Floating seed weed

How To Test The Quality Of Cannabis Seeds

Sowing dud cannabis seeds can prove to be a waste of time and effort. But how can you tell the healthy ones apart? Take a look at these tips for some guidance.

A lot of preparation is required before embarking on the quest of growing cannabis. Growers must ensure they have a good lighting setup to provide their plants with energy. They also need a designated area, indoors or outdoors, in which to cultivate their crop. Furthermore, growers will need a water source, an array of macro and micronutrients, and a good-quality soil if choosing this growing medium.

There’s another box that needs to be ticked off the list before growing as well, one that is often overlooked. Checking the quality of your cannabis seeds before placing them in the soil is a simple process, and one that can save a lot of time and energy in the long-run.

The most reliable way to check if your seeds are viable is to simply place them in the soil and allow them to germinate. Although this method is easy, waiting for them to pierce through the top layer of soil can take some time. This can be especially time consuming when growing on a large or commercial scale, or when simply wanting to get a grow started as quickly as possible.

Below are a few simple and easy methods you can use to assess the quality of your cannabis seeds.


Before we even get around to testing the quality of our seeds, it’s important to discuss where to source them. By purchasing seeds from reputable dispensaries, seedshops, and headshops, you greatly enhance the chances of your cannabis seeds being of good quality. Additionally, you will have the knowledge of exactly what the strain is, its characteristics, flowering time, and so on.

Some cannabis users might be thrilled to see a few cannabis seeds laying at the bottom of the bag of weed they just purchased. But this isn’t necessarily a good thing. As well as adding weight to the bag, there’s less of a chance that these seeds will be viable, and they are more than likely not feminized. Plus, there’s no telling exactly what strain they are and if their genetics are of any value. If you’re determined, there’s nothing wrong with attempting to cultivate these seeds; it could prove to be a fun side project. Just refrain from being overly optimistic from the get-go.


So, you’ve obtained some seeds and plan on germinating them soon, but you’re a tad unsure about their quality. Well, the first port of call is to take a closer look at them. This can be done with the naked eye, but using a magnifying device makes things a lot easier.

Healthy seeds usually feature a “tiger print” pattern upon the shell with intertwined colours of brown, grey, and sometimes black. Healthy seeds also often display spots on their shells and appear to have a waxy coating. Sometimes, however, seeds will appear green, white, or pale, which signifies a low chance of germination.

Healthy seeds are mostly hard to the touch and should be able to resist external pressure when placed between the index finger and thumb and given a squeeze. If your seed cracks under this pressure, then it’s a sign of a weak and unhealthy one.


If you’re buying from a dispensary or headshop, you might be able to inquire about the age of the seeds you’re interested in and get an honest answer. You’re far less likely to find out the age of seeds found in bags or acquired from other sources. Knowing the age of a seed before attempting to cultivate is beneficial, as seeds that are too old won’t end up sprouting, or will take a lot longer if they do.

Seeds are a life form in themselves, and are subject to ageing and deterioration. Although passing the point of being viable might take years, it’s still something worth considering before growing.


One cost-effective and simple trick to determine if your seeds are worth the time is to see if they float in water. Fill up a glass or jug with water and place your seeds on the surface. Leave your seeds in the water for a few hours and return to check on them later. Seeds that have sunk to the bottom of the water are healthy and should be germinated now that they have been soaked. Any seeds that remain floating on the surface are likely of bad quality and shouldn’t be used if you don’t want to risk wasting time.


If you have time to spare and are growing cannabis purely out of recreational joy, then you can simply go ahead and germinate the seeds. This is a 100% accurate way to determine whether a seed is viable or not.

Planting a seed into soil and waiting for it to sprout is one way to see if the specimen is healthy. However, a slightly faster way is to watch it germinate in real time. Place seeds between two pieces of paper towel and place them on a plate. Mist the towel with water until damp and store the plate in a dark spot. Check once a day and look out for any signs of a white tail emerging; this structure is called a radicle, which eventually becomes the primary root. Any germinated seeds can then be placed into the soil to sprout and become seedlings.

Floating Seeds in Water – Is This a Good Seed Viability Test?

How do you know if your seeds are still viable? Simple, do a seed germination test. Place the seeds in some water. The ones that sink are still viable – the ones that float are dead.

This advice is all over the internet so it must work? But how reliable is it?

Floating Seeds in Water – Is this a Good Seed Viability Test?; source: Pens & Pencils

Do the Floating Seed Test Properly

If you check out a number of sites that describe this test you soon realize that there are several different ways to do it. Some people add soap to the water to reduce it’s surface tension. Others put the seed in a jar and give it a good shake or they might soak the seed for 24 hours before doing the test.

