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How to use a cold frame for seedlings / very young vegetable plants

WildFlower85WildFlower85 Cambridgeshire, UKPosts: 166
Last year we grew a small variety of vegetables and herbs from seed (just courgettes and basil - I also grew tumbler tomatoes but from shop-bought small plants, and Charlotte potatoes from seed potatoes). But this year I'm upping my game, installing new raised beds, and plan to grow a lot of variety:

- Tumbler tomatoes
- Courgette - yellow
- Courgette - Black Beauty
- Sweet Basil
- Russian Tarragon
- Coriander
- Lettuce mix - Red Salad Bowl, Suzan, Marvel Of Four Seasons, Little Leprechaun (to be sown straight into the ground)
- Wild rocket (to be sown straight into the ground)
- Tomato - Moneymaker
- Dwarf French Beans
- Radishes mixed (to be sown straight into the ground)
- Rainbow beetroot (to be sown straight into the ground)
- Chilli Pepper Padron

I have just about enough indoor window space with good light to grow these in seed trays, but as soon as they need to be grown on in larger 9cm+ pots, I think I'm going to struggle for bright indoor space. I want to end up with between 1-3 plants of each variety (minus the lettuce, rocket, radishes and beetroot which will be sown direct outside throughout the summer for a constant supply) and expect if each variety was in a 9-15cm pot, would be able to fit about half of them in the cold frame and keep the rest inside.

I guess my question is, can very young vegetable plants in 9cm+ pots go in a (south facing) cold frame? If I start sowing in Feb-April and can't plant out in their final beds/pots until mid-June, there will be some time in April and May where I hope to have some of the plants in the cold frame, but not in a hardening off kind of way as they'd still be quite young.

Any advice would be helpful!
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  • FairygirlFairygirl west central ScotlandPosts: 35,520
    A cold frame is essentially a small greenhouse, so yes - you can put plants out in it, assuming weather/temps are suitable. That's the key factor when you want to put plants that have been in a warm house, out into the big outdoors. 
    Ideally, you would put them in it with the lid open through the day according to weather, and close it at night, but its really about timing it with temps. It can get very hot inside a cold frame, even at that time of year, and then you can have a sharp drop. Fluctuation is worse for plants than a steady, cooler temp. 
    Hardier plants will cope quite quickly. Basil wouldn't survive in a cold frame here at that time of year - I don't sow it until April, so again, it's about your own conditions.
    Tomatoes get sown late March for the same reason, and really have to be grown inside, so mine have to wait. 
    I think if you stagger your sowings too, that will make life easier. Just keep some plants back if you're not going to have room once they're potted on, and work out what room you have in the frame. A bit of juggling is always required when space is limited ;)
     
    Your list is a bit confusing as there are plants that aren't going in the frame though.

    Once you have wild rocket, you'll always have it. Brilliant stuff  :)  
    It's a place where beautiful isn't enough of a word....


  • WildFlower85WildFlower85 Cambridgeshire, UKPosts: 166
    Thanks @Fairygirl, that's all very helpful. I only included the sown outside veg as I copied it from a record I'm keeping, but I can see how it's confusing!

    Sounds like I can maybe choose the hardier and later sown plants to go in the cold frame from late April/May depending on the temp, and keep anything sown earlier and less hardy inside. I reckon this looks roughly like:

    Hardy and/or sown early (Feb/Mar):
    - Courgette - yellow
    - Courgette - Black Beauty
    - Dwarf French Beans

    Non-hardy and/or sown later (Apr):
    - Tumbler tomatoes
    - Tomato - Moneymaker
    - Sweet Basil
    - Russian Tarragon
    - Coriander
    - Chilli Pepper Padron

    For the herbs and Chillies, I will probably slightly stagger their sowing as you say, so this would mean I can put them in the cold frame from June anyway.

    All of the above apart from courgettes and basil are new to me, so fingers crossed!
  • FairygirlFairygirl west central ScotlandPosts: 35,520
    With basil - it's a good idea to sow  in a small pot [3 inch or so] and rather than pricking out when they're at a suitable size, just divide the clump into two or three, and pot those clumps. One sowing would give you three decent pots after a short while. Then sow again a month or so later, or sooner, depending on how much you use it. 
    It's a much more successful way of doing it than pricking out individual seedlings. We often get asked about it on the forum.  :)
    I only grow tomatoes and hardier stuff - lettuce etc, so I can't offer much advice on  your other veg, but there are loads of folk here who do, so don't worry. You'll get plenty of help with timings etc for the other veg. 
    It's a place where beautiful isn't enough of a word....


  • WildFlower85WildFlower85 Cambridgeshire, UKPosts: 166
    Great advice on the basil! I have it with everything. This year I tried to keep the same 7 plants going all summer by picking leaves and encouraging side shoots, but although it worked, the plants never got particularly bushy. Will try this more use and re-sow approach!
  • FairygirlFairygirl west central ScotlandPosts: 35,520
    Yes - a single pot won't last long enough, so you need to sow every few weeks.
    Lettuce is the same - you can use most varieties as a cut and come again, and leave some to grow fully. If you sow every few weeks, the 'cut' ones will keep you going for a long while - again depending on how much you use, but you'll also have a few mature ones too   :)
    It's a place where beautiful isn't enough of a word....


  • SkandiSkandi Northern DenmarkPosts: 1,045
    I wouldn't sow the courgettes or the beans before April/May. neither will take any frost and they grow fast.
    Chilies need sowing early if you want a crop so Feb, but they cannot go outside until all frost is gone.
    Coriander is frost hardy so that could be sown and go out earlier. (it also is fine direct sown) early sowings bolt pretty fast so you will want to sow them every few weeks as well.

    My last frost date is June 1st so I sow Courgettes in the first week of May, they have two true leaves by the first of June and are getting rather big for pots. Beans are sown the second week of May and have one true leaf by June.

    A Greenhouse/coldframe will only give you 1-2C protection at night so don't put anything frost sensitive out before you know the temperature is going to stay above 5C or so.
  • WildFlower85WildFlower85 Cambridgeshire, UKPosts: 166
    Thanks @Skandi. I realise my post made it sound like I would start growing from February but in fact, I have a whole spreadsheet prepared that tells me which veg seeds should be sown when, and only Tarragon and Radishes can be sown that early, with the rest mostly following in March or April. I certainly won't start growing courgettes and basil until April/May. I sowed this year's on 29th April but we did have a warm spring! We'll see what spring 2021 brings weather wise... :) 
  • SkandiSkandi Northern DenmarkPosts: 1,045
    @WildFlower85 yes not this year but last year all my stuff made it out a couple of weeks early, this year summer didn't arrive until August.. sigh
  • I've grown Broad Bean seeds which are now approx 4 inches, Onion seeds which are 3 inches, and sweet peas which are 3 - 4 inches. They are currently in the Conservatory
    Should I now get them outside with some covering? Havent got a greenhouse unfortunately but have something like a cold frame
  • FairygirlFairygirl west central ScotlandPosts: 35,520
    The sweet peas should certainly be outside with just basic protection from the worst of weather. They'll just become soft and leggy otherwise. Mine are just under a couple of perspex tables which have gaps, or in the growhouse with the lid open.   :)

    Can't help re the others - sorry. 
    It's a place where beautiful isn't enough of a word....


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