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Wednesday, May 29, 2024
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You can get some stratification

The seasons have properly turned with a slight scattering of snow on the Tararua Range and a couple of killing frosts.

The chilly nights have meant the demise of the last of the dahlias, so they have been cut down.

The tomatoes had largely been removed from the garden because they had mostly run their course, but Honeybee [a supposed dwarf variety that has grown well over two metres] is growing very strongly still and continuing to produce masses of small yellow globe-shaped fruit. It has been fruiting so prolifically that I have been made some tomato sauce entirely from its fruit.

This plant is growing underneath the eaves on an east-facing wall and is still happily flourishing despite having the outside leaves darkened by the frost. Time will tell how long it will last.

Funnily enough, I have been looking at the effects of cold on the opposite end of the growing cycle.

Each Christmas, I watch my Christmas lilies grow, and I think – “I wonder if they will cross with other lilies”, so last year, I crossed them with one of my favourites, ‘Lady Alice’. This is a hybrid derived from Lilium henryii and has reflexed petals that are apricot-coloured with white edges.

The seed pods filled up beautifully and I kept a close watch on them as they matured, because I did not want to the pods to split before I harvested the light seeds within.

While I waited, I looked up some literature on crosses with the Christmas lily, L. regale, and found some breeders saying they thought they had achieved hybrids with it, but in each case the plants all bloomed as pure L. regale.

At first, I was disappointed then I thought that if I raised these plants from seed and ended up with a big batch of Christmas lilies – well, there could be worse things than that!

The germination of these seeds will be a little tricky. Many plant species have evolved germination blockers to prevent them from sprouting at the wrong time of the year. However, these impediments can be overcome with a little thought.

Most perennial plants come from areas with very cold winters and have evolved techniques to stop their seeds from germinating in the autumn when the seeds first fall or in the middle of winter, when they would be killed off by frost.

They require a period of cold weather followed by the warmer temperatures that signal the arrival of spring and better growing conditions.

To overcome these roadblocks to germination, nursery owners and plant breeders use a technique called stratification. The seeds are placed in layers in moist sand and stored in sealed containers until the blockers have been surpassed.

There are two different kinds of stratification – warm and cold. For many plants, the seeds drop in autumn and have a mild period before experiencing winter, so to duplicate that, a warm stratification can take place, where the containers are kept at room temperature for a month or six weeks. Following that they are placed in the bottom of the fridge for a few months, before sowing in the spring.

Christmas lily seeds require such a process so I will have to check with the Head Gardener that she does not mind a container or two of seeds sitting in the bottom of the fridge, rubbing shoulders with the bottles of milk.

Of course, many plants have had this process bred out of them. Almost all our popular vegetables probably had germination inhibitors in the DNA, but many generations of choosing only those plants that successfully germinate easily has meant that element has been bred out of them. Ease of germination is something that is a determinant of how successful a new vegetable strain will be.

Some cucumbers require the right temperature to germinate. In the nursery we used to place some of the more expensive hybrid Telegraph types in moist materials atop a hot bed and always keep them moist until they germinated. They had to then be pricked out very quickly as the roots would penetrate the material making them difficult to move. That was critical because it was expensive – over $1 per seed.

Some perennials exhibit an extreme form of stratification. If kept in warm stratification a root will develop, but no leaves – these are only initiated by a period of cold stratification. In the wild these plants usually produce the root in the second summer after falling, then the shoots the following summer.

In a little twist, some seeds seem to have inhibitors that need to be washed away. In that case, some breeders place the seed in a mess bag in the cistern of the toilet, ensuring that the seed regularly has water flowing past it, washing away the inhibitor.

I have used the technique for Pacific Coast irises and it works well. And no, the flowers were not flushed with colour!

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