How to grow cacti from seed
The purpose of using the baggie method to raise cacti from seed is to maintain humidity during germination and ensure sufficient water is available to seedlings during early stages and to prevent pests and diseases affecting young plants.
It can be somewhat labour intensive to begin but is a method that is basically set and forget.
This method serves to replicate “nurse plants” as found in nature. Nurse plants are established plants which provide protection for seedlings whilst they establish. The main points of protection are increased levels of shade and also an increase in moisture which is vital for young seedlings.
The baggie method takes advantage of the ability of young cacti to not only survive but thrive in conditions which are constantly humid and have high levels of moisture.
Certainly not conditions you could subject older cacti to.
Cacti seedlings not only survive but actually do exceptionally well for up to one full year. Possibly even longer but generally a full seasonal cycle is sufficient time to have good sized seedlings.
The baggies method is particularly useful for the slow growers like Aztekium, Blossfeldia and Strombocactus just to name a few.
So How Do We Do It ?
Cacti seeds will germinate in basically any moisture containing substrate from a paper towel to garden soil.
There are countless options for what substrate mix to use and many growers will have their tried and true substrate which they swear by.
Substrate does not need to be overly complex but there are some points to consider, especially if you are intending on leaving seedlings in the bag for a full seasonal cycle.
From experience, I recommend the mix you choose allows for good airflow around the roots to prevent damping off and seedlings rotting. To achieve this the mix should be high in inorganic materials.
A simple but effective recipe is as follows:
• 1 part potting soil (sifted through a coarse sifter)
• 1 part coconut coir (fine grade)
• 0.5 part coarse river sand
• 1 part fine perlite
• 2 parts fine gravel/stones (any non reactive gravel)
Examples of suitable gravel - scoria, pumice, quartz, bluestone chips,
Sizing should be 1mm-7mm.
Rinsing gravel will assist in removing the fines which can clog up a substrate mix.
Close up look at our seed raising mix
Conditions within the baggie will be warm and high in moisture which is a prime environment for bacteria and other nasties. Treatment of the substrate is necessary to eliminate these or they will take over the pot and seedlings.
• Mix the substrate well and put in a metal oven dish with enough water so it is thoroughly soaked. A small puddle or two are acceptable but the mix should not be under water.
• Cover the dish with foil and bake at 200c for 30 minutes. Mix thoroughly and then re-cover with foil and bake for another 30 minutes.
• If at the half way point the mix is too dry, add a little water.
• If the mix is too wet then remove foil for the last 15 minutes of baking.
• DO NOT add water after baking as this will introduce spores, bacteria, etc. Foil should remain on or be replaced after baking and tightly sealed.
Mix thoroughly post baking and cover with foil tightly whilst it cools.
Allow soil to cool for 1 hour (this is usually enough time)
Note — From personal experience, I don’t recommend using the microwave for substrate treatment. The microwave doesn’t hold the mix at the required temperature long enough to kill certain nasties which seem to survive short bursts of microwave treatment.
A delicious mud pie
Once cooled, your substrate is ready to use and we will now move onto the fun part.
Mix the substrate thoroughly before you tray up your pots.
Push the mix into pots as it will generally shrink a bit over time and leave a gap around the edge but isn’t a huge problem.
Rough up the substrate with a fork relative to the size seed you are planting. Plants like Astrophytum have large seeds and will drop into the pockets.
For very small seed use a light poking action with a fork to make sure the surface isn't super smooth from pushing the mix into the pots.
Once seeds have been sown on the substrate mix we will apply another preventative to ensure no nasties are being introduced by the seeds themselves.
This will be achieved with a spray of 3% hydrogen peroxide (generally available from supermarket personal care aisles in a brown bottle). Apply this treatment twice.
The first once the seeds are sown, and the second after a top dressing is applied.
The top dressing is the same gravel as used in the substrate mix.
To prepare the gravel, wash thoroughly in a 10% bleach solution.
Rinse it thoroughly and then bake in the oven until completely dry.
Top dressing should only LIGHTLY cover seeds.
Depending on seed size, a single grain depth may be all that's required.
For very fine seeds I recommend applying the top dressing PRIOR to planting the seeds. They will settle amongst the gravel and this prevents them from being planted too deeply. In this case, spray with peroxide after the top dressing is applied and then again after seeds have been sown. This assists in the seeds settling into the gravel pockets.
Ready, set.... sow!
Alrighty... !! The seeds have hit dirt and the top dressing has been applied. The treatments have all been applied and now we will pop them into the bags. So which bags do we use?
For the 63/68mm square pots, sandwich size zip lock bags will suit perfectly. For seedling punnets, (the ones used for veggie seedlings), the large sandwich size zip lock bags will work nicely.
My personal preference are the Hercules® brand bags which are available in most supermarkets. The zip locks are good quality and will actually last for the full seasonal cycle.
Keep the bags somewhere with heavy shade.
The goal is to provide soft conditions which will enable the seedlings to thrive. If they are in a full sun position, a double layer of 70% shade cloth works well. In a slightly shaded position just adjust the shade cloth accordingly.
Once the seedlings have reached a desired size or they look like they've had enough of being in the bag, a slow acclimatisation will be required. Open the corner of the bag just a little and then slowly increase the opening size over the span of a week to 10 days. Once the seal is fully open, leave the seedlings in the fully open bag for another day or two and then they can be removed.
It is best to plant the majority of cacti seeds during spring.
Use treated substrate mix within 48 hours to prevent the mix becoming re-infected with nasties
It is better to provide too much shade than not enough. Stretched seedlings are easier to fix than scorched ones.
Substrate mix should not be too wet or too dry. A little water pooling in the bottom of the bag is ok.
If nasties do pop up they will most likely occur within the first few weeks and can be treated with 3% peroxide.
This will not harm the seedlings
Seedlings should be checked weekly for the first few weeks. Once settled, monthly, or even quarterly checks will suffice
As you approach the 6 to 9 month mark, some seedlings may have had enough of being in the bag and start to rot. This is a sign they are ready to come out and need to be removed regardless of the season.
Slowly open the bag over a week to 10 days.
The principles of this method can also be applied
to “Take-away Tek”
Thank-you for reading and best of luck!
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