There is no agreement on how to do the test properly. That means the test results reported on social media are not very reliable since they rarely include the details of the method used.

There are also silly claims like “this method is not 100% accurate and it only works with freshly harvested seeds of certain fruits such as melon, watermelon, cucumber, squash, peppers and tomatoes”. There are thousands of different types of seeds. Why would it only work on some vegetables and what does “not 100% reliable” mean? Maybe it only works 10% of the time?

Another site says, “the test only works for melons or cucumbers if the seeds are fresh and have not dried out.” So it doesn’t work on purchased seed. This same site went on to state that you need to ferment tomato seeds to get them to germinate, and I have already shown that this is a myth.

This gardening technique is so poorly defined that it is not possible to know how to do it correctly.

Citizen Scientists – Floating Seed Test for Viability

A number of gardeners have done tests to see how well the floating seed test works.

Pulsatilla albana ssp. armena – the Pulsatilla ‘seeds’ are actually fruits – achenes with “fluffy tails”, source: BotanyCA

I had some red pepper seeds from a store bought fruit and tried floating the seeds without drying them. Half floated and half sank. I removed the floaters and used them to try the test again. Half floated and half sank. I then tested this last group of seeds for germination. The ones that floated and then sank had 8/10 germinate, and the ones that floated twice had 3/10 germinate. So it is possible that floaters have a lower germination rate, but the floaters in this test were certainly not all dead.

I tested some Camassia seeds; 38 of 48 (79%) sinkers germinated and 12 of 16 (75%) floaters germinated, after a month in the fridge using the baggy method.

Someone from our Garden Fundamental Facebook Group tested Briza maxima (quaking grass) and found better germination with floaters.

Marijuana seed that floats will germinate on top of the water in 24 hours.

Twelve different kinds of pepper seeds were tested in this video and both floaters and sinkers had good germination.

I’ve germinated quite a few clematis seeds and most of them have fussy tails. They all float. Many seeds have this characteristic including some grasses and pulsatilla.

Both floating and sinking peppers seeds germinate, source: Daisy Dawes

The top picture in this post shows two jars. The one on the left contains black pepper seeds – they sink. You can distinguish them from papaya seeds that float, and are frequently added to spices since they look like black pepper but are much cheaper.

Science on Seed Viability Using the Water Float Test

Acorns have very low germination because many seeds don’t develop completely inside the nut and because various pests lay their egg in viable seeds which are subsequently eaten by the larvae. Floating them is a common way to eliminate many of the non-viable seeds. Even with this test, too much agitation of the water will cause viable seed to float.

Juniperus polycarpos, the Persian juniper, also produces a low number of viable seeds. Floating in water is not a reliable means of separating the good from the bad, but floating in a sugar solution does work. Sugar water has a higher density than water and this difference can be used separate seeds of various densities. The heavier viable seed sinks.

The float test “works well with hard-seeded peas in the family Fabaceae (e.g. Daviesia, Chorizema, Gastrolobium and Gompholobium) and Mimosaceae (e.g. Acacia), and has also been used on species in Hemigenia with good success. Do not attempt this test on seed of Allocasuarina. Allocasuarina seed is mucilaginous. This means it has a mucous membrane around the seed that gets very sticky on wetting.”

Arabidopsis seed forms a sticky mucilage on the outside of the seed as it absorbs water. Mutations of arabidopsis have been found that don’t produce this coating, allowing them to be separated from normal types with a float test. This is an example where within a single species, some seed floats and some does not, depending on genetics that has nothing to do with seed viability.

Arabidopsis wild seed (WT) sinks while a mutation (mum) floats. The floaters germinate in 24 hours siting on the water, source Helen M North

“Wheat was used in one set of experiments, and the average of all tests showed a germination of 68.3 per cent for the sunken seeds and 72 per cent for those that floated. In another set of experiments lentil was used, and it was found that 75.4 per cent of the sunken seeds and 86.7 per cent of those that floated germinated.”

The floating characteristic of seeds depends very much on their weight, surface coating, shape and specific gravity. Some seeds do develop a large seed coat which can be empty and these likely float. The specific gravity of a seed is controlled by the environment (moisture) and internal enzymes and hormones. Some dead seeds sink, while some spongy seeds like spinach float even if viable.

Does The Seed Float Test Work for Testing Viability?

There are cases where a float test can be used to identify viable seed, but when science reports on these they are quite specific about the type of seed and the method used.

On the other hand gardeners tend to simply lump all seeds into one category and say they all work, without specifying the method that works.

As a general rule, gardeners should assume that the float test does NOT work for testing seed viability, unless there is evidence it works in a specific case.

A Better Way to Test Seed Viability

Use my baggy method if you want to test seed germination. You will actually see the root come out of the seed and know for certain that the seed is viable.