Primrose monitoring example

Primrose 10.5cm potted wk 38 2021

We used Candy Vanilla from Rudy Raes, we knew it was a hungry variety

Peat free compost (coir & wood fibre) compared to standard peat & wood fibre (January SAP results)

Grown cool vent setpoint 10C Heating 1C

Grown in shuttles for 6-8 weeks then spaced out onto bench with capillary matting

Water from borehole with nitric acid dosing, conductivity 800 uS/cm, we use a continuous low-level feed 3-400 uS/cm 15-5-30 at ever watering.



The primroses had been spaced, the foliage covered the pot and looked healthy enough, however, the SAP result showed that there were some deficiencies. The weather was cold with some overnight frosts and mainly dull. The compost was fairly wet so we couldn’t hand water them. We applied 2 lots of bio 20 as a fairly coarse spray 7 days apart at 1500 uS/cm.


We could now see chlorosis in the leaves of some varieties, that are prone to it, Mojito for instance. The weather was cold with very little sunshine. the compost was still fairly wet so we applied 3x bio 20 at 2500 uS/cm. By the end of the month, we could see the chlorosis was disappearing in the varieties that show it. At the end of December, the temperatures picked up dramatically going from 2C to 14C in one day. The Candy Vanilla was still looking okay and was in bud by the end of December


The SAP results showed we had improved the nutrients and now we were thinking temperatures had played a part in the Chlorosis, when it is very cold the compost temperature can be much lower than the leaf temperature, perhaps the roots couldn’t supply the leaves. The Vanilla now looked much greener and started to flower in January.

Peat free results over the 3 months with a standard compost in January

primrose vanilla peat free
peat freepeat freepeat freepeat
NovemberDecemberJanuary peat freeJanuary peatPeat free difference
nitrate n13520020013268
ammonia n13520020013268

From the SAP results, we could see some differences between peat and peat-free so we had a look at the roots.

Primrose Vanilla Comparison

Both batches of primrose vanilla have received the same soluble fertiliser and foliar regime.

The top row is standard peat/wood fibre compost, The lower row is peat-free coir/wood fibre mix

This is the standard peat/wood fibre compost

This is the peat-free, it seems to have a different root development, with very little root development near the top


Both batches of vanilla looked the same visually and flowered at the same time, however, we have noticed a fair proportion of blind plants in the peat-free batch and none in the standard compost