Every year, when spring comes we get always the same question. How to germinate seeds directly into the soil and what is the best type of soil for germination. Seeds are pretty stubborn and if you do not fail in one of the most common traps you can grow them very easily, even without soil.
To germinate seeds directly into the soil is necessary to 1) choose the right soil or medium 2) Choose and fill the container 3) Use a dome or cover 4) Water 5) Place the seeds 6) Wait and monitor. For successful soil germination, it is essential to guarantee stable moisture and temperature levels.
You just bought your seeds, and you are ready to plant them? Almost. Keep reading and you will have your highest ever seed germination rate. Let’s dive in!
Making seeds germinate directly into the soil is by far my favorite approach. The only secret for success is maintaining moisture and temperature level fairly constant through the whole germination process. How?
There are countless tricks and tools (DIY or that you can simply buy for a few dollars) to make your seeds germinate. However, for successful seed germination, the recommended steps are, in order:
- Choose the soil
- Choose the container and fill it with soil
- Use a dome (pro tip)
- Water the soil
- Place the seedlings at the right depth and distance
- Wait and monitor
1. Choose the Soil
The best soil for seedlings needs to be able to retain moisture to allow germination to start, be lightweight, and be porous for the first roots to develop. Moreover, being sterile is another great advantage that prevents the spread of bacteria or fungus that can harm the plant.
More precisely, you need to choose a seed starter soil that:
- Retain moisture: seeds tend to spend their first period just absorbing water. This with temperature is the “signal” for awaking and starts sprouting. At the same time, you do not want to water them too frequently to achieve this as you might risk waterlogged or displace the seed.
- Be light-weight and porous: the first roots are generally quite weak. Hence, in most cases, they will not be able to displace coarse or heavy soil. Shorter roots will imply a stunted growth;
- Be sterile: seeds are particularly susceptible to disease and fungi. If your soil already carries such diseases, then the chances for your seeds to make it might be quite low.
I used the light warrior from FoxFarm.
This seed starter mix has all of the mentioned above quality and even more. Indeed, it has very fine grain allowing the roots to easily penetrate the soil and maximize the surface area. However, it is not sterile. There are living organisms living there! Is this then bad?
Here the kick
The FoxFarm is enriched with a particular type of very beneficial fungi. Such fungi affect the roots creating small filaments attached to the plant’s roots. The crazy part is that these pseudo roots behave like real roots.
The plant provides sugar to these pseudo roots that, in return, give the plant (extra) water and nutrients. This has been proofed to boost development and plant growth.roo
Talking with other gardeners, they also had good success with the regular potting mix. In this case, you might want to go for a good one like the Fox Farm one.
Use a container that is at least 2-3 inches of depth. That will allow the seedling to develop some strong roots limiting the damage when moved to their final planter.
If you are using a DIY container, also remember to not fill the container totally until its border. Indeed, if you are using a dome, you do not want this to be in contact with the soil. This will prevent transpiration, and it will not leave space for the seedling to rise.
3. Use a Dome
Place a transparent plastic cover like half of a water bottle or a plastic film on the soil. This will allow to keep the soil moist and increate the changes of germination
Remember that the cover should not be flat on the soil as otherwise, the seeds will not be able to grow. If the soil level is below the rim of the container, then go ahead with a plastic film. However, if the soil level is the same as the container use a transparent plastic dome. Any will be fine, from a water or milk bottle. Be sure to clean it before as otherwise, it can smell due to the heat build-up.
4. Water The Soil To Boost Germination
The three best ways to water soil for seeds germination are:
- Bottom Watering: this can be done either before or after placing the seeds into the container. What you need to do is just to place the container (with drainage holes) on a saucer filled with water. If you have a seedling kit this comes with that needs to be filled with water where then the seedling cells are placed;
- Water the soil before placing the seeds: this will minimize the dispacement of the seeds. If you water after placing the seeds, the jet of water can displace them significnatly pushing them deep and preventing germination.
- Water the soil with a sprayer: in case you already placed the seed, just use a sprayer (with a gentle spray). Indeed, if you pour water into it, chances are that you are going to displace the seeds into the soil. Even worse, you can sink them down into the soil, preventing them from germinating.
The soil needs to be moist but not wet for optimal seeds germination. If you are unsure, just squeeze it a handful in your hands. If you see many droplets coming out, then it is way too wet.
