Galium aparine is a species widespread in the temperate and Mediterranean areas of the Northern Hemisphere. It occurs naturally in hedgerows and is a major weed of winter and spring cereals, rape and even of summer sown crops in some areas. There are distinct genetic differences between populations. Differences in the germination requirements of separate seed batches is a problem particularly in glasshouse experiments.

Galium aparine is often a problem to germinate in summer. It is believed to have an endogenous time clock which limits germination to autumn, winter and early spring. Also, it often has a requirement for low temperatures and abundant moisture. Low night temperatures may be particularly important. The same batch can vary with time from requiring darkness for germination soon after harvest to requiring light for germination of older seed. The species is notorious with glasshouse weed screeners for these reasons. There are ways around the problem but different methods seem to work for different people (and different Galium populations and at different times). The best approach is to try several batches of seed and several sets of conditions to see which works best for your seed batch and environmental conditions. Try the following:

1) Stir the seed into the top 2cm. of soil such that some is up to 2cm. deep and some on the surface. Place several trays or pots so prepared in a range of environments, with in particular emphasis on cool shady conditions. Top water copiously and frequently.

2) Prepare seed trays or pots as above, water, then place in a cold room at 0C-5C. Do not let the soil dry out. At weekly intervals remove one unit and place it to germinate in light, preferably with temperatures fluctuating between 10C and 20C.

3) Soak seed for 1 hour in a 3% solution of potassium nitrate. Drain but do not wash. Place in an open topped container in a refrigerator at 0C-4C for a week, then sow.

4) Soak seed overnight in running water at 60C, then sow and germinate at less than 18C

5) To overcome the time-clock problem, deep-freeze a batch of seed when it is germinating well in winter and use this frozen seed during summer.

6) In summer, use HERBISEED's continental population of Galium aparine which seems to continue germinating later into the summer than some English populations.

7) Galium is reputed to germinate better in soil than on artificial media such as filter paper. Aqueous extracts of soil are said to stimulate germination on artificial media.

8) For field trials sown in warm soil where the Galium may germinate more slowly than other weed seeds, the Galium can be pre-germinated as follows; Soak the seed overnight in an aqueous solution of 1%-3% potassium nitrate (experiment with concentrations if possible). Drain but do not wash. Then put in a cold room at 7C-10C for 1week at the end of which the seed should have begun to germinate. This pre-germinated seed can then be surface dried on cloth or filter paper and mixed with a small quantity of dry sawdust for sowing into field trials.

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