Looking back, I got SO much wrong in the early days when I first started experimenting with semi-hydro for my houseplants.
My two biggest stuff-ups were how I switched my plants from growing in potting mix to shift them to leca or pon, and also getting the water side of things really wrong (especially skipping flushing, rookie mistake).
There's a LOT of great advice out there for sure, much more these days compared to when I first started with semi-hydro.
But as I found out the hard way, a lot of that advice depends your plants being little angels, who behave perfectly, doing everything they're expected to. But the reality of semi-hydro can be VERY different.
Here are the many lessons I learned along my semi-hydro plant journey. I'm a big fan of preventation, but I've shared lots of problem-solving here also in case you're facing the same problems I did, as well as answers to common semi-hydro FAQ's, how to prep plants, how to decide whether to use leca or pon, what to expect after you switch, and so much more. Let's do this...
Lesson #1: You're growing in water (not leca or pon)
Imagine leca and pon more like scaffolding, there to support your plant's roots, rather than just another substrate like potting mix, fern fibre, bark etc.
Unlike most substrates, leca and pon by themselves provide pretty much ZERO nutrients. That's why fans of leca and pon geek out on getting their fertiliser right (don't worry, it's easier than you think these days).
Semi-hydro substrates provide little to no natural pH buffering compared vs soil, bark, spagmoss and other substrates. That does NOT mean you suddenly need to start testing and adjusting your pH (but you might want to embrace your inner plant scientist).
Depending partly on your water, partly on fertiliser, you may not have to worry yourself about pH when you shift to semi-hydro but - as well as changing your fertiliser - testing and adjusting the pH of your nutrient solution might be another possible change to expect compared to what you do now.
Most houseplant fertilisers are severely lacking when it comes to growing in semi-hydro substrates, leading to common issues like yellowing leaves from nutrient deficiencies.
Problems like yellowing and the 'one leaf club' (where you lose one leaf for every new leaf that grows), are often blamed on semi-hydro as a whole, which isn't fair, when really it could just be your fertiliser that's to blame.
More about the best fertiliser options and what to keep in mind around pH for semi-hydro both coming up.
Lesson #2: Pick the right plants
If you're new to semi-hydro, don't do what I did and learn on alocasia. Or on your favourite plant.
Or by all means do - you do you - but know that the higher maintenance the plant, the higher the risk of things not going to plan when both you and your plant are new to semi-hydro.
That's especially true for plants that dislike their roots being disturbed (like alocasia!). Expect a bit of adjustment ahead (for you and your plants).
TIP: The best plants to start with for semi-hydro
If I could start again, I'd do my semi-hydro learning on hardier plants. My top plant picks would be:
Pothos
A glossy-leafed, mainly-green Philodendron variety like a Brasil or Heartleaf
Peace Lily
Monstera deliciosa,
Syngonium,
Aglaonema.
Lesson #3: Slow down
Another big learning lesson is to take things slowly. Resist the urge to change ALL your plants over to semi-hydro ALL at once. Give yourself time to adjust your habits and routine, and to keep a close eye on each plant as it transitions.
Lesson #4: Self-watering doesn't mean 'wet and forget'
Yes, self-watering pots absolutely do REDUCE maintenance, especially handy for both under- and over-waterers (I'm in the second group myself). But they are NOT maintenance-free, so you can't just fill up the water reservoir and walk away.
You still need to regularly check root health, check the water level and water quality, and give everything an occasional flush-through and clean out.
Lesson #5: Leca and pon are not a magic wand
You won't magically be pest-free forever or never have root rot again. Although done right, I find the risk is lower for both*
*Depending on the pest of course, the risk is lower for for soil pests like fungus gnats and root mealy, but I haven't found semi-hydro changes the risk of foliage pests.
Your fussier plants won't magically thrive when they failed in potting mix. But for some the secret to growing them successfully when all else fails might turn out to be semi-hydro (a lot of alocasia hobbyists have found semi-hydro made all the difference).
And semi-hydro like leca and pon simply won't work for everyone. Like anything with plant care, it's a combo of what's best for your plant, for your plant-parent-style and your conditions.
Speaking of conditions, semi-hydro can't fix problems with the essentials. Light, temperature, air, humidity, nutrients... those still matter just as much (sometimes more).
Lesson #6. Leca and Pon are not the same
If a plant fails in leca, that doesn't rule out pon, and vice versa. Some plants simply do better in one vs the other. If you've tried one and been put off, don't give up on semi-hydro altogether.
