A female cannabis plant sprayed with silver grows male flowers, and her pollen carries only X chromosomes. Seeds made with that pollen grow into female plants. This part explains how to choose the two plants, collect and store the pollen, pollinate without seeding your whole room, and harvest and store the seed.
The sprayed female is called the donor. She is not safe to consume, so you destroy her after she has given her pollen. The female you pollinate is the seed mother, and she is never sprayed. Part 1 covers safety, the biology, how to mix silver thiosulfate and the spray schedule.
This is Part 2. Part 1: Making Feminized Seeds: The Silver Thiosulfate and Colloidal Silver Methods, Step by Step
7. Choosing the donor and the seed mother
7.1 What to select for
The donor’s pollen goes into every seed, so choose her carefully. The topic on phenotype hunting explains how to find such a plant in a pack of seeds. Look for:
- vigour and good structure;
- resin and the terpene (aroma) profile you want;
- disease resistance;
- finishing time;
- stable flowering over more than one run.
For the seed mother, look for:
- space for the calyces, the small pods around each flower that swell as the seed grows;
- branches you can reach with a brush;
- vigour late in flowering;
- a line that adds something the donor lacks, if you want a cross rather than a self.
If the donor and seed mother are the same plant or clones of it, the seed is an S1: a plant pollinated with her own pollen, which breeders call a selfed line. If they are two different plants, the result is a feminized cross. Keep a clone of each parent until a germination test shows the seed is good. If the seed fails, you can then repeat the cross with the same plants.
Translator’s note: If you buy clones from another farm, you can bring in pests or hop latent viroid, or end up with a variety that is not what the label says. Before you use a bought clone as a donor or seed mother, keep it apart from your other plants and check it carefully. Then flower it once and confirm it is the variety you were promised.
7.2 Never reverse a plant that has shown intersex flowers
This rule is a convention among breeders, not a measured result, but almost every breeder follows it. Some plants grow stray pollen sacs on their own, for example when light leaks into the dark period or the room gets too hot. Breeders treat that unstable sex expression as inherited. If you reverse such a plant, every seed carries the same weakness.
You want stamens to appear only after the silver spray. If any appeared earlier, the plant is ruled out.
Flower the donor once without any treatment first. Until you have flowered a plant, you do not know whether her sex expression is stable.
Translator’s note: In the Thai hot season, many plants go through heat stress. That makes the untreated test run more useful. A plant that stays fully female through a hot run is a stronger donor candidate. Record the room’s highest temperature during that run, so you know what the plant was tested against.
What to do: keep a short record for each donor candidate. Note how many runs she has flowered, the highest temperatures, and whether any pollen sacs appeared.
8. Controlled pollination
Cannabis pollen is extremely fine, and the smallest air current can carry it. It stays alive long enough to seed every flowering plant in a room. Each step below is designed to keep the pollen only where you put it.
8.1 Isolating the donor and collecting pollen
Move the donor into a separate space with its own exhaust before the first spray. When the anthers split open, put paper or clean glass under the flowers and let the pollen drop. You can also tap the branches gently over the paper.
Collect over several days, because the anthers open in batches rather than all at once. Turn off all fans while you work and wear a mask. Sieve out plant debris, because it holds moisture and moisture kills stored pollen.
8.2 Drying and storing pollen
The best evidence comes from a 2020 study in the journal Plants. The researchers developed a germination test and a storage method for cannabis pollen. For practical home storage, see also storing seeds and pollen.
| Practice | What the 2020 study found |
|---|---|
| Mixing with baked whole-wheat flour, 1 part pollen to 10 parts flour | Essential. The flour carries the pollen and absorbs moisture. |
| Drying under vacuum at 5 kilopascals (about one-twentieth of normal air pressure) for 40 minutes | Best method tested. Weaker vacuums of 15 and 25 kilopascals gave worse results. |
| Storage at 4 °C (fridge temperature) | Even the best sample germinated at only about 22% after 21 days. |
| Liquid nitrogen after drying | Storage for 24 hours and for 4 months gave almost the same results. |
Fresh pollen germinated at about 33–50%, depending on how far into flowering it was collected. The researchers also tried protective chemicals used for freezing cells: dimethyl sulfoxide and glycerol at 10–60%. Both killed the pollen completely.
