Plant swan plant seeds early

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This time of year is a great time to sow swan plant or milkweed seeds. There is still enough heat to encourage germination and your plants will have a chance to reach a reasonable size before the cold weather slows them down. March and April still have plenty of good warm days and the soil still has enough warmth to nurture a seedling.

We have all had the experience of running out of fodder for our caterpillars and frankly it doesn’t matter how many plants you grow, there will never be enough because the population dynamic will ensure that even if you grow a plethora of plants, as a result you will attract a multitude of butterflies and many more eggs will become hungry caterpillars.

The lesson to learn here is to start early and get a head start on planning for next spring. Buy good fresh seed from a reputable supplier such as the MBNZT. These will arrive pronto especially if you purchase them online. 

Always use a good potting mix or well matured compost with a reasonably fine texture. A warning to anyone using dusty, dry lifeless soil – like any small living thing, if you starve it, you will have unsatisfying, mean results so always use good soil to give your seedlings the best possible start.

Water is essential for good plant growth and your soil or mix should be damp and not allowed to dry out, while not sitting in pools of water where root rots will see your plants withering. It is quite hard to strike a good balance with water especially if you have sown your seeds in seed trays and their root run is limited by the depth of the tray. Pay attention and check your seedlings every day. If the weather is hot, cast your eye across seed trays twice a day. Keeping trays in a semi-shaded spot with morning sun only will help them retain moisture and still have enough sunlight in the mornings to drive a good growth rate.

Be ready to transplant your seedlings into small pots. Have good soil or mix on hand and when seedlings reach a point of having four good leaves, carefully pot them on into small pots which will allow a bit of growing on room. Pots around 7cm across will be sufficient. If you use pots that are too large and the roots cannot reach the edges before the winter sets in, your seedlings will become waterlogged and cold during the coldest months.

Keep the small pots huddled together over the colder months where they will afford each other some protection from the coldest winds and wintry onslaughts. Use a porch or a spot under a tree or next to a hedge to offer a bit of shelter during the worst cold snaps.

Plant what you consider to be far too many seeds! It’s great to have plenty, and plants make lovely gifts for anyone interested in caterpillars and butterflies.


Written by Jane Carver for Moths and Butterflies of New Zealand Trust. For more information about Butterflies or to become a MBNZT member pleases visit



Swan Plant & Monarch Butterfl
Swan Plant & Monarch Butterfl