Coco coir for beginners: buffering, watering and cal-mag

Coco is the easiest media to get good results in and the easiest to get confusing results in, and it is the same property causing both. Unlike inert media, coco takes an active part in your feeding.

What coco actually is

Coco coir is the fibrous husk of a coconut, washed, aged and graded. It holds water like a sponge while staying full of air, which is the combination every root system wants. It is also a renewable by-product of an existing industry, which is a nicer story than peat has.

You will see it sold as straight coco, as a coco and perlite blend, and as compressed bricks. We stock 53 litre loose-fill bags of both straight coco and a 70/30 coco perlite mix, because loose fill saves you the least enjoyable hour in growing -- rehydrating bricks in a wheelbarrow.

The thing that matters: cation exchange

Coco has a high cation exchange capacity. In plain terms, the fibres have sites on them that hold positively charged nutrient ions, and those sites will swap what they are holding for whatever is in the solution around them.

Raw coco arrives with those sites loaded up with potassium and sodium. When you water it with your nice balanced feed, the coco grabs calcium and magnesium out of your solution and releases potassium and sodium in exchange. Your plant gets a feed that is nothing like the one you mixed, and you get calcium and magnesium deficiencies in week two while swearing the chart says there is plenty in there.

Buffering is the process of pre-loading those sites with calcium and magnesium before you plant, so the coco is already full and stops stealing.

Buffered, washed and RHP

Good quality coco has been washed to remove salts and pre-buffered at the factory. Look for RHP certification -- it is a Dutch horticultural standard that covers washing, buffering and consistency, and it is the shortcut to not having to think about any of this. Both of our Green Planet 53 litre bags are RHP certified.

If you have unbuffered or unknown coco, buffer it yourself: soak it thoroughly in a strong cal-mag solution, around EC 2.0, leave it a few hours, then rinse with pH-adjusted water until runoff EC is close to what you put in.

Cal-mag is not optional

Even in buffered coco, run a calcium and magnesium supplement through the whole cycle. The exchange sites keep working, your plant keeps drawing calcium, and coco does not have a reserve to draw on the way soil does.

Rainwater and RO water make this more important, not less -- there is no calcium in either to begin with. Brisbane tap water carries some hardness, but not enough to rely on. Test yours rather than assuming.

Watering: little and often

The instinct from soil is to water heavily and then leave it. Coco wants the opposite.

Coco holds a lot of water but it also holds a lot of air, and the roots will happily take frequent watering without drowning. Frequent small waterings keep the moisture and the nutrient concentration steady, which is exactly what you want. Long dry-back cycles let salts concentrate as the water evaporates, and the plant gets a stronger and stronger feed as the pot dries.

A reasonable starting point is several short irrigations across the light period rather than one big one, with enough volume each time to get 10 to 20 percent runoff. Runoff is not waste -- it is what stops salts building up, and it gives you something to measure.

This is precisely the job an irrigation system does better than a person with a watering can. If you are running more than a handful of pots, a whip line kit turns three waterings a day from a chore into a timer setting.

pH and EC in coco

Aim for pH 5.5 to 6.2 going in. Coco has some buffering capacity of its own but nothing like soil, so it is worth adjusting properly rather than hoping.

Watch runoff EC weekly. Climbing steadily means salts are accumulating -- water to more runoff, or ease the feed strength back. Sitting well below your input means the plant is eating everything you give it and you have headroom.

Straight coco or coco perlite

Straight coco holds more water and is more forgiving of a missed watering. It suits hand watering, bigger pots and cooler rooms.

A 70/30 coco perlite blend drains faster and holds more air, which suits frequent automated irrigation, smaller pots, and Brisbane summers where a wet pot in a warm room is asking for root problems. If you are on a timer, the blend is usually the better call.

Common mistakes

• Treating it like soil. Watering once every few days and skipping runoff is the fastest way to a salt problem.
• Skipping cal-mag because the base nutrient says it is complete. Coco-specific base nutrients account for this; generic ones often do not.
• Using unwashed cheap coco and fighting sodium all cycle. The bag saves you fifteen dollars and costs you a crop.
• Letting it dry out completely. Coco is very hard to rewet evenly once it has properly dried -- water runs down the sides of the pot and straight out the bottom.

Both our 53 litre bags are $45 and in stock at the shop on Ipswich Road. Come and squeeze a handful before you buy a pallet of it.