As a general rule, I typically choose leca or a larger size of Pon for my chunkier, thicker-rooted plants like Monstera, Anthurium, Pothos, Philodendrons, Snake Plants, ZZ's and my larger Hoyas.
I prefer Pon in general, or a finer grade of Pon, for my finer-rooted plant friends like Alocasia, Anthurium, Calathea, Maranta, Begonias, Peperomia, African violets and my smaller Hoyas.
When to use Leca vs Pon?
I find Leca better for airflow, easier to keep an eye on roots, and more difficult to over-water once the plant's established.
The larger air gaps is also a downside for smaller or more delicate, finer roots. Leca can also be more prone to drying out too fast while a plant adapts and benefits from more frequent flushing than Pon.
Pon, typically a mix of pumice, lava rock (scoria), and zeolite, I find better for wicking moisture with better capillary action, making it my preferred choice for finer roots, younger root systems and more delicate roots. That property is also why plants generally transition easier to Pon vs to Leca.
Pon does have the downside of being a fair bit heavier. Being more expensive and smaller than Leca also tends to cost more to fill a pot vs Leca. Being smaller it's also harder to monitor roots in Pon vs Leca.
Lesson #7. Root melt is normal
Soil roots and water roots are NOT different types of roots, just adaptations. When roots go from one substrate to another they need time to adapt. Just being repotted is a HUGE change for most plants, which can send them into transplant shock.
The change from potting mix to semi-hydro can be a lot harder for a plant to cope with. Soil roots are not adapted to getting oxygen from water.
Some will slowly adapt, turning into water roots, without dying off in the process; but I'd consider it completely normal for soil roots to rot away during the transition, called root melt, in the process of growing new roots adapted to semi-hydro.
Good signs roots are tansitioning well is seeing new root tips, new white water roots growing, leaves and stems stay firm without wilting, no yellowing leaves, and seeing the water level going down as the roots use it.
To help with the transition, first make sure ALL the soil is washed off roots and trim away any damaged roots (more about prep steps coming up).
Then - even if you are doing the submerged method - keep the water level below the roots (more about wick watering vs the submerged method coming up too).
Pick a good fertiliser made for semi-hydro and always offer a nutrient solution (fertiliser + water), never just plain water (yes, more about fertiliser coming up below too).
Lesson #8. There are no 'rules'
You will find most semi-hydro fans recommend the same musts, but there really isn't one right way to do semi-hydro. Most agree but have found their own tips and tricks, like I'm sharing below, so start following the advice of someone more experienced that you, sure, but don't be afraid to experiment, and always use your plant's health as your guide.
The all-important prep BEFORE switching to semi-hydro
I found how you prep and switch can make or break your success with semi-hydro. Here's what I do...
Prep step 1 > Before you start
Firstly, pick the right time. As a general rule, switch during growing season. Think spring and summer. Plenty of light, nice and warm.
The right conditions helps roots adapt to semi-hydro much faster, reducing the risk of transplant shock. It is all about the roots at this stage.
Prep step 2 > Wash the roots
Next, get picky. Or rather, get washy. You want to get every bit of soil off those roots as best you can.
I like to give the plant a good soak a day or two before I plan to make the switch. That helps soften roots so they are more bendy and less likely to break when being handled, and helps loosen the old substrate out of all those nooks and crannies.
Once unpotted, gently shake off what you can then get washing. Don't pull on the rots. Soak or rinse the roots gently but thoroughly. Be patient with this step.
I use lukewarm water to avoid temperature shock. You can use running water (not too strong), a hose on the gentle spray setting, or a hand sprayer to help wet and loosen stuck bits.
Any soil you miss now can later increase the risk of rot, hold too much water and not enough air, and introduce nasties like bad bacteria and fungi.
Prep step 3 > Trim the roots
Last step before potting up is getting up close and personal. Take a good close look and gentle feel of the now clean roots.
Cut off anything that feels or looks dodgy. Soft, mushy roots need to go. Dried up, dead roots should be trimmed off too. Any roots that broke during prep are best chopped off also.
Prep your Leca or Pon too
Leca and Pon tends to come to you dry and dirty. A thorough rinse is important before you first use it. I would never pot up into dry leca or pon as it can be so good at wicking up moisture that it can suck your plant's roots dry!
