into the warehouse and then pack to sell. LOT numbers help us to track where our seeds are going so when there’s an issue with a seed we track it back to the LOT and see if we have had any other issues. We can have a LOT in stock for several years so it’s cool to track them over that time.
- Approximate Seeds - For our seeds, we pack by weight. And so every time we get a new variety, we count out how many seeds are in the appropriate weight so we can update the label. This is approximate because seed size can vary slightly depending on the LOT.
A Note on Germination Rates:
We get our seeds tested every six months to see what percentage they’re germinating at. We do this to make sure that every seed we sell meets Federal Germination Rates. The government has a list of appropriate rates in which seeds can germinate at in order to be legal to sell! We follow these! LOT numbers are very important to track this data as well.
What a Seed Needs
As we mentioned before, the seed coat is the protective outer layer of the seed. Breaking the seed coat is necessary on all plants. But it doesn’t take extra steps with all plants. Seed coats break in conditions dependent on the type of plant. For instance, many vegetable seeds just need a little air and moisture. Other seeds require more or varying steps. In nature, this allows the seed to germinate in the best possible conditions to ensure seed and seedling survival.
This method is necessary for seeds with internal dormancy that is regulated by the inner seed tissues. This dormancy prevents seeds of many species from germinating when environmental factors are not just right for seed survival! Cold treatment is necessary for plants or trees that require time in the ground over winter in order to germinate. This can be done by planting in Autumn or early Spring but can sometimes result in spotty germination (seeds may be lost or eaten). Alternatively, you can create a “false winter” to trick the plants into germinating. About three months before spring, place seeds in a plastic bag with a handful of slightly dampened peat or coco coir. A paper towel can work too. Seal and label the bag with the seed name and date and store in the refrigerator (not the freezer) for 6-10 weeks depending on the plant. Be sure to keep the coco coir or paper towel slightly damp during the duration of treatment. After treatment, your seed is ready to plant. Practice stratification with plants like echinacea and milkweed!
Seed coats that require scarification are impervious to water and gasses. The seed cannot germinate until the coat is physically altered. Any process of breaking or scratching the seed coat is known as scarification. In nature, this can happen during freezing temperature, microbial activity, or the passing through of an animal's digestive tract. To create this system at home, seed coats can be filed with a metal file or sandpaper, nicked with a knife, or cracked gently with a hammer.
Water scarification is another useful method. Bring water to a boil, remove the pot from the stove and place the seeds in the water. Allow the seeds to soak until the water cools to room temperature and then sow. Seeds should be dull in appearance but should not be deeply pitted or cracked as this would result in a damaged embryo, inhibiting germination. Keep in mind that scarified seeds do not store well. Nasturtiums can benefit from this process.
Seeding Indoor or Outdoors?
There are certain seeds that will do better if started indoors and certain seeds that are grown better when direct seeded outside. In general, most root crops such as carrots, parsnips, burdock, and radishes are better off direct seeded. Fast growing plants such as cut and come again lettuce is also better off direct seeded. Direct seeding helps avoid transplant shock or root disturbance which is important for root crops. In general, larger and slower growing plants do well when started indoors. When we do this we are able to have harvests earlier and for more of the growing season.
Sowing Cucurbits like cucumbers, squash, and pumpkins indoors can be helpful earlier in the season but they are prone to transplant shock so you may consider direct seeding and see what works better for you! Another thing to consider is the kind of space you have. If you don't have a ton of space to start seeds indoors, prioritize what cannot be direct seeded.
Many herbs that can take multiple weeks to germinate are good to start inside for harvesting reasons and germination rates.
Beans and Peas should be started outdoors as they do not transplant well.
Root crops as previously mentioned
Onions can go either way.
Garlic is also planted directly outside.
For direct seeded plants, be prepared to “thin” your seedlings to the correct spacing for the plant. Plants that are too close together compete for light and nutrients and get stunted and lack of airflow encourages disease. You’ll want to do this once the seedlings have two true leaves, so the leaves that grow after the cotyledons. Transplants can sometimes be more resistant to insect and other pest pressure because they are larger and more established once they are moved into the garden. Be prepared to harden off your transplants before you put them in the ground outside. This involves putting them outside for a few hours each day, increasing the times, for about a week before you’re planning on transplanting.
Starting Seeds Indoors
When a seed comes into contact with moisture (ideally in the perfect soil/air/moisture situation), the seed begins to take up water through the seed coat. This causes the seed to swell which then breaks the seed coat from the inside. The embryo is made up of a small shoot and a small root. The root emerges first, anchoring the seed to the soil. As it grows it takes up the job of absorbing moisture. Once this happens, the shoot emerges. We’ve discussed how seeds will “wake up” and germinate once the conditions are favorable for them. And how different seeds may need different conditions in order to germinate. This is true even for seeds which do not require stratification or scarification. All seeds need the proper temperature, moisture, air, and light conditions in order to germinate.
All seeds have optimal temperature ranges in which they will germinate. This information is not often found on seed packets but is easy to find or even infer! Nightshades and Cucurbits (think tomatoes and cucumbers) are high summer crops so they germinate best with higher heat! In this case, tomatoes germinate best with soil temperatures between 70 and 90 degrees, whereas cucumbers can be started in slight cooler soil at about 60 to 90 degrees. Peas and spinach are cooler weather crops and can germinate starting at about 45 degrees going up to about 70.
