treeblog Set D: pretreatment of the rowan seed

So I’ve (1) collected and (2) pre-pretreated treeblog’s Set D rowan seeds. Now they are undergoing (3) pretreatment before I (4) plant them in the spring. The last time I planted rowan seeds – for treeblog Set C – I neglected to pretreat them and my folly was rewarded by a total absence of germination. (So far… A year of ‘natural pretreatment’ and they may yet germinate alongside the Set D seeds!) This time I am boosting my chances of success by trying out three different methods of pretreatment advised by the Forestry Commission in their Practice Guide Growing trees and shrubs from seed by Peter Gosling (2007) [available online in .pdf format here].

Rowan seeds are classed as orthodox, deeply dormant seeds – ‘orthodox’ meaning easily stored and ‘deeply dormant’ meaning they ‘remain outwardly inactive under all conditions’, i.e. they require pretreatment to bring about germination. In the wild, rowan seeds would remain dormant for a year or two before germinating – the ‘natural pretreatment’ I mentioned above.

You’ll remember that I collected seed from two different individual rowans: a tree on Whitwell Moor and a tree above Oaken Clough. I kept each seed collection separate to find out if there is any difference in growth or form between the seedlings of the two trees. I also divided each collection into thirds so that the seeds of both trees will undergo all three of the pretreatment methods recommended by Growing trees and shrubs from seed. I’ve provided an abridged version of each of those methods below:

A. “Easy: natural (outdoor) pretreatment / sowing with medium”

1. Prepare a moisture retaining medium by mixing one part organic material (such as peat or decomposed leaf litter) with one part coarse particle material (such as sand or grit).

2. Mix one part seeds with one part moist medium and place in a container which is open to rainwater at the top and has drainage holes at the base.

3. Pretreatment: place container outdoors for thirty (16 – 30) weeks, positioned so as to receive exposure to seasonal temperature changes whilst avoiding daily temperature fluctuations.

4. Inspect seeds regularly (weekly to fortnightly) and if necessary re-moisten the stratification mix or remove decaying seeds to prevent the spread of fungal infections.

5. Remove and sow germinating seeds (or sow all seeds when 10% have begun to germinate).

A. On Saturday I filled two small plant pots with a one part compost, one part sand mix. Into one pot I mixed a third of the Whitwell Moor seeds; into the other I mixed a third of the Oaken Clough seeds. I’ve placed the two pots outside where they are open to rainwater but should avoid large fluctuations in daily temperature. There they shall remain until spring. Sixteen to thirty weeks from the 10th of October gives us a planting window open from the 30th of January to the 8th of May. I’ll probably plant all of the Set D rowan seeds proper in March.

B. “Moderate: artificial (temperature controlled) pretreatment with medium”

1. Prepare a moisture retaining medium by mixing one part organic material (such as peat or decomposed leaf litter) with one part coarse particle material (such as sand or grit).

2. Mix one part seeds with one part moist medium and place in a container, leaving a gap in the top.

3. Pretreatment: two (2 - 4) weeks warm followed by thirty (16 - 30) weeks cold. Use the main compartment of a refrigerator for the cold phase.

4. Inspect seeds regularly (weekly to fortnightly) and if necessary re-moisten the stratification mix or remove decaying seeds to prevent the spread of fungal infections.

5. Remove and sow germinating seeds (or sow all seeds when 10% have begun to germinate).

B. On Saturday I filled two empty yoghurt pots with a one part compost, one part sand mix. Into one pot I mixed a third of the Whitwell Moor seeds; into the other I mixed a third of the Oaken Clough seeds. I’ve placed the two open-topped pots in the fridge where I’ll ensure that they remain moist until spring.

C. “Skilled: artificial (temperature controlled) pretreatment without medium”

1. Place seeds in a loosely-tied woven bag and rinse / soak in cold (+4°C) water for forty-eight hours to remove any chemical inhibitors.

2. Drain seeds in a sieve to obtain imbibed, surface dry seeds.

3. Transfer seeds to a polythene bag. Leaving an air gap above the seeds, loosely tie the neck of the bag with a finger-sized hole to permit gaseous exchange but retard drying.

4. Pretreatment: two (2 - 4) weeks warm followed by thirty (16 - 30) weeks cold. Use the main compartment of a refrigerator for the cold phase.

5. Inspect seeds regularly (weekly to fortnightly) and if necessary re-moisten the stratification mix or remove decaying seeds to prevent the spread of fungal infections.

6. Remove and sow germinating seeds (or sow all seeds when 10% have begun to germinate).

C. On Saturday the 3rd of October I started separate 48-hour soakings of the Whitwell Moor and Oaken Clough seeds. I rinsed the seeds two or three times during the 48-hours. A week later (last Saturday), I transferred the surface-dry seeds to two small polythene bags and placed them in the fridge.

* * * * *

So there you go. Will the seeds make it through the winter? Will any of them germinate next spring? Will there be any difference between the Whitwell Moor and Oaken Clough seedlings? Which method of pretreatment will be the most successful? Only time will tell!!!


Posted in Dendrology + The treeblog trees










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