The first rule with seeds is to use as fresh as possible.
That’s not to say that you need to throw out last years leftovers, but you do need to consider how you’ve stored them in between.
Seed packs, even unopened ones left in the greenhouse during the raging heat of summer and the bitter cold of winter are likely to be compromised.
Open packets that have been allowed to become damp are unlikely to grow.
Many seeds will last more than adequately from season to season if kept in cool, dry and dark storage somewhere in the home. In fact a fair few will last for decades like this, while others such as parsnip seed, really needs to be sown and grown fresh each season.
I am always amazed at people that simply dig up a trowel full of garden soil and use that to grow seed. It may be OK for a few garden stalwarts but if you plan to grow in a greenhouse or want to grow any delicate or expensive seed then it’s really not a good idea.
The soil contains billions of microbes, which are all in balance in the garden and merge together to create a happy and healthy outdoor environment.
But ship this soil into the greenhouse and one or more microbes will overpower the others resulting in a soil borne pest or disease problem that will love your new sown plants.
It’s not scaremongering, it’s common sense.
For the sake of the cost of a small bag of seed compost, it’s really not worth the risk, especially with the price of some seeds.
A 20l bag will be enough for dozens of small pots of seeds and cost about the same as a pack of seed.
To save money buy a large bag between gardening friends and split it into equal portions. Buy good quality seed compost that is fresh into the garden centre and don’t cut corners. Then a few days before you start sowing, bring the compost into the greenhouse to acclimatise. It’s nicer for you to get your hands into warm compost and it’s better for the seeds, avoiding cold shock and damp issues.
Use clean flowerpots, seed trays and modules. Reuse last years, just give them a good clean out before use. Wash them with a good greenhouse cleaner or some hot soapy water, there’s no need to use bleach or other aggressive cleaners, but it’s important to start with clean pots. Fill them with good clean fresh seed compost and when it’s time to water your seeds, use tepid tap water until your plants are mature and established.
You may still have the odd failure but your successes will outweigh them every time and if something doesn’t grow, don’t assume it’s your fault, just start again, following the rules and just a couple of weeks may make all the difference to your plants survival.