I usually spray 2-3 times every cell with my sprayer. Remember, the majority of seeds are a millimeter in size.
Seeds should be placed into the soil at a depth of 2-3 times the seed size for ideal germination. They should be placed around 2 inches apart if the container is not the final one.
Dropping the seeds into the soil, right? Not exactly. The depth and distance at which you place them do matter (a lot).
Read the package. If it says 1-inch depth, then placing those seeds 1.5 inches below the surface will still be OK. However, placing them at 3 inches might significantly compromise their growth.
Check the table below with the recommended depth for seeds for the most common herbs.
|Seed Depth Recommended
|¼ inch (6mm)
|¼ inch (6mm)
|¼ inch (6mm)
|1/8 inch (3mm)
|1/10 inch (2.5mm)
|1/10 inch (2.5mm)
|½ inch (12mm)
|½ inch (12mm)
|¼ inch (6mm)
|¼ inch (6mm)
You can notice that all herbs’ seeds need to be planted very shallowly. We are talking about a fraction of an inch (just a few millimeters). Hence, making the mistake of planting them too deep is quite easy.
Two little hacks
To be sure that you are not exaggerating with the depth you have two solutions:
- You place the seeds on the surface (remember, 1 to 3 per cells or container) and then you sprinkle some fresh soil on top to create that layer you need;
- With the point of a pencil, you can create some holes where to place the seeds. This is what I do.
Place seeds on soil: another hack
Remember, the seeds you are going to grow are, very likely, being extremely tiny (just a few millimeters at most). This makes them slightly difficult to handle, especially if you have big fingers.
Hence, remember to dry your hands first. Otherwise, the moisture will make the seeds stick to your hands and fingers. Then drop the seeds on the palm of one hand and with the fingers of the other (or a pencil), you can drop them individually onto the soil. Believe me, this will make your life easier.
Do not confuse your seeds.
If you are using the seedling kit, you have the luxury of being able to start a massive amount of seeds at once. In these cases, chances are that you might plant different seeds in there. To avoid confusion, I would place some kind of label on them. You can also find some fun alternatives, especially if you do this with kids, like this one and similar on Amazon.
I do recommend placing the seeds of the same type in adjacent cells. Hence, for instance, if you’re planting 3 types of seeds, each type should use a third of the seedling kit.
6. Cover, Heat, Wait and Monitor
Once the seeds are in the soil, moist, and ready to germinate, you need to wait. In 1 to 3 weeks depending on the seeds, the first stem and pair of the leaf (fake leaves) will develop.
During the germination stage, I do not recommend watering the seeds (if you used the dome is not necessary). If you notice the soil is too dry then proceed with watering. Use a spray if possible so to avoid moving the seeds. You can use any of those available at home (after a deep cleaning if it was used for a chemical).
Temperature During Germination
To keep the temperature constant, the easiest solution is to place the seeds indoors, where the house temperature fluctuates less than the outdoor temperature. This should be easy especially if the seeds are in a small try.
However, if indoor is not an option then in this case you can use a heat mat.
- Place the heat mat (check section before) beneath the seedling kit or equivalent DIY solution you might have chosen. Remember that the mat should stay ON during the whole time until germination. If you have the germination kit, you also have the plastic dome’s advantage to trap the heat generated. Do not forget to open the small vents/holes, if present in the dome; OR
- If you do not have a mat, try to place the seedling starter kit or equivalent close to a source of light or (mild heat). If you have a plastic top cover (cling film) even better. If your house is not too cold, your seeds will still germinate. Check the germination time and temperature relationship.
If you followed all the previous, you should not have any problem. If you are using the seedling kit (with the bottom water tank), you do not need even water until sprouting!
The only thing I recommend is to check the dome and soil. Sometimes, especially in DIY solutions and lack of proper ventilation, green or white mold might appear—nothing to worry about as it is often inoffensive to plants. You can just open the lid and gently wipe them off (be careful not to take away the seeds).
Before starting, make sure to have ready all of the tools. Remember, everything listed here can be used multiple times, for countless seedlings. Hence, despite might be an investment of a few dollars, it made my life way easier. However, I will provide some free alternatives as well.
This is more important than it looks. Indeed, germinate seeds are quite sensitive to overwatering. Using a sprayer allows you to control way better the amount of water you need to provide. Another significant advantage is the ability to spread water uniformly across the soil surrounding the seedling without moving it.
