Optimal temperature for herb cuttings

I’m having mixed success at the moment with my herb cuttings. I appreciate it’s Winter so I have less fresh growth to play with and temperatures aren’t exactly ideal. I’ve lost 80% of my first round of Rosemary and Santolina cuttings due to rot, and I suspect the problem was not enough drainage/too dense potting mixture. I’ve since loaded the next round of cuttings into a more sensible compost and perlite mix that is much less damp. I’ve also upgraded from plastic party cup covers to placing the pots in a propagator above a heated mat.

However, I’m reading conflicting info online with regards to optimal temperatures and whether heating from below is an absolute must or an absolute no no. The propagator is currently in an unheated garage (near-ish to a window) but on a heated mat. The vents are closed and I open them briefly once a day to mist the inside. The thermometer inside the propagator is showing around 14C, which strikes me as rather cool, but then as I say some sources suggest too much warmth will aid rot/mould. 

Are these conditions too cool or too enclosed, or about right do we think? Again for reference I’m mostly propagating Rosemary, Santolina and a little thyme and oregano. Rooting gel has been used, hence I’m hoping for a little more success.

Posts

  • herbaceousherbaceous E. BerksPosts: 1,142
    Hello @djtheblade sorry to hear about your frustrations with your cuttings. You definitely need warmth to get any of the perennial mediterranean herbs to strike so the rosemary, santolina and thyme will do better under cover with a bit of warmth. I don't grow oregano as I prefer marjoram and I would wait until the weather is a bit warmer before trying to propagate as it has a much softer stem.

    Damp air can be a problem and it generally takes me about a dozen cuttings to get a good plant so I mainly take my cuttings in late summer or in the spring before they flower. Don't know if this helps but good luck anyway.
  • Hello @djtheblade sorry to hear about your frustrations with your cuttings. You definitely need warmth to get any of the perennial mediterranean herbs to strike so the rosemary, santolina and thyme will do better under cover with a bit of warmth. I don't grow oregano as I prefer marjoram and I would wait until the weather is a bit warmer before trying to propagate as it has a much softer stem.

    Damp air can be a problem and it generally takes me about a dozen cuttings to get a good plant so I mainly take my cuttings in late summer or in the spring before they flower. Don't know if this helps but good luck anyway.
    Yes I’ve been ambitious doing them in Feb. I may bring them indoors to raise the temp a little in which case. Thanks.
  • On the whole, I find bottom heat is best for cuttings such as described.  Helps the roots to form more quickly than the top growth which is what you want to begin with.
    Either a propagator with a heated base or a heat mat with a propagator lid should work.  Good air circulation is important as is the make up of soil/compost you use.
  • Have you thought about your compost too?  I use a 50/50 mixture of multipurpose and grit or sand.  These are mediterranean plants and used to growing in free draining dry soil.  I usually take my cuttings in late spring using good strong shoots before they flower and I keep them under the bench in my unheated greenhouse.  Perhaps I've just been lucky.
  • Thanks for the pointers. I’ve got a mix of compost and perlite at the moment and still seem to be getting quite a lot of mould development. If I remove the propagator lid for better circulation I’m worried none of the heat will be retained. Perhaps I need to let the potting mixture dry out more. 
  • TopbirdTopbird Posts: 5,299
    edited 19 February
    @djtheblade - I think these cuttings in compost would need to be kept really quite dry - but I also suspect trying to do them in February is not giving the best chance of success.

    There is quite a long running thread about rooting plants in water and I have certainly seen woody sprigs of thyme stuck in a glass on the kitchen window sill start producing roots within a few days. 
    Other people have had success with rosemary and plants such as artemisia so santolina might be a good candidate.

    The advantage at this time of year is that (IME) this method works better with firmer, woody bits of plant. It’s also very, very simple - literally shove the cuttings in a glass or bottle of water and wait for the magic to happen. Once you have some reasonable roots pot up the individual plants in small pots filled with very gritty compost.

    Link to the thread:
    https://forum.gardenersworld.com/discussion/1004868/plants-that-root-in-water/p1


    Heaven is ... sitting in the garden with a G&T and a cat while watching the sun go down
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