You 'can' disassemble the planting and add perlite if so inclined, but it's unlikely you'll be pleased with the results. Here's why:

When you start with a medium comprised of a very large fraction of fine particles and try to amend it by adding perlite, the o/a % of aeration goes down, not up, and it makes very little difference in drainage. Those who think they are doing something beneficial by mixing equal volumes of a poor potting medium and perlite are actually shooting themselves in the foot.

Imagine you have a jar half full of peat and a jar full of marbles. Start adding marbles to the peat. Soon, you have a full jar of the peat/marbles mix, but you have exactly the same amount of aeration you had in the the half jar of peat, so the o/a % of aeration has decreased by 50%. Adding perlite is little different than adding marbles. Perlite has no internal porosity, which means each perlite particle decreases aeration by something slightly less than the volume of peat the perlite displaces.

So, when you start adding coarse material to a large fraction (in some cases 100%) of fine material, aeration becomes steadily worse until something called the 'threshold proportion' is reached. The 'threshold proportion' describes a medium that has exactly enough and no more fine particles required to fill all the spaces between the coarse material in the medium. This is the most difficult soil to grow in. In fact, a grower is better served, but that is not to say 'well' served, to use only the fine material than to ad coarse to fine and not go beyond the threshold proportion. Typically, if a grower wants to enjoy the considerable advantages offered by media made of large fractions of coarse material, the coarse material (1/10 - 3/8") should be >80% of the mix. So unless you're ok with the idea you're having coffee with your cream when only using a tablespoon of cream in a cup of coffee, you can't amend a soil that's too water-retentive by adding coarse material; this, because by the time you arrive at the threshold proportion, the overwhelming % of the medium will be coarse material.

There are some things you can do to limit the amount of water a planting can hold, but when you're measuring watering intervals in months, the probability there will be serious loss of potential or even loss of the plants' viability is very high. Oxygen is as essential as water to the root system. A dearth of oxygen means poor root function or health, both of which take hope of having a healthy plant out of reach. A healthy root system is a prerequisite to a healthy plant.

These 'containers' are full of grow medium. The shaded area is perched water, something the soil you're using has much of. Note how tipping the pot (compare B to A) reduces the amount of perched water a planting can hold. D shows how adding an over-turned pot significantly reduces the excess water. E shows use of a wick, but it's doubtful that, even if employing more than one of these work-arounds, it will be sufficient as a remedy for what you're dealing with.

Al

Hi Al

Thank you for your thoughtful comments and explanation.

If I read your message correctly, it seems to me that I need to start from scratch and plant them in a better draining soil mix.

I also read many many messages on your 5:1:1 mix. I am trying to figure out how to source all the material in Austin, Tx. Hopefully this will help revive the plants :-).