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Swan Plant Tips:
Jacqui Knight

31 March 2023

We receive many requests throughout the year about raising healthier swan plants. I have been picking the brains of some of our horticulturists – although not many profess to be experts on boring old swan plants! If swan plants were roses or popular food crops, no doubt there would have been in depth analysis of the diseases that affect them. But they’re not. So while we monarch lovers can’t identify many of the issues affecting the plants we can at least do what is within our power to raise healthier plants.

If you are starting out encouraging monarch butterflies you will find that most of the plants available in the spring in garden centres are “seedlings”, about 15-30cm tall. There is nothing wrong with that – but do not think these are fully grown swan plants. The seedlings have been started by commercial nurseries over the winter and into the spring and kept protected from aphids and monarch butterflies so they are in great condition when they go on sale. Quite probably insecticides or fungicides have been used in their production.

A large, fully-grown swan plant could be 2 metres tall or even more and having them established before the monarchs return from overwintering is a huge boon. So as you buy or grow your plants, think about them for next year and subsequent years.

In many parts of the country, it is possible to raise swan plants which will last for two or three years. In cooler areas you could try them on the sunny side of the house, under the eaves, but you might need to offer protection from frosts or snow of course. And you could try getting Asclepias incarnata established. This is very successful in colder areas as the shoots appear soon after winter weather retreats, and grow much quicker than any swan plant seedling. It establishes with an underground root system and the patch will get bigger each year.

Here in Auckland, and towards the end of the season I take stock of my swan plants and remove any that do not look healthy: actually, I do this throughout the season, putting branches inside the butterfly house so that the leaves are eaten before I dispose of the bare branches. I do not compost them if I think they may have a plant disease. (A plant disease will not affect the caterpillars but could spread to other plants of course).

I am not well disciplined enough to sow from seed but depend on a very good friend to provide me with seedlings. However, check out the method Gus Evans uses in his guest editorial in the blog. There is no right or wrong way.

And here is a very useful leaflet from Yates about growing swan plants from seed.

Once I have seedlings, I ensure they get a good feed of Nitrogen once a week and I only repot them when there are roots coming out the bottom of the pot. Remember, swan plants are weeds or wildflowers and have not been fussed over or improved by plant breeders over the years, so you should not fuss over them either. There are different ways you can give them Nitrogen. Nitrogen encourages healthy leaf growth.

You could try Tui® Nitrophoska-K or Yates® Thrive Natural Fish and Seaweed, a concentrated plant food. Or sheep pellets, blood meal, diluted human urine (10:1), compost tea, seaweed tea, worm wee. Worm wee makes soil far richer than it could ever be on its own. I have heard that worm castings have five times more nitrogen than regular soil! Unlike chemical fertilisers worm tea will never burn plant roots, no matter how much is applied. If you have access to comfrey or Tithonia diversifolia, these leaves are also rich in nitrogen.

As your swan plants grow it is absolutely natural that the older leaves go yellow and drop off. You will also notice that the stem gets thicker and taller… and there are new leaves at the top. It is fascinating watching the plants grow. When they are about 20cm or so, you might want to pinch out the top of the plant. This will mean that two lateral stems will start growing out at angles, so your plant has just become twice as productive. After those laterals are 10-15cm, you might want to repeat the exercise. Now your plant will provide four times as much food for caterpillars. There is a video on our YouTube channel with some more tips for swan plants as well.

If you see curled leaves or leaves with black spot you can remove them. Do not compost these as you run the risk of spreading fungus or bacteria spores to other plants or into the soil. Diseases can be spread by ants, aphids and passionvine leafhoppers, so control these pests. In ongoing humid weather the problems become exacerbated.

Spots on stems and leaves can be a symptom of a fungal disease. Get in early to start controlling it on young plants. A copper fungicide will kill bacteria on contact. Yates® Liquid Copper is an easy to use, broad-spectrum copper fungicide and bactericide. Check that other copper products are not mixed with an insecticide.

Spray the plants before the monarchs return from overwintering and your plants should stay healthy throughout the season.

You might have heard of the monarch disease referred to as Oe (short for Ophryocystis elektroscirrha) which is carried by female monarch butterflies. As she lays eggs, if she is infected, she will also leave behind spores of Oe on the egg shell. When the caterpillar eats his way out of the egg it will be infected.

The disease can become most apparent when monarchs are raised in cluttered or unhygienic conditions as the disease has a chance to spread. The result will be sick and dying caterpillars, butterflies that struggle to eclose or malformed butterflies.

If you suspect your plant is carrying Oe, left behind by monarchs on the leaves, or other plant diseases, you can spray them with a bleach solution of 1 part of bleach to 19 parts of water. Ensure you buy regular bleach (not with other ingredients such as lemon) and wash the bleach solution off the plant with fresh water after ten minutes.

If you have plants in pots you will need to water them. But in the garden, always water at the base of the plants and invest in sustainable practices to ensure you minimise the need for water. This is not only good for your garden but good for the environment too. I recently watched an excellent series on the soil food web, restoring nature to the soil and highly recommend it so you can understand sustainability in your garden..

Yellowing leaves further up the plant, or stunted growth can be a sign of nitrogen deficiency so keep up the regime of feeding your plants. Do not expect all of your plants to thrive, but if you follow the above ideas you should have more successful swan plants. And feel free to add comments below with your own ideas. As I said, there is no right or wrong way. What will work for me may not work for you. But it is great to learn what others do.

Also, have you checked out the video on YouTube with tips for getting more out of your swan plants?

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