I've never seen any proof offered to support that, I top all of my plants be the photos or autos, I can't make the argument that topping a plant reduces growth to any material extent based on plant biology.
My first five or so grows were autos and I've done a few photo grows since then. The reason I switched is because autos grow on their own schedule and, in my experience, they just get too big for my 2' x 4' x 8' tent.
Can you get a bad crop from an autoflower? Of course and you can get bad results from a photoperiod plant. I've only been growing 3 ½ years but experience has been that if you give cannabis a lot of light, keep temp and RH in range (VPD), prune it as little as possible, and give it as few nutrients as it needs, you will have a bountiful crop. Autos or photos makes zero difference.
Two Gelato autos in the tent. Mary is hiding on the left side while Jeff is the huge SOB on the right. Two lights in the tent, a 330 light at the top and a 125 watt Vipar XS 1500 for the front row.
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This is a topped and LST'd photo. Really nice to work with and easy to harvest.
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A great example of "begging the question" because your assumption is that yield will be lower. Again, show me the data. I always top and LST my plants because they're valid techniques to maximize yield.
Topping a plant removes the apical stem so growth hormones flow to the nodes below where you topped. That makes it easy to have an even canopy and because the canopy will be more even on a topped plant, the "PPFD map" is more even and, overall, the plant gets more light. Given that light is the only way that plants make food (nutrients are
not food) a canopy that is more even will, all other factors being equal, produce a higher yield than a plant that is not topped.
You're going to run into a height issue. I would recommend that you top and LST your plants and given them as much light as they can handle. In addition to high light levels allowing the plant to produce the most glucose, plants that receive a lot of light will tend to be shorter and more compact, with a larger number of small leaves. In contrast, plants that don't get much light will stretch toward the light source and will tend to have fewer, larger leaves and few branches. That results in a tall, skinny plant with few bud sites.
In the case of a 4' tent, you have very limited head room so topping+LST+lotsa light are the way to go.
I really like AC Infinity products. I've got six pieces of AC Infinity equipment in my 2' x 4' tent and have a used three or four models of their controllers. I've used Pulse, Inkbird, and AC Infinity devices and AC Infinity is, by far, the best.
With their lights, you'll want to use high hang height because at lower hang heights, it's hard to get an even light cast. Money spent on a lux meter is money well spent
if you want to maximize yield. A lot of growers just want to "grow some weed" and cannabis will do just fine by them. We know that crop yield increase in an almost linear manner as light levels increase so, if you do put the time into getting "lotsa light" on your plants, you may well end up with shit ton of weed because cannabis
is a light whore loves light.
My experience is that when cannabis is given a lot of light, in good temp and RH ranges, and well maintained (top, LST, and resist the urge to remove leaves), a cannabis crop will easily meet the yield estimates that seed sellers provide.
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Which light meter? I've used and tested the Uni-T light meter (I use an Apogee PAR meter). It's only $24 on Amazon and gets the job done. The BTMETER BT-881D is more expensive but it has a record feature so you can sample multiple points across you canopy. With a 2' tent, the Uni-T will do fine but if you're thinking of going to a larger tent and want to maximize the amount of light your plants are getting, the extra $4 for the BT-88 might be a better purchase.
I've attached a document I wrote about converting lux to µmol. Based on the spectrum of your light, a factor of 0.0145 or 0.015 will give you a pretty good number.
It will keep your plants short and bushy. Just need some wire to die down the plant
