Citrus & Mediterranean Pack: Or Brun Soil 20 L + Biochar & Mycorrhizae

A citrus or olive tree in a pot is not a houseplant: it is a woody shrub, which will live for years in the same container and is only repotted once every two or three years. What goes into the pot on repotting day must therefore last a long time — and meet a contradictory requirement.

The paradox of the potted lemon tree

These plants fear stagnant water more than drought: roots that sit in water rot, and it is the first cause of loss of a citrus in a tub. They therefore need a draining substrate. But a substrate that drains well also lets part of the water and nutrients you have just supplied escape at every watering. Draining and retaining are two opposite requirements, and that is exactly what the two products in this pack share between them.

The potting soil: draining, thanks to pozzolana

The Or Brun Citrus & Mediterranean Plants Potting Soil contains pozzolana, a porous volcanic rock that keeps pathways open for air and water at the heart of the root ball. Around it, a blend of blond peat, composted bark, wood fibre, green compost and horse manure with seaweed. It is certified growing medium NF U 44-551, its pH is 6.9 — the range in which citrus assimilate best — and its water retention capacity is measured at 545 mL/L. It carries an NPK 7-4-7 fertiliser dosed at 2 kg per m³, in accordance with standard NF U 42-001-3.

The fertiliser: retaining, and reaching out

The 500 g of Terra Fertilis granules do the opposite job, and they do it in two ways. The biochar, a porous and stable plant charcoal, retains water and fertilising elements instead of letting them run out through the drainage hole, then releases them gradually — it does not decompose and stays in the substrate from one repotting to the next. The mycorrhizae (Glomus deserticola) do something else: these fungi colonise the roots and extend their network with much finer filaments, which increases the exchange surface with the soil and gives access to water and nutrients that the root alone would not reach. The product is usable in organic farming, with no chemical additive.

The right move, at repotting

It is at repotting that this pack makes the most sense, because the mycorrhizae must touch the roots to settle there. Take the shrub out of its pot and gently loosen the old substrate around the edge of the root ball. Pour a layer of potting soil at the bottom of the new tub, set the root ball down, then mix the granules into the backfill potting soil, as close to the roots as possible, filling the gaps. Firm lightly and water generously. For a plant already in place that you do not want to disturb, the granules are applied by scratching them in beneath the crown.

What the pack contains