Seed Germination Techniques
See our table below for the species you are trying to grow for guidance on germination techniques.
1 Pre-treatment of seeds prior to sowing
1.1 Orthodox Seeds - Dried Seeds
This group of seeds are technically considered seeds that are able to withstand drying and/or freezing. There are also "intermediate" seeds which tolerate varying levels of drying, freezing or long term storage.
1.1.1 Direct Sowing
Some seeds are relatively easy to grow without any pretreatment and thus can just be sowed directly into the appropriate growing medium with relative success. Care should be taken, especially in field applications, that the right humidity, light levels, humidity, weed management and protections from pests & diseases is assured.
Some seeds germinate slowly on their own due to their seed coat being difficult for water to penetrate and begin the germination cycle. Naturally, some seeds require help to “break” the seed coat. Forest fire, animals digestive system, washing around on sand etc. There are some common techniques that may work in a similar way to natural methods that will scary the seed coat.
Hot Water: Many seeds with hard coats, especially many members of the Fabaceae family, do well with a boiling water soak or a hot water soak. This method is not intended to actually boil the seeds, which may more appropriately just be called cooking them. It is more just to damage the seed coat. Bring some water to a boil, place the water into a container such as a cup of bowl, place the seeds into the hot water and let soak for 6-24 hours depending on the species. Generally speaking, species that require this technique plus water soaking can be sowed once the seed begins to swell. Sometimes if the seeds are left too long the seeds will appear to explode and become unviable.
Sand Paper: Some seeds just need water to penetrate the seed coat, and sand paper is a common trick to break the seed coat’s outer surface to allow water to penetrate the seed. Other things such as knives, files and scissors are used as well, but sand paper is far safer for the majority of people. Generally speaking, this is a slow method left for particularly difficult species or when not many seeds are needing treatment.
Acid Bath: Some seeds are scarified using an acid, simulating that of an animals digestive system. This is simply often just a water soak modified by the PH of the water. This generally involves using acidic chemicals and proper safety precautions should be taken, especially with more dangerous acids such as HCL.
Some seeds require more than the moisture in the soil to trigger germination. Soaking the seeds in water is quite effective for many species of plants. Some species may need scarification first which will open the tough seed coat to allow the water to penetrate the seed coat and begin the process.
Sometimes seeds can also be grown in a manner between soaking and direct sowing. Using moist paper towel with seeds placed inside is a common method to "soak" the seeds without placing in water which can achieve an in between of more air than water and less chance of rot in soils.
1.1.4 Cold Stratification
Some species require a winter before they will germinate. Usually these species are from temperate regions. Often times a period of cold will suffice. We use the refrigerator to achieve this. Some species are done dry, others like maple can be done wet with a mix of sphagnum moss or vermiculite and placed in the fridge for a couple months. This method is intended to give the seeds a proper dormancy which is induced at certain temperatures and requires varying lengths of time depending on the species.
1.2 Recalcitrant Seeds - Fresh Seeds
Recalcitrant seeds, A.K.A. unorthodox seeds, are seeds that must stay fresh and generally cannot withstand super cold temps or drying out. Many tropical plants fall into this category, but certainly not all.
Most recalcitrant seeds do not require any special pretreatments for germination. Some species with hard seed coats may require scarification or a soak. Some species particularly prone o pathogen attacks may be treated with anti-fungal and similar products to reduce the risk of rot.
2 Growing Media (Soils)
2.1 Inorganic Media
2.1.1 Sand, Grit and Rock
Rock based: media is generally used when either hydroponic application is desired or pathogen attack, such as fungal, is a risk. Inorganic media tends not to cause problems with bacteria and fungus due to a lack of nutritional available. Nutrients will need to be added once the seeds germinate and start growing, or the seeds can be transplanted to a different growing media.
The main things to consider with rock based mixes are size in relation to air flow. Moisture containing properties. Things like pumice are used to aerate the soil and does not tend to retain moisture. Vermiculite on the other hand can aerate and hold a fair amount of moisture.
