With the cooler spring temperatures this year, we decided to cover a few hop hills with row-cover to see if it would advance the hop plants in the OMAF and MRA Herb Demonstration Garden at the Simcoe Research Station.

Applying row-cover is a regular practice in other crops, such as strawberries, as a method of frost protection and to reduce the number of days to fruiting during cool spring seasons.  Row-cover typically provides a 1-2^oC increase in overnight temperatures compared to no row-cover; however, depending on the weight (thickness) of the row-cover, some studies suggest a difference as high as 6^oC.  Daytime temperatures underneath row-cover can be much higher and care must be taken in order to prevent heat stress or heat damage to the crop during warm and sunny spring days.

In this demonstration, row cover was applied to two different hop cultivars (Nugget and Willamette) on April 12 and removed on April 30, 2013.  Photos 1, 2 and 3 show the hop growth stages of the plants prior to, and after, row-cover treatments.

Photo 1: Nugget hops on 30 April, 2013, no row-cover applied.

Photo 2: Nugget hops on 30 April, 2013, with row-cover applied.

Photo 3: Willamette hops on 30 April, 2013: foreground with row-cover, background without row-cover.

On the hills without row-cover treatments, both varieties were still in the principal growth stage 0, ‘Sprouting’.  On the hills that had row-cover treatments, the plants were in principal growth stage 1, ‘Leaf Development’ (stage 12 to 13: 2^nd to 3rd pair of leaves unfolded).

On April 30, the Nugget plants without row-cover had 2 shoots per plant approximately 31cm tall whereas the plants ‘treated’ with row-cover had 12 shoots, approximately 28 cm tall.  The untreated Willamette plants had 4 main shoots at 10 cm tall and treated plants had 9 main shoots 14 cm tall.

So, from this un-replicated demo, it appears that row cover may have a benefit in advancing hop growth in Ontario; however, there are a few things to consider and evaluate:

1. This demo was un-replicated and should be evaluated in a replicated experiment.
2. Applying row-cover earlier in the season than what we applied (e.g. in late March or early April) may increase the soil temperature and therefore increase shoot initiation earlier in the season.
3. Hops can grow remarkably fast during the growing season.  Applying row cover may increase early growth but untreated plants may catch up during the remainder of the season.  Following the plants through harvest would provide the bigger picture to see if there is a significant increase in yield to determine if the costs of purchasing and applying row cover are worth the additional effort and expense.  Row-cover treatments may also potentially provide a cultural management practice for growers in cooler areas of Ontario to advance hop growth in regular seasons.

This row-cover demonstration was simply looking at applying a cultural management practice widely used in other crops to see if it would be beneficial to hops in Ontario.  We hope to evaluate this practice in future years to determine if there is a benefit to hop growers by increasing yields or advancing the crop in cool growing seasons or different growing zones across the province.