The study tested only 4 °C and liquid nitrogen. It gives no figure for a household freezer at −20 °C. Breeders do use household freezers, with flour and a moisture-absorbing sachet, and they report pollen lasting for months. Pollen that had not been dried died completely in liquid nitrogen, because wet pollen does not survive freezing.
So use fresh pollen within the same week if you can. If you take pollen out of cold storage, let the sealed container warm to room temperature before you open it. Otherwise water condenses on the cold pollen.
Translator’s note: During the Thai rainy season, the air is often above 80% humidity, and dry pollen picks up that moisture quickly. Collect and sieve pollen in an air-conditioned room or next to a running dehumidifier, and seal it quickly. Most home growers do not own a vacuum pump. The flour-and-silica-gel method breeders report is the realistic home option, but no study has given a figure for it. A power cut that thaws the freezer causes the same problem as opening it cold. Split pollen into small sealed portions, each with its own desiccant. Then one thaw or one opening only affects one portion.
8.3 Brushing, bagging and labelling
- Choose branches about 14 to 21 days into the seed mother’s flowering. At that point the pistils (the white hairs that catch pollen) are white and receptive, and the calyces have not started to swell.
- Move the seed mother out of the main room into a separate space with the exhaust and fans off. Dab pollen onto the pistils with a fine brush that carries only a little pollen. A brush with too much pollen releases it into the air.
- Bag the branch in a paper bag tied at the stem for about 24 hours. Paper breathes. Plastic traps moisture and can rot the flower.
- Remove the bag and mist the branch lightly with plain water, which kills stray pollen outside the bagged area. Tag the branch with the names of both parents and the date.
Afterwards, wipe surfaces with a damp cloth instead of sweeping them dry, because dry sweeping puts pollen back into the air. Change your clothes and wash your hands before you go into the flowering room. Assume that every flowering female in that air without a bag has been pollinated.
What to do: before you open the pollen jar, prepare paper bags, string, tags and a spray bottle of plain water.
9. From pollination to ripe seed
| Time after pollination | What happens |
|---|---|
| 24–48 hours | Fertilisation. The pistils darken and shrivel, which is the first sign it worked. The calyces swell within two weeks. |
| Weeks 3–6 | The seeds form. They start soft and pale, then harden and darken. The seed mother often finishes flowering in this period. |
| Weeks 6–8 | Most varieties reach full maturity. Some calyces split open and show the seed. |
The window most often reported is six to eight weeks. Fast varieties take closer to five to six weeks. Long-flowering narrow-leaf varieties can take up to ten. These figures come from breeding guides, not controlled trials, so use them for planning only. Decide when seeds are ready by how they look.
| Ripe seed | Immature seed |
|---|---|
| Brown or grey, often with tiger stripes | Pale green or cream |
| Hard, does not give when pressed | Soft |
| Glossy, with a visible ridge | Matte |
| Loose inside a calyx that is splitting | Still held tightly |
Remove the seeds by hand instead of threshing, which means beating or rubbing the flowers to knock seeds out. Throw away seeds that are pale, soft or flat.
Air-dry the seeds at room temperature for one to two weeks before sealing anything. Sealing seed before it is fully dry is the most common way home-made seed is lost. Then store the seed in an airtight container with a silica gel sachet, somewhere cool, dark and at a steady temperature. Label it with both parents, the pollination date, the harvest date and the generation. A month later, test a small sample to see how many germinate.