Expanded clay, often found in bonsai and aquaria related stores, is much like rock in size but becomes softer and can retain moisture. We use it a lot for taking cuttings, but sometimes can be useful in seed germinating mixes of some species.
Clay is essentially very fine rock dust, or silt, and tends to have good moisture retaining qualities and very poor air flow qualities. We find this ingredient not so useful in germinating seeds but useful in growing up plants when blended with other amendments.
2.2 Organic Media
2.2.1 Sphagnum Moss
With most unorthodox seeds we grow, we tend to use either sphagnum moss or vermiculite as a media to let them start germinating in a clean environment. The media is soaked thoroughly then squeezed by hand to take out excess moisture. The seeds, which should be clean of all pulp and other debris in order to avoid mold, are placed into the media in a plastic bag to avoid dehydration or a covered tray. Airflow is essential for pathogen prevention. When the seeds sprout they may be planted into their desired growing medium. Also read our article: Germination Techniques for Tropical Recalcitrant Seeds and How to germinate Durio species seeds
2.2.2 Peat and Coco Coir
Although the sources are different; bogs vs coconut by product. But the structure, air flow and water retaining qualities are fairly similar and thus can be used in much the same manner. Coco tends to have slightly more fungal issues, while peat long term tends to get acidic and harder. Coco is also clearly the more environmentally friendly product as it is a by-product of the food industry rather than dredging up bogs.
Coco coir and peat moss are quite useful as an amendment or a base in custom soil mixes. They work well to loosen up heavy soils and also bind together loose hard ingredients. They have good water retention and are useful for more acidic soil types.
Not often really useful for the direct germination of seeds, but useful very quickly for nutrition once the seeds have sprouted roots. We add it to mixes that will be used to grow seedlings up a bit larger as its filled with nutrition and has great structure.
Due to pathogens and sometimes the ability of them to attacks seeds, we try to avoid compost for germinating seeds, though can be great for seedlings. By its very nature, compost is very much a living media filled with billions of microorganisms. It is great to use as a transplant or with seeds that are hardier against such organisms. For some species, it may even be essential to proper plant health due to the mycorrhizal cooperation they make with the roots.
2.2.5 Seedling mixes
There are many commercially available bagged soils that are used to germinate seeds. Generally, these soils are devoid of large organic debris, which will greatly reduce fungal and bacterial problems with the seeds. These tend to be of a consistent grade and moisture holding capacity and thus makes things more reliable. Usually these bagged products are advertised as sterile, if that is needed for your application be sure to smell the bag when opened for any musty fungus type odors and avoid its use if noticed.
3. Environmental Factors
Many species require a certain temperature to germinate. Some species are sensitive to cold, while others the heat. Most seeds fall into the 15-25 degree range, but check the species for best results. Some species may also need cold stratification in which they benefit from a winter period prior to germinating. Maple and ginseng are well known examples of species that benefit from a cold period prior to germinating.
In general you want the soil to be moist and not wet. if you hold the wet soil in your hand and squeeze as hard as possible to let out the excess water, the remaining soil when loosened is often about right for many species. Water logged soils tend to be anaerobic and provide ideal conditions for bacteria which tend to harm seeds.
Humidity is species specific, humidity is often required for small seedlings to avoid dehydration while the roots develop. Interestingly even many cactus species when germinating tend to start and do well in relatively moist conditions.
Some species require light to germinate, others require darkness while others don't seem affected either way. Many times species that require light that are sown too deep will not germinate.
3.5 Sowing Depth
Some seeds should not be sowed too deep, for 2 main reasons. Some seeds require light to germinate. Other seeds that are sowed too deep are not able to penetrate the surface and tend to die before they can emerge through the surface. The latter, will also be related to the soil media. Coco fiber for example is looser and lighter than sand, and thus is easier for seeds to emerge from the media.
Quick Guide to Germinating Different Seeds
Click on the species name to go to our product page for that plant.