Most spider mites survive without plants for just 2-5 days under normal home conditions. They need plant sap to live and breed. Without a host they dry out and die fairly fast. But some can hide and wait much longer if you give them the right conditions to survive.
I cleared out my sun room after a bad mite outbreak hit my whole plant shelf last spring. I moved all my plants out and waited ten days before putting anything back in. That wait time worked well and I had no return of mites on my new plants after that break.
The spider mite lifespan without host gets longer when you keep temps low in your space. Cool air slows their body functions way down to almost nothing. Female mites can enter a sleep state that lets them live for weeks or even months in your home. They hide in cracks, soil, and dead leaves waiting for spring warmth to wake them up.
Dry air shortens survival time since mites lose water fast through their thin skin. A room you keep at 40% humidity kills most mites within two days or less. Damp spots above 60% let them hang on much longer than you might expect. Run a fan to dry things out if you want mites gone faster from your space.
You should watch out for spots where mites can hide and wait for your new plants to arrive. Window frames, shelf cracks, and pot rims all give them shelter from dry air. Soil from your old pots may hold sleeping mites too. Clean all these spots well before you bring any plants back into your space.
My second run in with this came when I reused pots too soon from plants I had thrown out. Mites had hidden in the rim grooves and woke up when I added new soil and plants. Now I always wash my pots in hot soapy water and let them dry in full sun before I use them again for anything.
For a safe wait time you should plan on at least one full week with no plants in your room. Two weeks is even better if you had a bad case to deal with. Keep your space dry and warm during this time to speed up mite death. You should wipe down all surfaces with damp cloths to remove any eggs or stragglers you cannot see.
The question of how long spider mites live off plants also depends on where you live. Cold winter areas see mites survive in garden debris until spring arrives in your yard. Mild climates let them stay active year round outdoors near your home. Indoor mites die faster since homes tend to be drier than outside air.
Before you bring plants back you should check your whole room with a bright light and hand lens. Look in corners, along edges, and under your shelves for any signs. Any webbing you see means mites may still be around waiting for food. Wait another week and clean again if you find any signs of life before your new plants go in.
Read the full article: Ultimate Spider Mite Control Guide
