Half-Price Quadgrow Fertilizer - Update

 To forget how to dig the earth and tend to the soil is to forget ourselves - Mahatma Gandhi

In this post, I suggested the possibility of saving a few pounds on fertlizer costs (Nutrigold) by using a more dilute solution; i.e. half-strength soluble fertilizer solution. Part of the logic behind such a move is that with the Quadgrow system, the plants are grown in a medium (in my case, coir but other options are available) that will soak up and store nutrients not used immediately by the plants.

I added an update to my previous post, noting that while the aubergines, bell peppers and tomatoes were doing just fine on the 50% nutrient solution, the cucumbers appeared to be under some stress. By way of demonstration, here is an aubergine fruit picked yesterday (21/8/26) - Photo 1 - that weighed in at 666 grams. Typically, my home-grown aubergine fruits come in around the 200 - 350 g weight.

Photo 1: 666 g Aubergine (21/8/26) vs Satsuma!

The important question is whether the cucumbers have 'suffered' from a reduced nutrient regime. In past years, it has been normal for the cucumber plants to 'burn themselves out' early as each plant produces 40+ cucumbers. The summer of 2026 will probably be the hottest on record, comfortably beating the previous record in 2025! Temperatures in the polytunnel regularly exceeded 40 ℃ which puts added stress on the plants. Fortunately, the Quadgrow system maintains a constant and sufficient water supply to the plants which certainly helps. However, large-leaved plants such as cucumbers have greater rates of transpiration so tend to be stressed somewhat easier.

In Figures 1-3, I have plotted the daily mean, low and high humidities for the past three summers (June, July, August) in descending time order (i,e, 2026 - 2024). Highest humidities occur overnight as the temperature drops (often reaching amaximum around dawn) whereas lowest humidities are found during the late afternoon when temperatures are hottest.

Summer 2024 (Figure 3) was a 'normal' summer followed by a very hot summer (2025, Figure 2) and an even hotter summer (2026, Figure 1). It can be observed that the number of low humidity/high transpiration events (i.e. high plant stress situations) is greatest in 2026, followed by 2025 then 2024. Note that these humidity values were measured close to, but outside, the polytunnel. Low humidity extremes should be greater and more numerous in the polytunnel itself.

Figure 1: Mean, High & Low Daily Humidities (Summer 2026)

Figure 2: Mean, High & Low Daily Humidities (Summer 2025)

Figure 3: Mean, High & Low Daily Humidities (Summer 2024)

Consequently, in hindsight, this year was not the best time to start an experiment on reducing nutrient supply to the plants! Which is why I recommend a more prudent approach to reducing nutrient costs in the future; alternate between full and half doses to start with (25% cost savings) and, if everything goes well, reduce nutrient loading further.