A sprayer is always useful. It can also be used to spray away pesky aphids (strong spray) or to provide some mist to indoor rosemary. Do not forget that it can also be used at home to make your kitchen surface shiny and fragrant with a homemade herb-based cleaner. A good sprayer is definitely a good investment, and it lasts several years.
If you do not have a regular spray bottle that you can recycle from some of your house products, that can be a good idea.
Remember, if you use something that you found at home, wash it thoroughly and, after that, leave it full of water overnight to give it a final wash. You do not want to add some nasty chemicals to the water you provide to the seeds.
When you choose a container, remember to not use a regular planter. I made this mistake a couple of times and ended up killing half of the seedlings during transplant (they get untangled).
Moreover, I did not provide them with enough moisture (just too much soil compared to the size of the seedlings). Do not get me wrong, it can still work, but it is a hassle to take care of and transplanting.
When choosing a container, two things are important:
- Having little compartments: each compartment is destined to grow one or a few (no more than 3) seeds. Why is this important? Because it will allow you, in later stages, to easily transplant the grown seedlings to their final pot as their roots will not get tangled with each other. Moreover, you can grow more seedlings in a little space (and less soil)
- Having a moist retaining system: this can be as simple as a plastic cover. Why? Seedlings need moisture through their development (germination time might vary from a few days to weeks, depending on the herb you are growing and temperature).
During the years, I used several systems, especially when I experimented at home with the packaging of scrap products (on this more later). However, over the years, I opted for the more reliable seedling kits.
The one I used recently, here to check its current price on Amazon, and honestly is pretty good. Indeed, it has several qualities at once.
Having a good seeds starter kit can solve many (if not all) germination issues.
- Numerous seeds: Such seedling kits have dozens of separate cell-seedings allowing you to grow a large amount of seedling at once to counteract the potentially low germination rate. Do not also forget the advantage of having lots of plants to enjoy. Such cells have the right size for the small seedling to grow for 1-2 weeks Do not place more than 3 seedlings per cell;
- Stronger roots: the seedlings’ cells are deep. This allows your seedlings to germinate and develop a decently strong root system. Indeed, the majority of herbs and plants tend to develop vertical roots. So having space for their growth to give a head start to your herbs is a must;
- Constraint moist: such kits are equipped with drainage holes at the bottom. More than drainage holes, this works in reverse. They allow the water in the tank beneath it (on this more later) to be sucked by the soil when needed. So, the seedlings will always be moist but not waterlogged;
- Not much attention: due to a combination of the water-filled tank and plastic dome, the required condition of temperature and moisture are easily maintained over the time needed for your seeds to sprout. This, in turn, will require less time from your side.
As always, having the right tools matter to make your life easier, but none prevents you from having similar results for free.
For instance, you can replace the germination kits with many other DIY solutions. I tried many of them (although the sky is really the limit here), and most of them are OK (ish). They are free, but they require more of your time to allow your seeds to germinate here.
I love brownies, and often they are sold in shallow plastic containers with a movable dome. Another alternative might be the mushroom plastic boxes. In this case, they do not come with a cover (some cling film will do the trick).
This is an OK replacement for several reasons. They are transparent for you to see the seedlings growing, they can be (almost) closed to keep moisture. However, they do not have any drainage holes (you need to do them yourself).
Also, seedlings can easily get tangled if you do not place them far apart (I recommend 2 inches) within the box. This reduces the number of seedlings per surface area. Moreover, you might need to use way more soil compared to a proper seedling kit
Any small plastic bottle (those of up to 500ml, the smaller, the better) can be cut into two parts. You can use your kitchen scissors, especially for the thin plastic of the most common water bottles.
You can then fill the lower half (that should be around 3 inches tall) with the chosen soil. Do not throw away the upper part yet, it can be useful for later. Remember, if you go with this solution, place just one to three seeds per bottle. Also, remember to pierce the bottom to guarantee adequate drainage.
This is what everyone around recommends. I tried both the cardboard and the plastic version. They are good solutions, but they require a bit more attention compared to a seedling kit.
If you can, choose the plastic egg containers for your DIY seed starters. However, you need to create at least one drainage hole per egg cell. For this purpose, just warm up with a flame any piece of metal you do need and pierce the plastic (be careful here). If you do not have drainage holes, given the small size of the egg cell, the soil in it will likely end up soggy soil (as the water will stagnate at the bottom).
