Cover has to work at the surface, not just the bottom
Newly born and newly hatched fry are hunted from above and below, and different species instinctively head for different levels. Livebearer fry such as guppies rise to the surface within moments of birth, so floating plants are their first lifeline: water lettuce, salvinia or even a raft of loose plant trimmings dim the light, break the surface into shadow, and give tiny fry a ceiling of roots to hide among. A bare tank with one plant in the corner leaves the surface wide open, and that is where most fry are lost in the first day.
Moss and fine-leaved tangles are the mid-water refuge
Java moss is the classic fry plant because its structure is exactly fry-sized: a loose, springy mass full of gaps a newborn can slip into and an adult mouth cannot follow. Guppy grass does the same job faster, growing into a soft thicket within weeks, and fine-leaved stem plants left untrimmed give similar cover. Let the tangle grow dense rather than sculpting it — a golf-ball clump of moss protects nobody, while a mass filling a third of the tank shelters a whole brood. Anchor moss to wood or stone so it stays put when you siphon around it.
The plants are also the pantry
The least obvious benefit of a planted grow-out tank is that it feeds the fry between your feeds. Every plant surface grows biofilm — a living layer of microorganisms — and among it thrive infusoria, the microscopic animals that are the perfect first food for fry too small for powdered food or baby brine shrimp. Fry in a mature planted tank graze constantly, pecking at moss and leaf surfaces, which is why broods raised in old, planted tanks often outgrow those in sterile bare ones. A handful of dried leaf litter on the bottom boosts this effect, slowly fuelling the micro-life fry pick through.
Low leaves and shadow for the shy species
Not all fry come to the surface. Egg-scatterers' fry and shy species hug the bottom and the shade, so give them broad low leaves — anubias or cryptocoryne planted near the substrate — and a piece of wood or a coconut cave that makes a dark overhang. Layering the tank this way, floaters above, moss in the middle, broad leaves below, means every fry finds the level it instinctively wants, and no layer is crowded. Keep a gentle sponge filter running so the water stays clear without a current strong enough to exhaust small swimmers or suck them in.
Set the plants up before the fry arrive
A planted nursery works best when it is not brand new. Set the tank up a few weeks ahead if you can, let the moss establish and the biofilm build, and keep lighting on a steady daily rhythm so the plants grow rather than melt. Snails that hitchhike in on plants are harmless grazing companions at this scale and help keep surfaces clean. When a plant on your shortlist looks wrong for fry cover, put a follow-up question to KinsLe’s Kinny; he answers using the KinsLe Answers library.