CactiJim wrote: ↑Tue Aug 25, 2020 9:58 pm
What an amazing post; so much beneficial information.
Quick question: do you guys think spraying neem oil on the soil mixture before sowing seeds would have a negative impact on the seedlings, or would it just help prevent fungus/mold?
Late reply here but neem oil is generally more effective when used, repeatedly, on pests like thrips, mealybugs, scale, etc. I don't actually know about the effectiveness of azadirachtin (the active ingredient) as an antifungal, much less as a preventative antifungal. I can say that neem oil does not have a very long shelf life so it's usually better to buy the cold-pressed concentrate, mix what you need for application, apply as a topical spray and/or soil drench, and discard the rest. It works more effectively over time as a growth hormone disruptor and anti-feedant vs. an immediate contact kill product although it can effectively suffocate some soft-bodied pests by virtue of it being an oil. Multiple applications over a six-week period generally works best to control most pests and the frequency of applications can vary depending on the life-cycle of the pest you're targeting to ensure you're also getting the new generations as they're born. It's always important to remember that neem oil is generally not phytoxic but the oil residue will increase the photosensitivity of the plant and thus should be washed off with plain water before exposing the plant to intense light again.
I actually came here to share some basic seed cleaning/preparation practices that I feel many here may benefit from if they, like me, lack formal education and training in horticulture. A free manual from the US Fish and Wildlife Service (link here to the PDF:
https://www.fs.usda.gov/rm/pubs_series/ ... gtr274.pdf) about growing native plants has some great 101-level information.
Of particular interest to me was the section discussing a running water rinse for seeds prior to stratification or scarification. According to the manual this helps threefold:
- ensures seeds are well hydrated. This is often a prerequisite for any stratification attempts to be effective
- effectively removes or dilutes naturally occurring chemicals on or within the seeds that prevent germination
- effectively removes bacteria and fungi from seed coats
Edit: adding screenshots so you don't habe to hunt for the info I'm talking about
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In my opinion, all of those are valuable services but the last one is particularly interesting because the seed coat is often the vector of fungal and bacterial infections that people seem to struggle with even after the've gone through the hassle of sterilizing their soil, equipment, pots, workbench, etc. I know some people have used bleach or peroxide to attempt to sterilize the seed coats but, to me, that is riskier than just running water.
I realize that cacti seem rather different from most native plants that are popular across the US, particularly the Midwest/East where I'm from. But, as we've all learned thanks to the vigorous discussions around fertilizers and nutrition here, cacti are oftentimes *more* similar to the common roadside weed than not and the same basic horticultural practices one would use in say, turfgrass management, can even be applied with success to growing cacti. On that note, I think there is a lot of potential to approaching seed-growing some of the more "difficult" species through the lens of stratification.
Last year I received seeds of Mammillaria herrerae from a member here and struggled to germinate them. Through 3 cycles of being kept moist and warm in an incubator for 2 weeks and then allowed to dry out before rewetting and trying again, I had 0 germination. For context, I'd planted 15 other species and while germination was poor on some, there *was* germination in every other pot but not the M. herrerae. Until, that is, I put the pot outside in frustration and left it alone under some window screen but otherwise exposed to the elements. After an unusual spring drought and heat wave rolled through my area, the rain returned and immediately following the initial 2 day downpour I had 7 or 8 M. herrerae germinate.
Since then, I've often wondered about what exactly it was that caused the M. herrerae to sprout. Were they simply dehydrated and they needed the deluge of rain to kick them in gear? Did the rain aid in washing off some sort of naturally occurring chemical on the seed coat that was preventing germination? Was the hot/dry spring a necessary trigger for the seeds, simply a form of stratification that is the inverse of the cold/moist stratification needed by many Midwestern native wildflowers? Do the seeds of M. herrerae have double dormancy mechanism similar to that of trilliums; do they need some sort of combination of a period of moist/warm conditions followed by moist/cold conditions, followed again by moist/warm conditions before they will germinate in high numbers? What if one of the moist/warm periods a plant like yew or trillium requires should actually be *dry*/warm for M. herrerae? Given their native environment, I would not be hard-pressed to believe that Mammillaria herrerae and other cryptic mammillarias may have dormancy mechanisms that function to suppress germination during the most extreme times of the year which are generally hot/dry. An examination of climate data may reveal cyclic patterns that are longer than a year which could make a case for a double-dormancy mechanism or something similar.
Regardless, I think a starting point with a lot of potential for hobbyists and members here would be to experiment with a running-water rinse as a general best practice and to consider the possibility of some hard to sprout seeds having internal dormancy mechanisms that could benefit from some type of stratification. I plan to experiment more but I'd love to know if anyone else has thought about this or tried some form of stratification with success (or failure).