When to prune swan plant?

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  • #13770


    Hi all

    As you know, I’m not good a growing things botanical. If a seed or plant grows in my garden, it’s Nature at work.

    We are getting lots of inquiries (emails to the MBNZT) asking about pruning milkweed (e.g. swan plant) and I ask people to please post their query in the forum… but they don’t. Neither do they tell me what part of NZ they’re in. Also what sort(s) or milkweed you’re working with.

    I would be grateful if you would post here what you do or intend to do, when (and where you are).

    Hope you will help!


Viewing 25 replies - 1 through 25 (of 25 total)
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  • #38322


    I’ve “pruned” mine many times. Chopped, more like. They get too big for the area, so I just take the clippers and chop off the tops. No problem, they grow back and thicker than ever (as someone already mentioned). I’ve done this in all four seasons except autumn (since this is the first autumn for these plants).

    I’ve never lost a plant to anything at all, but then we live in Thames, which has wonderful weather all year round. No frosts, not real bad heat, but lots of wasps. I water my swan plants, though. I’m not sure if this is standard practice for others, but our water is free, coming from a spring-fed creek, and I water just about everything on our 2/3 acre.

    I’ve never had any problems starting cuttings from swan plants, either. I was too ignorant to know it might not be possible. I just cut them, and not always “under 10cm in length.” Again, too uninformed to know better, I usually put about 10 cm below ground and the same above ground — always at least two nodes into the ground and two nodes above the ground. No rooting hormone, just stick them into a pot of homemade compost. And they’ve all done well.

    Transplanting is always a shock, and so I prune off about a third or so of the tops before putting them into their new location and then water really well right away.

    I’ve also grown some from our seeds, though I’ve never had 90% success rate on those. It seems easier to start from cuttings, but I do both. When I chop some off my growing swan plants, I will often stick them into a pot of compost and water them. And you can grow more than one in each pot. I’ve had as many as six in one pot, though it was a largish pot (maybe 10 inches or so).



    Pruning is going to be a biggy for me this year, our plants are very tall , many over 6 foot, but they are very spindly. I have had most success growing them in groves in rows about 3 deep and 10 or so across. I plant in different areas of the garden and spend many delightful hours removing the caterpillars that have reached a decent size to one grove or the other. I find keeping majority on one grove at a time will strip a lot of foliage but it will recover quickly when you switch groves. It lets the other grove recover.

    The tricky bit for me will be when to prune, I have a load of seed head for the first time this year and am plotting on growing as many plants as i can from them and encouraging neighbors have have developed an interest to also plant groves.I don’t want to prune until the seed heads are all matured , perhaps spring is looking like the ideal time.

    I might give cloning some cuttings a go and these are my obvious strong plants, many failed in setting up the groves. Survival of the fittest I guess.

    Oh and I am in Napier if anyone is wondering about growing conditions.



    I am in Dunedin and where we are by the sea we havent had any frosts yet; we dont get many anyway and I never loose plants to the cold, however wind is another matter and unless they are pruned, both those in pots and in the ground can keel over if left to get over head height.  That is if caterpillers havent stripped them.  Pruning also thickens out the plant.  Even if caterpillers have stripped the leaves they dont usually reduce the height sufficiently.  I prune either autum or spring,  depending on whether there are seed head to retain, or in the spring if there is unwanted growth.   The caterpiller stripped plants are sprouting again nicely at the moment so I dont do any more  pruning now to let the new growth come away.  And it is suffiently cold here for that new growth not to be very sappy and tender.  Some years though it is that growth that gets a bit hit by frosts

    I dont have to worry about frost cloth, some of the plants on the south side of the house get a little knocked back with the winter, but that is a combination of lack of sun, cold and southerly winds

    To give an idea of the climate, I still have aubergines producing outside at the moment and the last of the tomatoes willl not get picked until June.

    Because growth throughout the year  is slow though compared to the  north, the plants are hardier and sturdier come winter, which helps to make them cold hardy.

    I also rely on older plants for flowering, and caterpillars. The new seedlings will not make suffieient growth in one year to supply the monarchs.

    In addition to autumn  and spring pruning I also tip  prune the main stem (pinch out the tip) in the first year if it is a vigorous plant to ensure that the branching occurs at a low enough level, again this is to keep the plant at a reasonable height.   I like branching to start at about 500- 600mm.

