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Advice on growing on from plug plants (herbaceous perennials)

DevonianDevonian Posts: 176
I've recently been buying plug plants as a cost-effective way to create the numbers I need for garden borders. These are pretty much all herbaceous perennials plus some ornamental grasses, although I try to buy them as 9cm pots as they're slower-growing.

I'd really like advice on how best to grow these on - so far I've been potting straight on into 9cm pots with MP compost, kept moist and fairly sheltered (actually inside a very light-filled shed with doors open for ventilation).

If any of you experts has advice for a novice on how to get the best growth out of such plants I'd be very grateful!

If it helps, here are some of the plants I currently have growing from plugs:

Penstemon (various types)
Hosta (Wide Brim)
Alchemilla Mollis


  • FairygirlFairygirl Posts: 52,199
    I wouldn't keep any of those undercover of any kind - even when small.
    Completely hardy.   :)
    It's a place where beautiful isn't enough of a word....

    I live in west central Scotland - not where that photo is...
  • Butterfly66Butterfly66 Posts: 886
    They can all be outside. Unless they’ve got lots of competition in the garden I would probably plant them all straight out. Easier to look after and no more vulnerable than in pots.
     If you have a garden and a library, you have everything you need.”—Marcus Tullius Cicero
    East facing, top of a hill clay-loam, cultivated for centuries (7 years by me). Birmingham
  • AnniDAnniD Posts: 11,441
    If you wanted to grow them on before planting out, as others have said they will be quite happy being outdoors. They're the tough ones  :)
  • DevonianDevonian Posts: 176
    OK great, thanks! The main reason I'm growing them inside is because for some of them I don't have the beds ready yet, and I didn't want the pots to overheat outside! I'll find a spot for them with at least part-shade until I can plant them out.

    Thanks all
  • B3B3 Posts: 25,260
    Overheat? You must have some microclimate there😉
    In London. Keen but lazy.
  • DevonianDevonian Posts: 176
    B3 said:
    Overheat? You must have some microclimate there😉
    LOL, sadly not - my fault for placing the pots in the full sun! I'll find a nice bright shady spot for them from now. Thanks!
  • PosyPosy Posts: 3,601
    I'm inclined to disagree! In my experience, plug plants are usually only a couple of inches high with short roots. They need protection from drought, strong wind and pests. I would keep them in a sheltered corner, in dappled shade, until they have filled the 9cm pots, and even then, unless I had ideal conditions, I would pot them up again.
     And as for heat, on Sunday and Monday, we had virtually the first rain since March. We have had wall to wall sunshine, quite high temperatures and some strong breezes. Not good for baby plants.
  • Agree with @Posy and I have found due to the failure rate of plug plants that it's not a very economical way to grow...too many perish in transit or get too stressed. 9cm potted plants are cheap enough and will grow to double the size in one season.
    To Plant a Garden is to Believe in Tomorrow
  • DevonianDevonian Posts: 176
    Thanks @Posy, yes I'm going to keep them in a sheltered shady spot til they're at least filling 9cm pots (some of them potted up a month or so ago seem to be almost ready to pot on).

    @amancalledgeorge I've actually had really good success so far. Out of around 40-50 plugs, only 1 has failed and the rest grow beautifully! I was finding less success with 9cm pots at the moment as so many seemed to arrive very pot-bound and obviously not been given the usual care and attention whilst nurseries deal with the Covid-rush!
  • GreenbirdGreenbird Posts: 237
    I planted 21, 9cm foxgloves plugs straight into a semi semi shade bed. 

    I planted 10, 9cm Lavender plugs straight into a sunny bed.

    I ordered the 40 lavender plugs from Gardeners World a few issues ago which I'm growing on in larger pots in a sheltered corner.

    No losses so far.
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