The importance of mulch
Mulching your dahlias will prevent weed growth, keeps the roots cool and also eventually helps soil structure
Many dahlia growers grow their plants through a mulch material. This can be a weed membrane or organic material such as straw or compost. I prefer to use barley straw at a rate of one bale per 20 plants. This gives a layer of around 15-20cm (6-8in), which over time will compact down to around 10cm (4in). This can be applied at any point of the growing season, but it's easier to get it around the plants when they're smaller. The disadvantage, in my opinion, of using weed membrane is that it's usually coloured black and, as we know from our own clothing, this can attract the heat.
What are the advantages of straw mulching?
There are several advantages of using barley straw as a mulch and these include: Preventing weed growth
Keeping plant roots cool
Reducing frequency of watering and feeding Preventing the soil from cooling too quickly, giving a more even temperature, meaning the flower opens consistently over the 25 plus days of development
It can be dug into the soil at the end of the year and will help the soil structure.
Just make sure that any straw you use comes from a reliable source and is free from any residual herbicides that can later leach out and stunt your plants. You do need to maintain your pest control programme too, as the straw can act as a hiding place for lots of pests.
When you apply your straw, hoe the ground to open it up and remove any weeds first. Water the soil if it hasn't recently rained. I apply fertiliser and slug pellets to the ground before putting the straw down. Loosen the straw from
the bale and place around the plants, but don't push it hard against the stems.