    I hope this is of help to those in more southerly lattitudes



    Michelle that’s an amazing success rate. None of mine germinated. I am thinking of buying a heated pan and container (from Bunnings) to use late winter to try to get swan plants earlier in the season. The nurseries produce them too late. I’d love to meet you over a coffee somewhere. I’m in Seatoun, cell is 027 8426773. Please send a txt if you’d like to meet!


    I have a 90% hit rate on my seeds, I soak in water overnight, then plant into pots, then when big enough put in the garden. We are in Miramar Wellington, Sandy soil, does not seem to like growing wild seeds at all. We also get nasty frosts, like this morning. I just prune off branches when the frost’s finish. I try to keep plants for 3 years, no longer as they get to woody. I also plant in different areas so when one lot is eaten I can put the caterpillars onto the emergency food (south facing) that the butterflies ignore.



    I empathise with your situation. Plants cost a great deal of money. I think it is impossible to grow enough plants, because if you had thousands of them…..they would all be eaten to sticks.

    I have let my plants seed around the place, and unfortunately, they seem to always come up in annoying places and thrive there! I try to move a few to places where they suit ME. However the happiest ones are always in the middle of the vegetable garden where they are a perpetual nuisance! I have found it very useful to plant some on the shadier side of the property where they are slower to colonise with caterpillars and therefore do not get stripped so soon. Caterpillars can then be moved across the garden to complete their growth. This all turns to custard as the season ends, but by that stage there have been at least four generations.

    Seeds sometimes take ages, and often when I have given up on them and they are discarded into a corner in disgust…….presto,  seedlings then appear.

    It sounds to me like you are doing everything you can!



    Pepetuna and  Jane, thank you for your helpful replies. Last season I tried to germinate seeds (approx 50 of them inside early spring) and not one grew. The seed came from Waiheke Island. As for my potted ones most are under the eaves now. I really want them to survive the winter because I must have spent more than $350 this season buying swan plants!



    Hi Caryl,

    Your plants in the ground won’t need heavy pruning and certainly not to the ground. Cut off any stems that look less than healthy and leave the rest to take thier chances. It’s true that frost cloth could make a bif difference if you can be bothered. At the end of winter if these bigger plants don’t come away to your satisfaction, then take them out and throw them away. Always get some new plants each year as well, so there is a continuation. If  plants are in pots they appreciate being brought in under the eaves of the house.

    I lose several plants each winter to cold, frost, and any number of ailments. If you have room for many plants at various stages, then you will always have some that are doing well.

    I experimented this year. I left all my large plants to the elements without any interference, and have lost most of them to the oleander aphid. The parasites did take hold of many aphids, however the population dynamic was not in MY favour and the result is plants alive, but covered from top to bottom is aphids, aphid parasites and sooty mould. I will remove those plants to avoid them becoming a haven for disease. Lesson learnt!



    I’m in the Waikato where we do get frosts. Last year I overwintered hundreds of plants, covering them with frost cloth daily. It was a bother, and although they did come away eventually in the Springtime after minimal pruning, they didn’t grow as fast as the plants I grew from seed. So this year I am not going to bother with frost cloth and will grow all new plants.



    This is regarding ‘taking the seeds off the whispy part’

    I get the seeds with the fluff, pop them in a tupperware container with a couple of small coins, and shake it around. Eventually you will be left with a ball of fluff which has separated from the seeds.



    I’m in Wellington and have many swan plants in pots, many eaten to the stalk. Some though have plenty of leaves. I note that some enthusiasts use frost cloths to protect their plants. Where I am we don’t really have frosts but it gets very cool. Last winter I didn’t get many plants surviving the winter. Should I prune the ones with leaves heavily? I read that I should prune them to ground level, place mulch on top and feed throughout the winter. I cut back many of mine last year, didn’t mulch and only a few survived the winter. Essentially the season is over for monarchs here, although I have a few caterpillars and chrysalis left but doubt they will survive. How far should I prune back the few plants that are in the garden rather than in pots? Any tips I would be so grateful for.




    Taking cuttings is something I could go on and on about and bore you all to tears, so I’ll stick to the basics and if there are questions please sing out:-

    It is a good idea to take cuttings of your favourite plants to make more. Bits and pieces from your garden are like gold to your friends and family. The big advantage of cuttings is that you will get an exact replica of your parent plant (unlike seed where you will get crosses and hybrids)

    Cuttings should always be between under 10cm in length, cut the stem just below a leaf node (where a leaf has joined the stem), use a root forming hormone.