“Seed to Soil Contact'' is a phrase you’ll likely hear a lot of; fine-textured soil with little compaction is ideal for starting seeds either in the field or in trays. Dry, rocky, light brown colored soil will not do the trick. Think dark, moist, and fluffy. The contact is important so that the seed is able to suck in enough moisture from the soil in order to germinate. If the soil is too wet it will be heavy and compacted and suffocate the seed, literally, there will be no air pockets. Seeds also need that air to complete its processes.
We like to think about the growing season as a cycle. Starting in February or March (usually) you’re thinking about cool weather crops such as kale, cabbage, lettuce, etc. As the weather warms up you’re thinking about cucumbers and tomatoes and summer squash. The season ebbs a bit and those summer crops start looking worse and worse so you begin thinking about the cool weather crops again and it just cycles all over. It’s a good idea to start most seeds indoors 4-6 weeks before you’re ready to plant. There are some exceptions to this rule- such as tomatoes and peppers which you’d want to start inside as early as February (March at the latest) even though they wouldn’t go into the ground until after Mother’s Day.
Creating a Seed Starting Mix
There are one million different ways you can design a seed starting mix (or just purchase one if you’re so inclined). Some folks recommend a soil-less seed starting mix which would be using peat moss or coco coir as a base. You can also use compost as a base. And then you’re looking for an aeration agent, most likely perlite. The bottom line is that you want a fine, fluffy seedling mix that will be high in nutrients. Potting soil can be used but they tend to have a coarser texture which can mess up your seed to soil contact needs. These potting soils can sometimes have manure based compost which can be especially high in nitrogen which is a bit too intense for seeds, causing them to “burn” and inhibit growth. These potting mixes can also often contain field soil which can carry diseases.
Sterile seed starting mixes is what you’re looking for. When you’re buying potting mix, you’ll often see the word sterile on the packaging. This means that the soil/mix has been heated past the point of survival for many bacterias and harmful pathogens, which can harm or inhibit the growth of your seedlings.
A Note on Peat Moss:
Peat moss is very popular and commonly found in seed starting mixes. It is found and grows in wetlands and bogs and taken directly from these places and packaged. This process severely upsets those ecosystems. On top of that, peat lands around the world store a third of the world's soil carbon so harvesting it releases that carbon, directly contributing to global warming. And to me, there’s just something about trying to practice a regenerative form of gardening/agriculture that also contributes to this particular vicious cycle. And so these days I just avoid peat moss and have switched to coco coir instead! Coco coir is made from the husks of coconuts and works beautifully.
Example seed starting mix recipe:
Compost and/or worm castings make a beautiful base because it gives your seedlings that necessary nutrient boost while still being gentle (this gentleness comes particularly with the worm castings). The coco coir protects from burning the seedlings if your compost is a little too “hot” by cutting it in half. Coco coir retains moisture really well and adds that fluffy texture. Perlite lightens the mix and helps with aeration so the plants can get oxygen. If you’ve ever seen a soil mix, perlite are the little white bits that look like styrofoam. This material is not styrofoam and is actually naturally occurring and made out of volcanic glass! This is a really basic seed starting recipe and you can amend it with different additives for what you need! Kelp meal for instance is a low NPK fertilizer (around 1-0-2) that acts as a growth stimulant and supports germination and root development. Azomite is another amendment you might use as a seed inoculant (coating the seeds in it before planting) that helps with germination and initial growth by providing over 70 trace minerals and elements that may not be present in your mix.
Tools for Starting Seeds
Heat mats have one main purpose which is to gently warm the soil and maintain that heat to create a good environment for germination. This is more necessary with certain seeds than others. Like we discussed earlier, seeds have different optimum temperature ranges in which they will germinate. If you’re trying to start seeds such as peppers and tomatoes in February, you likely will not be able to get them to their optimum temperature range of 70-90 degrees without assistance. This is where the heat mats come in. Heat mats sit under a seed tray or pot. Some of them even have a thermostat so that you can adjust the temperature. Soil should be checked daily (as least) because using heat mats also quickens the drying out of the soil. You’ll need to water them more consistently and/or keep a closer eye on them. It is generally recommended to remove seedlings from the mat once they have germinated. If the room they’re in is still cool you could also keep them on the mat but create a few inches of airflow in between the mat and the tray. Too much heat can result in leggy seedlings but too little won’t work for them either.
The good grow lights are expensive and the affordable ones don’t always do their job. Frustrating. But, we also know that plants require light for photosynthesis. Naturally, if we’re starting seedlings indoors, they’re going to need light. Oftentimes, placing our seedlings near a window does not provide enough light. Plants that are not getting enough light can often be a pale green to yellow color (as they’re not able to produce enough chlorophyll) and can have long, thin stems attributed to “legginess”. This happens when plants are trying to grow towards a light source so you’ll often see them all bending the same way (usually towards a window). Adding artificial light can solve these problems for many plants. The most common types of lighting are LED and Fluorescent bulbs.
