How to Feed QuadGrow Planters – What I’ve Learned (And What to Avoid)

If you’re wondering how to feed QuadGrow planters when the tank isn’t empty, you’re not alone. It’s one of the most common questions I get – and once you know how, it’s surprisingly simple. In this post, I’ll share how I do it, what fertilisers work best, and the big mistake that took me three growing seasons to fix.

So, if you’re using a QuadGrow self-watering planter and aren’t sure how to top up the feed mid-season, grab a cup of tea – I’ll walk you through it.

What Is a QuadGrow Planter and How Does It Work?

The QuadGrow is a self-watering planter system that uses a reservoir and capillary mats to deliver water and nutrients to your plants as they need them. I’ve used them for years in my greenhouse to grow tomatoes, peppers, and aubergines, and they’ve been brilliant for cutting down on watering stress, especially in warm spells.

Each planter holds four pots, with the water and feed sitting in the reservoir below. Your plants draw up moisture via capillary matting that’s fed through the pots into the reservoir underneath, so they’re never waterlogged but never dry out either.

Feeding QuadGrow Planters – My Topping Up Method

Here’s the bit most people get stuck on: how do you top up feed without emptying the tank?

The good news is – you don’t need to empty anything. You just treat the water you’re adding.

Here’s what I do:

Figure out how much water you’re adding – for example, 5 litres.
Mix your feed in a watering can, based on that amount. If I’m using Nutrigold (the feed that comes with the QuadGrow), I use:
- 6ml of part A and 6ml of part B per litre of water.
- For 5 litres, that’s 30ml of each.
Give it a good stir or shake, then pour it into the reservoir up to the usual fill line.

That’s it. You’re not treating the full tank volume – just the water you’re adding in that moment. Makes life much easier!

Can You Use Other Liquid Fertilisers in a QuadGrow?

Yes, absolutely. Once I’ve used up the Nutrigold that comes with the system, I often switch to a regular tomato feed like Tomorite, or even supermarket own-brand ones. The QuadGrow doesn’t need anything fancy – just something that dissolves fully in water and won’t clog up the system. Although it’s worth noting that the Nutrigold is top notch stuff and will be way better than random off the shelf stuff.

Just one golden rule: follow the instructions on the label of whatever feed you’re using. Don’t just copy the Nutrigold measurements – every fertiliser has its own dilution rate.

If it’s a liquid tomato feed, chances are it’ll work just fine. I’ve used them for years with no issues.

What Feeds to Avoid (Please Learn from My Mistake)

Now for the cautionary tale. A few years back, I used a seaweed feed in my QuadGrow. It was organic, homemade, and seemed like a great idea at the time.

But organic feeds – especially things like seaweed or comfrey tea – are full of live bacteria, yeast, and microbes. And when you add them to a dark reservoir sitting in a warm greenhouse, you’re basically creating a fermenting soup.

The result? A stinky, slimy mess that absolutely ruined my plants – and worse, it lingered. Even after bleaching the tank, the smell and problems came back the following year. It actually took me three full seasons to get rid of it completely.

So now I avoid:

Seaweed extract
Comfrey tea
Anything that needs to be stored in a fridge or “used within X days”

If the feed is alive, don’t use it in a QuadGrow. Stick to shelf-stable, fully soluble fertilisers and you’ll save yourself a lot of trouble.

Want to See the Process?

I’ve got a quick video where I show you how I top up feed in my own QuadGrow units – and what to avoid!

Final Thoughts

Feeding QuadGrow planters doesn’t need to be complicated. Once you know how to treat the water you’re adding – and which fertilisers are safe – it becomes just another easy garden routine.

I hope this post clears up a few questions if you’ve been scratching your head. And if you’ve got a favourite liquid feed that works really well in your system, let me know in the comments – I’m always curious to try new things.