I don't think there's any real harm in packing them in tightly, but there are pros and cons. Pro: rooting plants in close proximity seem to root faster, start growing more quickly. In fact, I've got two or three "community" rooting pots - largish (8", 10") pots with soil in them that I can, on a whim, toss a cutting into when I don't feel like taking the time to give it its own pot. I find they root very fast this way, and I think it's also true when a lot of little rooting pots are crammed close together. I think some of it is that rooting plants are throwing off rooting hormones, maybe even rooting "vibes" that give others... well, let's call it inspiration! But it's probably more about the micro environment it creates. Sharing humidity, etc. But you do have to keep the air moving around them or it's easy to develop mold...

Cons: it's hard to examine them closely when they're crammed together. It's easy for buggers to slip in there and make themselves at home. It's a more desirable environment for fungus gnats. And when they do start to grow, they get entangled.

My rule (for the most part...) is it's ok to grow them this way as they are rooting. I make it a point to pull the whole tray off the shelf and do a thorough examination of every plant periodically to make sure there is nothing negative going on. And as soon as I see new growth on one, it gets pulled out and given some room to grow. (Not that ANYone at my house has much "room to grow" LOL!)

Anyway, they all look awesome. You're definitely doing something right!

Denise in Omaha

I suppose it's up to you, how much space you've got & how entangled one'll allow them to get. Also of course, how many one has right? ;>) Yours all look very happy.

Here's one corner of my kitchen, West window; the baskets are mostly Hoyas, sorry the shots are distant.

Then next to it, perpendicular to the West window w/ great afternoon light are more plants, Hoyas & top row are Sans.

It used to be packed tighter when I had more, but less so these days & after the Hurricane losses.

I've got still more Hoyas under those shelves on my kitchen table, but just a few,w/ some other plants too, like my basket of Hydro Sans. which a friend called AquaSans.

That's my adored varieg Macrophylla in the middle & my large leaf guys on the left, Clandestina & Polystachya.

I'll have this situation with I start moving them back in the Fall.

Ha - mine look just like that.

I wouldn't claim it's ideal, but neither would you, right? ;) Idyllic would be every leaf getting perfect exposure to outdoor sunlight, with heat and humidity so thick you could cut them with a knife, unpolluted rainwater and a smorgasbord of pungent mature organic fertilizer.

But they don't always experience idyllic life in the rainforest, either, so I think it's important to make a distinction between (a) environmental conditions that endanger plant health and (b) environmental conditions related to fast growth.

Air Flow:

I have zero problems with air flow. I do run a nearby ceiling fan constantly. I 100% agree with Denise that grouping them together creates extremely beneficial micro-environments of humidity. My closely spaced plants are much heartier to drought and other human-related indignities.

Light:

I try to keep plants of a similar size (height + leaf size) together. That way I don't have a big meredithii playing umbrella over a starter pubera. It can be more challenging to line up a row of mindorenses (mindorensis plural I just made up), rather than spacing them with small leaf varieties in between, but that's how I know they're all playing on the same field. But I think it's more important that they all have leaves reaching the top level, close to the lights.

Bugs:

The biggest challenge, as Denise points out, is that the closer the plants are together, the more bugs are obscured from your vision. I don't ever have a problem with fungus gnats because the plants dry out, but if you are prone to an occasional mealy or scale outbreak, you really have to be thorough and not-lazy during inspections. And it can be challenging getting pesticide coverage to the inner layers without taking the whole flat apart. That is why I am the BIGGEST FAN EVER of my latest switch to putting similar-textured-leaves together. Now I can check flats of finlaysonii more casually, but pay A LOT of attention to flats with delicate leaves like megalantha or soft leaves like diptera. The best thing, if your plants are closely spaced, is to have no pests, like Doug. Can't we all try and be more like Doug, guys? ;)

Tangles:

I don't actually have a lot of problems with tangles because new growth primarily occurs near the light source. So, they all lay their new vines neatly along the top of the flat (or out to the side), where I can deal with them once they are long enough to loop without putting new growth down.

I did have that problem with all the lacunosas turning into one giant knot, but that flat went ungroomed for years and a lot of it had to do with their internodes being so short, so their leaves linked together just like they were weaving a mat.