Super energy efficient
Last a long time
Wide spectrum of light (which is a marketing term meaning your light closely resembles that of the sun)
Do not overheat
Moderately energy efficient
Cheaper upfront costs
Typically have a less wide spectrum of light but some bulbs are more than others.
Higher upfront costs
Do not last as long as LED’s
Use more energy than LED’s
We’re talking specifically about agricultural plant starts here but you can also get grow lights for certain house plants which may emit different light. For instance, flowering houseplants do really well with red light. Talking about which grow lights are best for you so on and so forth could be a whole other class. In general though, bulbs with a Correlated Color Temperature rating of 6500 Kelvins are closest to natural light. And we’ll stop with the color spectrum there :)
You also want your light source to be evenly distributed. This is why you’ll often see grow lights in tray form, LED’s spread out over a surface that hangs on top of your seedling tray. The other thing to note here is that you’ll want to purchase adjustable light fixtures so that you can raise or lower your lights as your plants grow or you start more seeds. Generally you want your lights to be 4-6 inches above your tray or plants, whatever height they’re at. The last thing to consider is light duration. Seedlings generally need 16-18 hours of light per day. You’ll want to connect a timer to your grow lights to ensure this!
We’ve talked a lot about the importance of moisture in regards to germination and seedling development. But how do you know if it’s right? Everyone says you want your soil to be moist but not wet, and I don’t find this information very helpful to be honest. You’re looking to have about 40-60% moisture in your trays at any given time. This can be a difficult thing to calculate. But if you can imagine a handful of soil- when you squeeze it, water should not seep out between your fingers. But when you open your hand, the soil ball should stay intact and not crumble on your palm. This is the moisture level you’re looking for. Of course, once your seedlings are in trays it can be hard to execute this particular test. That’s why it’s a good idea to water your seed starting mix to this level, fill your trays, and keep them watered from there. That way you can create a consistently moist environment for your seeds. Once you start with moist soil, you can expect to need to water your trays once a day. If you’re using a heating mat you can add an additional watering with a spray bottle per day. A heavy mist should do the trick but use your eyeballs! Soil should be fluffy and dark, not cracked or crumbly. Once seeds germinate, their water needs drop dramatically.
NOT GIVING YOUR SEEDS ENOUGH WATER IS THE MOST COMMON MISTAKE THAT NEW SEED GROWERS MAKE - Don’t let this be you!!
We mentioned earlier that lack of airflow encourages disease. This is true with full grown field plants as well as seedlings! When there isn’t enough airflow in a garden inside or out, the air and area can remain damp for extended periods of time. This dampness creates the perfect home for a host of fungal diseases. Which can wreak even more havoc on young plant starts. The ability to have a window open (during the day if it’s not too cold) can make all the difference for indoor plants. Having a fan running will help too! Either a ceiling fan or oscillating. It does not need to be blowing on the plants but simply running in the room.
You can start seeds in many different types of pots. Always feel free to use whatever you have on hand! Old houseplant pots (as long as they’ve been thoroughly cleaned), cans, plastic bottles, egg cartons, the list goes on! We just want to touch on briefly- the use of seed trays. The most common seed trays you’ll come across are “50’s” and “72’s” and these numbers get higher and lower and simply refer to the number of cells in a tray. The higher the number, the smaller the cells, which means the more plants you can start but also the less time that the plant can spend in the cell without becoming root bound. If you choose to use trays, keep in mind what time of year you’re starting seeds and how long they’ll have to spend in the pots! If you’re starting Brassicas in 50’s in February, they probably will not have to be potted up. On the other hand, the tomatoes you’re starting in February will need to be put in a larger pot at some point between now and May when they go in the ground! So it might be worth considering planting these in larger containers. Reusable six celled trays are great for home gardeners looking to maximize space and efficiency!
Common Seedling Issues
“Damping Off” is a term used to describe a symptom of many different fungal issues that all result in the same thing- seedling death. It is when the stems of your seedlings start to get thin at the bottom and turn brown, eventually killing the seedling. This mostly happens when seeds are planted and kept in cold, overly wet soil. These issues are further exacerbated by compost overly high in Nitrogen, using non-sterile seedling mix, or lack of air circulation. Once this occurs, there’s no saving them so think about prevention first! Planting with a little sprinkle of cinnamon may help.
Another fairly common occurrence is a gardener purchasing seedlings from a grower or nursery and bringing home pests or diseases with them. Aphids, cabbage moths, and spider mites can all hide inconspicuously on a seedling and will find, once it’s home with your other plants, that it’s been dropped into plant-destroying-bug heaven. It is really important to check your seedlings closely before bringing them home, looking under the leaves and checking for bugs but also eggs. You can also spray a light layer of Neem Oil on plant starts before your introduce them to the rest of your plants.
Check out our collections of seed starting supplies and early spring crops!
Article Written by: Hannah Gibbons
About the Author: Hannah Gibbons, an employee at Sow True Seed since 2020, has nearly a decade of experience in the agricultural industry. Their passion for environmental education and regenerative agriculture has been the cornerstone of their work, aimed at making gardening accessible to all.