I like to keep all that dirt and dust out of my sink so I head outside for the next step. I put the amount of leca or pon I need in a bucket and run the hose into it outside, letting the dust and dirt wash over the edge out onto the grass, until the water runs clear.
If I'm feeling impatient, I stop here and finish with a nutrient soak (a good soak in fertiliser and water), but ideally I'd tip out the dirty water and do another thorough rinse, then a nutrient soak, before I pot up.
What to do when root melt happens
If you do see signs of root melt or yellowing and leaf loss, don't panic. If it's only been a week or two, give the plant time to adjust.
At first, I normally flush and check the roots every fortnight. I like to add a little diluted hydrogen peroxide to kill off any bad bacteria or fungi and keep rot at bay. Remember that roots usually adapt first, before foliage improves.
Unless it's a matter of life or death, I'd give a newly transitioned plant around 4 weeks before making any further drastic changes.
The best fertiliser for semi-hydro
Okay, this one IS a biggie when it comes to semi-hydro. It's worth checking - and likely changing - what you feed. Make sure you shift plants to a fertiliser actually formulated for semi-hydro.
It should say in the product descrition if it's formulated for semi-hydro. Expect to see all 12 essential nutrients listed on the label. Look for a mention of whether it's already pH buffered (otherwise you'll likely need to start testing and adjusting pH every time you top up the water reservoir with fresh nutrient solution).
Three I'd confidently recommend are GT Focus, such as GT Foliage Focus, NurtureSystem No.1 PowerGrow and Superthrive, such as Foliage-Pro.
You absolutely can get your geek on and start testing electrical conductivity (EC) to check nutrient strength, shift to two or three part fertilisers, as well as testing and balancing pH; but having spent far too much time worrying about nutrients than I do now, without seeing much difference in my plant's health and growth; I'd keep things simple and pick a great single-part fertiliser that takes care of most of that for you.
The long method (a favourite for Leca)
If you've tried and failed with semi-hydro before, or you really don't want to lose the plant, or you just don't want to take any risks (or as few as you can control anyway), absolutely go for the long method.
This is a method you'll see The Leca Queen suggest. I highly recommend looking up her YouTube channel for all thing Leca (she's fantastic, do yourself a favour and binge watch her content before you first try Leca, it'll save you dealing with so many problems).
Instead of going from soil or potting mix to leca, or potting mix to pon, the long method adds a step in-between.
Still prep the plant like outlined above, but now shift the plant to nutrient water. Wait to see new growth of those whiter, finer, water-adapted roots. THEN shift to Leca or Pon.
I've used the long method many times and prefer it when shifting to Leca. With Pon I'll usually go straight from soil to Pon provided excellent prep, but again, would suggest the long method either way if you're new to semi-hydro.
What type of wick material and thickness is best for self-watering?
Most self-watering pots or kits come with cotton wicks. These tend to do a fantastic job wicking water up from the reservoir into the substrate BUT won't last forever.
You may like to swap to a synthetic wick later, or start with synthetic from the beginning. I usually swap for synthetic from the start as wicks can be a pain to change later and I'd rather not introduce rot even if it takes a long time.
You have lots of wick options. Acrylic yarn is a good cotton alternative. It won't rot like cotton eventually can, and also fully absorbs water to its core, so wicks really well. Natural yarn like wool has the same issue as cotton over time so I'd avoid wool yarn.
If cotton or acrylic yarn wicks too much water or your substrate's staying too wet, another option is a braided nylon cord. I'd start with a minimum of 2mm thick with 3mm to 6mm being popular options.
Also called Mason Line, braided nylon cord tends to shift water well but not absorb it right to the core, so doesn't wick up as much water as acrylic or cotton.
Polyester cord or paracord are another option for a happy medium between acrylic yarn and cotton wicks, vs nylon cord at the other end of the scale.
A popular synthetic wick solution specifically for Leca (but which absolutely works a treat in Pon also), is microfibre strips. The easiest source for this a microfibre mop head (a trick I learned from The Leca Queen).
Mason Line and braided nylon cord you should find easily at your local hardware store like Mitre 10 or Bunnings. Acrylic yarn should be easy to find at a hobby store like Spotlight.
ABOUT THE AUTHOR: Anna is the owner of plant store Love That Leaf which specialises in products and advice for indoor plants. She is also the resident indoor plants writer for NZ Gardener magazine. Her houseplant care articles appear in print in magazines in-stores NZ-wide, and online on Stuff, The Post, NineHoney and more.