Growing seed for harvest 3: Leeks, celery and cucurbits

Organic NZ Magazine: Growing seed for harvest 3: Leeks, celery and cucurbits
Section: Farming and Horticulture
Author: Annie Wilson and Colin Walker

In the third of our series, Colin Walker of the Koanga Institute talks to Annie Wilson about saving heritage seed.

The Koanga Institute was established to develop a national network of growers to support the seed bank started by Kay Baxter and the team at Koanga Gardens and ensure the survival of traditional food varieties. By growing heritage seeds you can help.

Now that the main summer vegetable crops are all in the ground and growing well, it is time to think ahead to crops like celery and leeks that have to stay in the ground a long time before you can harvest their seed.

Celery (Apium graveolens) is a biennial and is pollinated by insects. Seedlings that are put in the ground in November will grow through the summer and winter and go to seed the following summer. It is therefore important to choose a good site in the garden where the plants can remain for this period of time.

Celery produces typical umbelliferous flowers and then equally beautiful seed heads. It is important to catch the dry seed while it remains on the plant, or it will drop and be lost. Shake it out of the seed head into a container and store it in a cool dry place.

When grown organically, celery ideally needs a dry climate because of its susceptibility to septoria (a disease otherwise known as rust) appearing as brown spots on the leaves of the plant. This is an issue that needs awareness amongst growers of seed because rust is a seed borne disease, meaning that the disease is transferred in the seed, so you risk the possibility of not only growing a new crop with rust present, but spreading it to other soils through that seed.

Leeks (Allium ampeloprasum) are biennial and are pollinated by bees. They take an equally long time to grow for seed, producing seeds in the second year. Seedlings should go into the ground in November in order to be harvested in the autumn of the next year. In very cold climates, plants remaining in the soil over the winter may need additional mulching with hay or leaves to protect them.

Early in the spring following, dig up the leek plants – including roots – that you have selected and therefore not eaten, and replant in a corner of the garden where they can stay undisturbed and out of the way. Thirty plants should be sufficient in the short term, but to maintain genetic diversity saving 60–100 plants is desirable. By the autumn, each leek will have sent up a single stalk over a metre tall, capped with a huge ball-shaped flower containing hundreds of black seeds.

These seed heads need to be dried well, and rubbed briskly to release the seed, then stored in the usual manner.

It is important to know that elephant garlic also belongs to the leek family, and so will cross pollinate with your leeks if flowering at the same time.



There is often confusion about the cucurbit family because of the different species involved. The main species grown in New Zealand are Cucurbit pepo, moschata and maxima. The varieties within each species will cross-pollinate one another, so choose just one genus from each species to save for seed in any given year. Don’t worry about crosses between cucumbers, squashes or melons.

Cucurbita pepo – this includes courgettes, vegetable marrow, scallopini, the Austrian hull-less pumpkin, yellowneck, acorn, gem and spaghetti squash. Kamo-kamo is probably also in this species. For pepo species, the seed continues to ripen after harvest so leave it in the fruit or let them mature on the vine for another month if conditions are suitable.

Cucurbita moschata – this includes butternut squash and Chuck’s winter, a large form of butternut which is a very good keeper with great, sweet flavour. Koanga also has the cupola pumpkin, an unusual, long shaped, seedless variety.

Cucurbita maxima – this includes buttercup squash, triamble pumpkin, the small green chestnut pumpkin, and all the common grey pumpkins. Koanga also has the red kuri pumpkin in their collection.

The seeds of the Austrian hull-less pumpkin, which are for eating or adding to bread, are very soft and so cannot withstand the wet fermentation process and should be cleaned only briefly of their pulp, in water and then dried.


Cucumbers and melons

Two types of cucumber (cucumis sativa) will cross-pollinate so again, grow only one for seed. Likewise water melons (citrullis vulgaris) will cross with each other, but not with rock melons (cucumis melo).

Select fruit for saving from a minimum of six plants. For long-term genetic strength you’ll need fruit from twenty plants. Mark or label them clearly so they don’t get harvested by someone else by mistake. Don’t keep seed from the first fruit, and ideally not until mid-season. As a general rule: when fruit is ripe enough to eat, the seed is ready for saving (although not courgettes and scallopini – which must mature far longer for seed) but ideally let the fruit go past ripe almost to the point of turning yellow before harvesting for seed.

For cucumber and melon, employ the method for wet seed, i.e. collect the seed with a little pulp and cover with water and leave in a sealed container for 3–6 days so that it ferments. Rinse the seed off through a sieve and clean the pulp from it, then dry the seed on a tray in the sun for at least a week. It must be very dry.

Pumpkins and squashes are also best treated with the fermentation process, but can be scooped of their seeds, which then get washed of pulp and set out to dry on trays or paper.

Give them at least a week of drying, then store in a sealed jar when you’re certain there is no moisture left. Next issue we will discuss carrots and early brassicas, and other crops sown in the autumn.


National seed survey completed

The Organic Seed New Zealand project has finally reached a conclusion and results of the work done can be viewed

The project was funded by the Sustainable Farming Fund and involved research into organic seed production and plant breeding in New Zealand. Twenty five crops were grown in 120 trials over three years. Results include information on seed borne diseases, production issues, availability of seed, and the skills required to grow for seed successfully.

It also researched international production, and a strategy for developing organic seed production in New Zealand has been developed.