Pests in Greenhouse

[carly]

It's up to you. Personally I re-use all my old compost but always start seeds off in fresh stuff just in case there are any nasties overwintering in it. The fungus gnats don't seem to care, they hang around both.

Ok, I have just put all old compost and soil into a big wide plastic thing and moved it all around. It’s 76 in the greenhouse at the moment so it should dry off the moist stuff. I have started my seedlings with fresh stuff. Have you ever had any damage to seedlings from gnats?

[Jungle Jane]

Flies lay eggs in my soil outside (no greenhouse) & overwinter then fly about but I don’t remove any soil,no plants here have suffered because of flies except for large numbers of black flies & whiteflies but you can deal with infestations when you see them so it doesn’t get to the damaging stage,like when I had fungus gnats indoors with some plants,if you let the pot dry out a bit & water from below,squash what you see you can manage them. It’s impossible to get rid of flies totally,you could try some garlic sprayed around near your seedlings so they don’t want to go near them maybe but I’d probably just not worry unless there’s about fifty living & flying around the seed tray,then deal with that when it happens & you can deal with them it’s mostly just annoying. I always water everything from below now to keep the top of the compost dry then they can’t lay their eggs in it.

[muck lover]

Try the Roman approach.
I squishum
I squirtum

[Aberdeenplotter]

Marigolds maybe?

French Marigolds for sure. I plant 3 of 4 in each bucket I grow my tomatoes in and haven't had a problem with whitefly since I started doing so.

[Jane0o0]

Can you have Marigolds in separate pots just standing on the grow bag next to tomato plants. Is that ok? Its my first year of gardening ever, whether it be in greenhouse or garden so don't know much though I'm learning.

[Aberdeenplotter]

no reason why not. Only downside I can think of is having to water the marigolds separately.

On subject of watering, and I'm only putting this forward because you are a self confessed novice, it's important with tomatoes to water regularly keeping them moist (as opposed to wet). Irregular watering can lead to a condition known as blossom end rot. A blackened area develops at the base of the fruit. I discard any that develop like that but it's said that the blackened bits can just be cut off and what remains is edible.