Translator’s note: In the Thai rainy season, room air can be so humid that seeds do not dry properly. Dry them in an air-conditioned room or next to a dehumidifier. Check that they are hard and dry before you seal them. Without the germination test a month later, you only find out the seed was bad at sowing time, after the parent clones may already be gone.
10. Limits of feminized seed
10.1 No males, and a shrinking genetic base
A feminized batch contains no males, by design. That leaves no pollen donors for the next generation unless you reverse another female. Many breeding methods need real males. These include backcrossing (crossing offspring back to a parent), developing a stable line, and testing one father against several mothers. So you cannot keep breeding a collection the usual way if every seed in it is feminized.
There is a slower cost as well. Feminized lines are usually built from a few proven mothers that are often related. Repeated feminized work therefore tends to shrink the line’s genetic base, meaning the range of genetic variety in it.
Traits nobody selected for can quietly disappear because nobody tested for them. Examples are root vigour, climate tolerance and resistance to a disease that was absent at the time. This matters most where conditions differ from the indoor rooms in colder northern countries where most commercial lines were developed. That includes Thailand and the rest of the region, home to Southeast Asian landrace cannabis.
What to do: for any line you want to keep developing, also keep regular seed or male plants. Regular seed produces both males and females. Use feminized seed for producing crops, not as the only copy of your genetics.
10.2 Hidden recessive traits in S1 seed
An S1 is close to a plant pollinating herself. That brings together recessive genes, which only show when both copies are present. Crossing with an unrelated plant would keep those genes paired with normal copies and hidden.
In the grow room, this shows up as inbreeding depression: weaker growth, smaller plants and lower yield. Hidden recessive traits also appear, such as albino or patchy-coloured seedlings, poor germination and weak roots. The plants are also less uniform than growers expect, even when all the seed comes from one mother. Any hidden tendency toward intersex flowers also becomes visible.
That does not make S1 seed bad. An S1 keeps something close to a plant you like and shows what she was hiding. It does not improve the line. To improve a line, you need more parents, not fewer.
What to do: record every attempt, including:
- variety;
- silver form and strength;
- spray dates;
- days to the first male structures and to pollen;
- how the pollen was stored;
- pollination and harvest dates;
- germination rate.
11. The Thai legal side
Translator’s note: Cannabis flower is a controlled herb in Thailand. This is set by the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568. The notification was issued under the Thai Traditional Medicine Protection Act B.E. 2542 and has been in force since 26 June 2025. Flower may be sold only with a PT 33 (ภ.ท.33) prescription, which covers at most 30 days. Advertising flower and selling it online are prohibited.
Translator’s note: The Ministerial Regulation on Controlled Herbs (No. 2) B.E. 2569, in force since 30 April 2026, made the licence criteria for cannabis flower stricter. Under Section 78 of the 1999 Act, selling or processing a controlled herb without a licence carries up to 1 year in prison, a fine of up to 20,000 baht, or both. All flower from a breeding project falls under these rules, seeded or not. The sprayed donor is waste and never a product.
Translator’s note: For what is currently legal for seeds, see buying cannabis seeds in Thailand in 2026. Read the original legal texts before you act or post an offer.
Share your results
If you have reversed a plant, post your numbers below this topic. Give the variety, the method (silver thiosulfate or colloidal silver), the strength, the days from the first spray to open anthers, and your germination rate. The dose that works differs between varieties. Data from members on locally adapted Southeast Asian varieties is therefore worth more than any single published protocol. Failures count too: tell us the age of your solution and the strength you used.
References (Part 2)
- Gaudet D, Yadav NS, Sorokin A, Bilichak A, Kovalchuk I (2020). Development and optimization of a germination assay and long-term storage for Cannabis sativa pollen. Plants 9(5): 665. https://doi.org/10.3390/plants9050665
- The spray studies and protocols behind Sections 1–6 are listed at the end of Part 1.
This article is part of the Asiannabis Community educational series on cannabis genetics and breeding. It is for education within jurisdictions where growing cannabis is legally permitted.