    You can purchase root forming gel from your garden centre. If you have Willow or Weeping willow nearby, you can make your own by simply soaking willow leaves and stems in water for a day then drain off the leaves and stems and the liquid left over is root forming hormone. Make fresh each time.

    Leave the base of your cuttings soaking in your root forming hormone mix for a few minutes or even overnight if they are not in too hot a place.

    Place your cuttings into a pot filled with a gritty mix.

    Keep damp. Place in a nice warm place in good light (a windowsill will usually do the trick) watch that they never dry out, and depending on the type of plant, you should have roots formed on your cuttings in about 4 – 6 weeks.

    This link gives a reasonable guide on how to go about it.




    Hi Blutterfy

    For the uninitiated, please share how you would treat “any other cutting”. Some people in here are not good at getting plants to grow (e.g. yours truly).




    I usually trim my plants back a bit to achieve a desirable shape. This year when I cut off some pieces about 10cm long I thought I’d see if they would strike as cuttings..AND THEY HAVE!! It has been a good start for some more plants. They took root so easily that I wondered why I hadn’t thought of it before. Treat as any other cutting : )



    I’ve never had to do it, since I find the Caterpillars are good at it.

    But if I was, then I think Spring could be good to avoid shock from frost. However, I could see a arguement for Auturm as the sap maybe getting pulled back to the roots (as in many shrubs), so then there’s less ‘bleeding’.




    A friend told me she had heard it was good to prune! (We are North Island, Devonport on the North Shore of Auckland) but having read the above, I think I will leave it alone! I have two large bushes each with about 20 seed pods on each plant. I will post you some of the seeds. Does anyone have a good way of taking the seeds off the whispy part?



    My mum just cuts bits off that are in the way or touching the ground. With the big frost that have been this year I don’t think any pruning should be done untill the Sept/Oct frosts have been. I have lost a few of my seedling and last years plants to the cold winds and frost this year.


    rachael mabbott

    Hi! This is great! We are new memebers. Not new to the monarch cycle though!! I grew up with my mother doing it, now i have kids, we are doing it! Just last year got really interested in it. We have 100’s of plants, variying stages. let go hundreds of butterflies last season. I’m wanting to know the best time to ‘top’ them, to then carry on another succesful year! in the past i have just let nature run its course, and trimmed them once they have rejuvinated in the spring. Scared if i do it now, the frosts may still kill them? Does any one have ant tips, knowledge on this? We live in Te Awamutu, south of Hamilton.



    We live in West Auckland (Massey). Our swan plants grew really well in the ground. Around June Allan cut the plants back by half. Most of these plants were around 5 to 6 foot tall and Allan has chopped them back over half way.

    The plants are doing really well and new growth coming through already.
    Jacqui will take some pics soon and send to you. Before and after pics if you like. Then everyone can see exactly what we have done.

    I intend to start using my Ocean Organics Foliar spray soon to get the leaves nice and luscious for the new season.

    Hope this helps.




    I won’t have any survive this winter, but in the past I have snipped off what’s left above the uppermost shoot in the Spring. What’s left above is usually dead anyway.Even if the shoots are at the base and nothing above, I snip it at the base above the shoots.(About 10mm above the shoot or you’ll have die-back). Bryan. Cambridge, Waikato



    yes i have, i did it once,i decided to cut them back by a third – at the end of summer, they ‘bled’ alot of milk and i think i nearly killed them! Now i trim the odd branch (if its going to stick out from under frost cloth) but i will never prune again. (timaru)



    I have never grown swan plants successfully J. They grow in gravel, scoria but never where I want…. never had a chance to prune them cos they get eaten…. oh yes, I live in Bay of Islands…. 🙂 🙂 Sorry Mrs J….:D



    In previous years, did you prune them?

    If so, can you share a few tips for ohers – and tell us where you live please. I know you live in the Bay of Islands, but others may not.



    Ummm… I don’t have any swan plants left! They have all been pruned by a certain bird 🙁
    Or pulled out by the roots!



    Hi Jacqui
    Pruning milkweed??!! If only they grew that well here in Wakefield, Nelson. I have 2 pots of tiny plants in the glasshouse under frost cloth and they don’t look at all happy, but once these hard frosts are finished it will be out with the plant food and stand back ……
    Regards, Jean

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