Try to remove as much soil as you can and don't forget that coco is hydro so drop your ph to 5.6 - 6.0 and if your water is low ppm or ro then get some calmag too.
people keep mentioning calmag for RO water. i am not convinced because i have been using RO water now for 2 grows and i never use it, yet no symptoms of deficiency at all. i should research that more.
anyway, i had this problem and indeed i felt the need to get rid of all the soil before placing in coco. i would suggest one of two methods depending on how big your plant is.
if your plant is young/small and doesn't have a huge rootball, try and rinse the soil off the roots using PHed room temp water with no nutes. don't run it under the tap, the high PH, possible extreme temperature and force of running water could shock your plant all to hell. you could try setting it in a bucket with the water and an air stone and gently massage the roots every 5 minutes to remove the soil, leaving it to soak the rest of the time. make sure you use an air stone though, treat it like DWC, you dont want to stress your plants by drowning them. change the water out when it gets really mucky and continue until your roots are clear of medium. repot in coco burying the stem about an inch or sodeeper than it was before (you may need to lollypop it a bit depending on how much stem you have to the first node) so it is stable. gently compact the coco in 1-2 inch layers as you go, nothing harsh, just so the coco is not fluffy. build up keeping your plant centered and straight as you go, and then you are done. give it a good healthy watering with about 3/4 strength of the solution the plant had before (you cannot overwater now you are in coco) until you see as much water coming out the bottom of the pot as you are putting in. you can switch back to full strength in a couple of days.
now if you have a bigger plant that has a tight root system, you are going to have to do your best to loose out the soil from around the root ball. do NOT use water for this one, it just makes everything more difficult. wait until the plant is in need of a feed. don't dry the poor thing out completely, but you want the soil barely moist. take the rootball, gently work the outer roots free while the soil drops away. be careful not to rip any roots from within the main ball and keep the ball supported. that soil is heavy and roots are not known for their tensile strength. work away the soil bit by bit until you get to the point where you cannot physically get any more soil out without ripping or cutting roots apart. you will end up with a ball of soil in the middle, and the rest will be replace with coco. this is the best you can do. repot in layers like the method above, and you are sorted.
this second method is what i had. and i tried to do it like the first method. HUGE mistake. it made a right mess and the soil didn't want to leave the roots at all! i just ended up nearly drowning the poor thing. this plant ended up being about 3 inches shorter than all the rest by the time i harvested. maybe coincidence, maybe i shocked the poor thing and it took longer to recover.
now pay attention if you are using hydro watering systems on timers etc. now what i made sure after the rootball was now half and half, is i only watered around the edge of the pot, not directly over the area with soil. take note i use a wilma dripper system and i use a dripping tube that forms a ring. this waters my plants for a solid 15 minutes each day on a timer. not the sort of situation you want with soil. so when the plants got watered, the water was running through the coco on the outside, and naturally retaining just enough moisture as coco does (great stuff, it is). the soil ball on the inside doesnt get watered directly at all, instead it draws its moisture from the coco via capillary action. this ensures the soil doesn't get over watered as it cannot handle hydroponic style flooding.
so say your pot is a 12" pot, so your radius is 6" and you managed to free up 3" of roots and replaced that with coco. you now have 3 inches from the edge of the pot to the edge where coco meets soil. you want to water in the middle of this 3" band of coco, so 1.5" from the edge of your pot. i use about 2 feet of air hose with little notches cut out along 1 foot of it, with a knot tied that end, and i form a loose ring around the pot wherever i want. when the water goes through, it acts like a ring dripper, but a flexible one. plus it is a lot cheaper than buying the drippers ready made and a lot easier to clean them too.
sounds like a lot of work but it isn't when you get into it, and you will not regret swapping to coco. just remember though, coco is a hydroponic, sterile medium. you need to adjust your nutes to suit, maybe change your nutes all together if they are designed for soil, and water a bit more frequently. good luck with the transplant and let us know how you get on.
happy growing