Paper cardboard egg containers are better for seedling watering. The water is partially absorbed by the cardboard rather than stagnate at the bottom if you do not have drainage holes. The problem here is the lack of a dome to trap the moisture and keep the temperature constant.
The problem I encounter in general is the small size of the cells. Indeed, they can barely contain 2-3 teaspoons of soil each. This means that your seedling will sprout, but it will not have enough soil to develop a good root system and get strong enough to be easily transplanted in a larger pot. It can still be done, but you need to pay extra attention when you transplant the juvenile seed (very fragile) to a new pot.
What about a normal planter (or perhaps an improvised cut in half milk bottle). Does not work well as a seedling starter? Again, as in the previous cases, it can work but requires a bit more attention.
Avoid these mistakes:
- Planting more than 1 (to 3) seeds: if you do so as it will get challenging to remove the seedling once grown, especially if your pot is overcrowded. I made such a mistake as well. Just plant 1 to 3 in the center, and then, once they grow, you can either try to save all of them or just cut the less fit and leave the strongest one.
- No watering enough: Another problem here is the lack of moisture control and the excessive amount of soil. The first problem can be solved with a simple clinging film on top of the container. The other one is the excessive amount of soil compared with the tiny seed. Indeed, it might be very easy to not water enough as the water you apply tends to spread and go down through the pot far away from the seed(s).
Source of Heat For Seed Germination in Soil
If you have ever grown seeds, you know that one of the critical aspects of their successful germination is the temperature. As detailed in this germination temperature and timing guide, seeds grow only within a certain temperature range. At the ideal temperature, they grow even faster and stronger.
Again you have two solutions, the heating map or some DIY solution.
A heating map for seedling is a very thin and flexible miniaturized heater placed beneath the seedling kit (or DIY alternative). Such a map reaches and maintains the ideal temperature for your seedling. The heat is transmitted to the bottom of the seedling kit (often plastic) through the soil and then the seeds.
Such a mat typically needs to stay in operation (plugged to your electric socket) during the whole germination period (a few days). However, do not worry, it consumes like a small light bulb, so nothing to worry about for your electricity consumption.
If you are lucky to live in a sunny region, place the seeds (when still beneath the soil) close to a sunny window. The light will warm up the soil.
Again, if you are careful enough, and your seedlings are equipped with a dome in front of a sunny window, you will be able to provide them with the needed heat. Another approach is to place them close to a lamp for a few days.
Before having a mat, I used to place the seeds inside the room containing the water tank boiler (the tank where the water of your house is warmed up). That room always ended up being warmer than the others.
A dome is any type of heat and moisture-retaining cover. Any piece of transparent plastic will do the job. Despite its simplicity, this is quite an important part of growing seedlings. Again, I managed to grow seeds (especially easy ones like basil) without it, but using it will make your life much easier. Indeed, by trapping the air creates a more controlled and stable temperature and moisture environment.
If you use any seedling kit, this plastic dome comes with it. It might also have some small ventilation vents. This is quite good to have as it will allow the air to circulate, preventing the formation of fungi, bugs, and mold.
In this case, just using a cling film on top of the container will suffice. Remember, do not tightly close it. Why? Because that will not allow the air to circulate. Just leave the border slightly open. Not the best circulation, but it should still be OK. If all goes well, your seeds will sprout in a few days.
A little hack
To create the dome of your DIY germination kits, you can use some transparent plastic bottles (any bottle of 500ml or less will do the trick). Just cut them in half and stick the upper half (the one with the lid) into the soil. Take out the lid creating a mini greenhouse. This works really well if you decided to plant the seeds in a pot.
- To germinate seed in the soil a light-weight, sterile and porous soil is the best;
- Seedling kits are the easiest option to grow seeds. They can be reused many times and have very low maintenance. Plant and forget.
- There are many DIY hacks if you want to experiment, from egg containers (plastic with holes) to dome done with plastic bottles or cling film.
Can potting mix be used to start the seeds? The potting mix is a valuable alternative to start seeds. However, it is important to make sure that the potting mix is fertilizer poor to avoid root burn. The germination rate might be lower due to the coarser nature of the potting mix.
Will seeds planted too deep germinate? In case seeds are planted much deeper than recommended, they might die after sprouting. This because they will not have enough energy to produce the long stem needed to reach the light.
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