Tool
Desiccant amount calculator
How much silica gel to tuck into a seed jar so the seed stays dry.
Your result
About 10 g of silica gel
- Container volume (litres)
- Seed condition
A sensible range for this jar is about 5–15 g. More is not harmful; it simply saturates more slowly.
What this calculator does
Silica gel is a desiccant: it absorbs water vapour from the air around it. Sealed in a jar with dry seed, it mops up stray moisture and helps keep the seed in the low-humidity conditions that make it last. This tool estimates a sensible amount from the size of your container, using a rough rule of about 10 g per litre for dry seed, rising to around 20 g per litre if conditions are damp or the seed is not fully dried. It is an estimate — there is no harm in using more.
When to use it
- Putting saved seed into jars for storage.
- Rescuing seed stored in a humid room.
- Switching from open packets to a sealed seed box.
How to use it
- Dry the seed first. Silica gel maintains dryness; it cannot dry wet seed. Air-dry fully before sealing.
- Measure your jar. A rough volume is fine — a jam jar is usually around half a litre.
- Choose the condition and read the amount.
- Seal the jar and check the gel now and then, recharging or replacing it when spent.
Worked example
A one-litre jar of fully dried bean seed, stored in a normal room, wants roughly 10 g of silica gel — an amount that often comes as one or two small sachets. If the room is humid or the seed is only just dry, aim nearer 20 g and recharge sooner.
Why dry seed keeps longer
Moisture is one of the two great enemies of stored seed, along with heat. Damp seed ages faster, can start to germinate in the packet, and grows mould. Keeping the air in the jar dry slows all of that down, which is why seed banks store seed cold and dry. A sealed jar with a little silica gel is the simple home version.
Limitations
- Silica gel saturates. It has a limit; once full, it stops helping until it is dried out again.
- It is not a substitute for drying. Sealing seed that is still damp, with or without gel, invites mould.
- Use food-grade sachets. Do not use the tiny non-food sachets that come with electronics.
Frequently asked questions
Can I reuse silica gel?
Often yes. Many types can be dried out in a low oven and used again — check the product. If in doubt, replace it.
How do I know when it is spent?
Some types change colour when saturated. Otherwise, replace it after a season, or if the seed shows any sign of damp.
Does the gel touch the seed?
Keep it in its sachet rather than loose, so seed is not in direct contact. In a sealed jar the gel dehumidifies the whole space anyway.
Related guides
Sources and research notes
Amounts are a rough home-garden guide based on the principle that dry, sealed storage keeps seed viable longest; exact needs depend on the seed and the room.