Soil conditions for 'better dahlias'by Walter Jack
How good is the soil in your dahlia patch?
If you want to prolong flowering, have quality blooms and good healthy clumps of tubers then you must have your soil in good order.
When you dig your dahlias, dig a clump, hold it by the stem and tap the stem two or three times. If the soil falls away easily even in wet conditions, you know your soil is in good condition. Another guide is that clumps should be of a good size and tubers clean and healthy in appearance. Action should be taken if soil is difficult to remove from the clumps or if the tubers are small, discoloured or look unhealthy. Such tubers are not good keepers.
The soil conditioner "Gypsum" is a great way to free up your soil. I like to apply "Gypsum" each spring. It is a natural mineral mix of calcium sulphate that loosens clay and compacted soils allowing air and water to penetrate.
If on digging, your tubers are discoloured and have poor keeping qualities, then you should consider a dressing of lime at least one month prior to planting. Do not overdo the lime as dahlias prefer a slightly acidic PH. I usually apply a dressing of lime every second year only. Pea straw spread over the beds for the winter then dug or rotary hoed in is a good source of nutrients for your dahlias and is also great in assisting in breaking down clay and poor soils.Once you get the soil in good condition your dahlias will have stronger growth, good soil also allows fertilisers to do their job.
You may wish to try the following: "Gypsum" 1 to 3 kgs per square metre. For real clay compacted oils use the heavy rate. 1 kg will normally give good results. "Lime" 1 kg to 3 to 4 square metres. "Nitrophoska Blue Special" (12% nitrogen, 5% phosphorus, 14% potassium, 6% sulphur plus trace elements. 50grams per square metre, best applied 1-2 weeks prior to planting. Apply a side dressing around mid January. (Do not overdo "Nitrophoska". Apply carefully, too much will give robust growth with few blooms.) "Sulphate of Potash" one handful around each plant, approximately mid January. Apply around the bush, not against the stems or foliage as it will burn. Soluble Potash applied through a watering can is a quick fix for sagging weak stems. Results can be seen as quickly as 5-7 days. Do not use Muriate of Potash as this causes the stems to become very brittle.
Gypsum, Nitrophoska Blue Special and Sulphate of Potash and Soluble Potash are much cheaper to purchase at a farmer's fertiliser outlet. Gypsum comes in 25kg bags. Get a few growers interested and bulk purchase. You will save. The same products at a garden shop are usually more expensive.