Over the past week many areas here in Australia have seen varying amounts of rain during our planting and early growth period. I have had a number of requests from new growers for advice including ‘I’ve been told not to water my dahlia until it is 15cm tall, do I need to dig up my tubers than haven’t spouted yet’ to outright panic that recently planted tubers have received some rainfall and ‘what do I do?’
Firstly…..don’t panic! As a grower it is completely understandable that you are worried about your tubers…..they can be expensive and some varieties very hard to source if you need to replace them.
The general rule of thumb is that tubers don’t require additional water until they are approximately 15cm tall and are establishing a nice healthy root system……..however, this is dependent upon a wide range of varying factors that you need to take into consideration including tuber health when planting, the quality of your soil/growing medium and how free-draining it is, whether you have planted in pots, raised beds or in the ground, your local climate and temperatures etc. The requirements will not only be different for every grower, but usually varies from season to season as well.
Tubers need a damp-moist environment in which to thrive (not wet-soggy). It is important to monitor your soil and then act accordingly. Dig down 10cm in your soil with your fingers (away from the tuber as to not disturb any roots or potentially snap off a newly emerging shoot……yes I’ve been there!!….but if you do snap one off don’t fret, you will very likely get not only one but multiple shoots in it’s place) and check that the soil has sufficient dampness. The top inch of your soil may appear wet / or dry….but can be very different a few extra inches down. If the soil is dry – give it a water.
I grow primarily in raised beds, as well as 40cm pots (because I can’t say no to new varieties each sales season and run out of space in my beds). The soil and growing medium has been well prepared over each winter and is well draining. In the event of a heavy rain, the beds and pots are all on a well-draining base of compacted road base and stone so the pots are never sitting in ground water. If your ground does hold the water under your pots simply raise them up a bit…..I avoid this in my area as any gaps are likely to hide brown snakes which is something I definitely don’t want! The benefit of growing in pots is that you can also drag them in under cover of a patio or carport if needed.
In my beds, when my soil is on the drier side I usually need 15-20mm of steady rain for the water to even reach the depth of the tuber, so any less rain than that and I am not concerned at all. Recently there have been forecasts of 20mm of rain several days in a row, which I am also not concerned about given I am confident about the drainage of my soil.
The only time I would be concerned is if I was planting in heavy, poor draining soil or in the ground and the ground was flooding and not draining the excess water away. Last planting season was wet, we had many days of 50-80mm of rain in the first month after tuber planting, on these days the pots were dragged under cover, then the raised beds containing another 250 tubers were draped in long sheets of clear builders plastic, under which any tubers that were shooting above the soil had an upturned pot placed over the top before covering with the plastic so the shoots didn’t get damage. The sheets were then pegged down to avoid blowing away. This was a last resort due to the sheer volume of rain and as soon as the rain had cleared the sheets came off for airflow and to avoid cooking new shoots under the plastic. The reason I did this is that several of my beds had new soil which was heavier than I would have liked and wanted to hold onto the water for too long, which I gradually resolved over the growing season with gypsum and additional work over winter.
Whilst I usually dig up all of my tubers for overwintering so that I can plant green manure cover crops during winter and rejuvenate the soil, each year there are odd tubers I have missed that stay in the cold wet soil all winter (down to -5 degrees and heavy frosts, rain), those tubers are still happy and ready to grow when I discover them in early spring when I am digging in the cover crop, which reminds me how tough and resilient they can be.
Over the years I have learnt to let go of the stress and use any failures as a learning opportunity. Sharing of information and experiences is really helpful for new growers, but remember there are no hard and fast rules that work for every grower every season. Flexibility and adaptability is critical. Get to know your planting environment, over time learn how different weather and condition impact your growing, and hopefully each year gets easier and more successful.
In the coming weeks I will do a detailed post about growing dahlias in pots, in response to a range of questions coming through…..so stay tuned.
