How to clean seed trays and propagators between batches

Illustration of a covered electric propagator containing seed pots on an indoor windowsill

Affiliate disclosure: As an Amazon Associate I earn from qualifying purchases. This article contains affiliate links.

Cleaning seed trays and propagators between batches is not just about tidiness. Damping-off fungi and fungus-like organisms such as Pythium, Phytophthora, Rhizoctonia and Fusarium can survive on used trays, pots and propagator surfaces, ready to infect the next sowing. The RHS advises that if you must reuse trays, you should brush off soil, wash them and preferably treat them with a garden disinfectant, then dry before storage. This article sets out a practical cleaning routine for seed trays and propagators between sowings, including when warm soapy water is enough and when a disinfectant is worth the extra step.

Table of Contents

Why cleaning between batches matters

Damping off is a disease of seedlings caused by several soil-borne fungi and fungus-like organisms. It is particularly a problem when sowing seed indoors or under glass, where high humidity and poor air circulation favour the pathogens. The organisms can persist on dead plant material and on surfaces in greenhouses and on tools, so reusing dirty trays or propagators can carry infection from one batch to the next. No fungicides are available to gardeners for controlling damping off, which makes physical cleaning and hygiene the main line of defence.

What you will need

Warm water
A small amount of mild detergent or washing-up liquid
A stiff-bristled scrubbing brush
A plastic plant label or flexible scraper for dislodging dried compost
A garden disinfectant labelled for the intended horticultural equipment (optional, for disease prevention)
Rubber gloves
Clean cloths or a drying rack

Separate electrical parts before cleaning

Switch off and unplug a heated propagator, heat mat or controller before cleaning. Only removable non-electrical trays and lids should enter a bucket or sink when their instructions permit it. Never immerse a heated base, thermostat, plug or electrical connection. Clean electrical parts only by the maker’s method and allow them to dry fully before reconnecting.

Step-by-step cleaning method

Remove all compost and plant debris. Use a stiff brush or an old plastic plant label to scrape dried compost out of tray cells, corners and crevices. Do this outdoors or over a bin so that spores and debris are not spread around the greenhouse or shed.
Wash in warm soapy water. Fill a bucket or sink with warm water and a small amount of mild detergent. Scrub every surface, including the underside of trays, the inside of propagator lids, vents and any joins where debris collects. Pay particular attention to the gaps between slats on staging if you are cleaning that too, but the focus here is on trays and propagators.
Rinse thoroughly. Use clean water to remove all detergent and loosened dirt. Any residue left behind can reduce the effectiveness of a later disinfectant step.
Disinfect if appropriate. For appropriate reusable equipment from healthy batches, treat the cleaned removable trays and propagator parts with a garden disinfectant labelled for the intended horticultural equipment. Always follow the manufacturer’s instructions for dilution, contact time and safety precautions. Do not skip the washing step: disinfectants work best on clean surfaces, and organic matter can shield pathogens.
Rinse again if required, then dry completely. Some disinfectants need a final rinse; check the label. Air dry on a clean rack or wipe with a clean cloth. Make sure no moisture remains in crevices or under rims before storage, because damp conditions encourage mould and bacterial growth.

Equipment after a damping-off outbreak

Follow the RHS precaution not to reuse affected pots and trays for raising vulnerable seedlings. Keep them and suspect compost away from clean equipment, and start replacement batches with fresh compost and suitable clean containers. A general washing or disinfecting routine cannot guarantee that an affected tray is safe for the next sowing.

When warm soapy water is enough

For routine cleaning between healthy batches, warm soapy water and thorough scrubbing may be sufficient. The RHS greenhouse cleaning guide notes that warm water is generally sufficient to make surfaces clean, and that propagation equipment and pots can be cleaned in warm soapy water. If you have had no disease problems and the trays are only lightly soiled, a good wash and rinse followed by drying is a reasonable approach. If unexplained seedling collapse occurred, investigate the cause and follow the affected-equipment precautions above rather than assuming washing or disinfectant has resolved it.

Disposing of diseased seedlings and compost

If a batch of seedlings has damped off, do not put the collapsed seedlings or the compost from those trays into your home compost bin. Home compost bins rarely reach temperatures sufficient to kill damping-off pathogens. The RHS advises that rotten bulbs, collapsed seedlings in contaminated compost and similar material can be thrown away in household waste where the local service permits it. Council green waste collections may also accept diseased material if the composting facility reaches high temperatures, but check with your local authority first. This prevents reintroducing the pathogens when you later use your own compost.

Drying and storage

After cleaning, dry trays and propagator parts completely before storing them. Stacking damp trays encourages mould and can leave water trapped between nested cells. Store clean, dry trays in a clean, dry place such as a shed shelf or greenhouse staging, ideally covered or upside down to keep dust and debris out. Before the next use, give trays a quick visual check and a wipe with a dry cloth if they have gathered any dust.

Useful product types

Two product types can be useful for this job. A garden disinfectant labelled for the intended horticultural equipment can reduce damping-off pathogens on cleaned surfaces, but it is not a substitute for washing. Check the label for suitability on plastic, required dilution, contact time and whether a final rinse is needed. A stiff-bristled scrubbing brush with a long handle helps reach into tray cells and propagator corners. Choose one with bristles firm enough to dislodge dried compost but not so hard that they scratch the plastic, as scratches can harbour pathogens.

Useful products for this job

The links below open Amazon UK product searches. Check the exact item, seller, current price and compatibility before buying.

Horticultural equipment disinfectant: May be appropriate after washing equipment when the label covers the intended surface and use. Check label for suitability on plastic, required dilution, contact time, and whether rinsing is needed after use. Search Amazon for Horticultural equipment disinfectant.
Stiff-bristled scrubbing brush: Removes dried compost and debris from tray cells and propagator corners before washing. Choose a brush with bristles firm enough to dislodge soil but not so hard it scratches plastic; a long handle helps reach into cells. Search Amazon for Stiff-bristled scrubbing brush.

Related garden guides

Sources and further guidance

Guidance researched in September 2026. The feature image is an AI-generated illustration. Product guidance is based on published information, not hands-on testing.