Soil & potting mix
Best soil for Cobweb Spiderwort (Cyanotis arachnoidea)
Also called Cobweb Spiderwort, White Grass of the Dew, Grass of the Dew.
More about cobweb spiderwort
About Cobweb Spiderwort
Cyanotis arachnoidea · also called Cobweb Spiderwort, White Grass of the Dew · houseplant
Cyanotis arachnoidea is a creeping, softly hairy perennial from tropical Africa and Asia, bearing cobalt-blue or pink three-petalled flowers. Its prostrate stems root freely at nodes, making it an excellent groundcover or trailing basket plant. It needs bright light, well-draining soil, and warm, humid conditions.
Preferred mix: Moist, well-draining organic mix
Watch for — Root and stem rot: Overwatering or poor drainage causes soft, blackened stems at the base. Always use pots with drainage holes and allow the surface of the soil to dry slightly between waterings.
Why cobweb spiderwort needs this mix
Cobweb Spiderwort is an easy-going houseplant — it just wants a free-draining general mix that holds some moisture but never stays soggy.
- Cobweb Spiderwort is adaptable, but like most houseplants it still needs air at the roots — a mix that drains freely while holding a working moisture reserve.
- A little perlite or bark stops ordinary compost compacting into an airless block over time, which is the slow, common cause of decline.
- It is not fussy about pH or special ingredients; getting the air-to-moisture balance right is what matters.
For the full picture on what makes up a good mix, see our guide to the main types of soil and potting media — it explains why each ingredient above behaves the way it does.
What goes wrong with the wrong mix
The wrong soil is one of the most common reasons cobweb spiderwort struggles, and the damage often shows up weeks later as a watering problem. For this species specifically:
- Plain garden soil or a cheap, claggy compost compacts in the pot and slowly suffocates cobweb spiderwort's roots.
- A pure peat mix that dries to a hard, water-repelling block is hard to re-wet and stresses the plant.
- No drainage hole turns even a good mix into a stagnant, root-rotting sump.
Reusing tired, compacted old compost or skipping the perlite. A free-draining mix in a pot with a hole solves most "why is it struggling" cases for cobweb spiderwort.
pH — does it matter for cobweb spiderwort?
Cobweb Spiderwort is not fussy about pH — a slightly acidic to neutral mix (around pH 6.0-7.0), which a standard peat-free compost provides, is perfectly fine. No testing needed.
If you want to check or adjust it, the soil pH guide walks through testing and the safe ways to nudge a mix more acidic or more alkaline.
DIY mix vs a bagged one
A decent bagged houseplant compost works for cobweb spiderwort as long as you mix in perlite for air. The simple DIY ratio above is cheap and more reliable than a budget bag alone.
Drainage and the pot
A pot with a drainage hole and a saucer you empty after watering is all cobweb spiderwort needs — the free-draining mix does the rest.
Refresh cobweb spiderwort's mix every 18-24 months; even good compost slumps and compacts, and fresh, airy mix is often the simplest fix for a tired plant. When the time comes, our repotting guide for cobweb spiderwort covers the timing and technique step by step.
Cobweb Spiderwort soil — frequently asked questions
What is the best soil mix for cobweb spiderwort?
3 parts peat-free houseplant compost : 1 part perlite : 1 part orchid bark or coco chips (optional). Cobweb Spiderwort is adaptable, but like most houseplants it still needs air at the roots — a mix that drains freely while holding a working moisture reserve.
Can I use normal potting soil for cobweb spiderwort?
Plain garden soil or a cheap, claggy compost compacts in the pot and slowly suffocates cobweb spiderwort's roots. A decent bagged houseplant compost works for cobweb spiderwort as long as you mix in perlite for air. The simple DIY ratio above is cheap and more reliable than a budget bag alone.
Does cobweb spiderwort need a special pH?
Cobweb Spiderwort is not fussy about pH — a slightly acidic to neutral mix (around pH 6.0-7.0), which a standard peat-free compost provides, is perfectly fine. No testing needed.
Should I buy a bagged mix or make my own for cobweb spiderwort?
A decent bagged houseplant compost works for cobweb spiderwort as long as you mix in perlite for air. The simple DIY ratio above is cheap and more reliable than a budget bag alone.
How often should I refresh the soil for cobweb spiderwort?
Refresh cobweb spiderwort's mix every 18-24 months; even good compost slumps and compacts, and fresh, airy mix is often the simplest fix for a tired plant. A pot with a drainage hole and a saucer you empty after watering is all cobweb spiderwort needs — the free-draining mix does the rest.
Keep reading
- Cobweb Spiderwort care — the full brief (light, water, humidity, problems, pet safety)
- How often to water cobweb spiderwort — the schedule the mix feeds into
- Repotting cobweb spiderwort — when and how to refresh the mix
- Soil pH guide — test it and adjust it safely
- Should I water my plant? The simple check first
- Overwatered plant — signs and recovery
- Root rot — how the wrong soil starts it, and how to save the plant
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