Containers are a popular and versatile way to grow flowers in gardens, but as the nutrients in growing media start to run out after around six weeks, additional feeding is required to produce healthy plants with abundant flowers. There are several ways to feed containerised plants, including liquid feeds, slow/controlled release fertiliser granules, and foliar feeds.

Foliar feeding provides quick, short-term delivery of plant foods, with plants absorbing nutrients through their leaves. The value of this technique has been explored in commercial horticulture and cut flower production, but very little is known about how this type of feeding affects nectar and pollen production, and subsequent bee visitation.

As part of our new trial in partnership with Hozelock, we will be exploring whether foliar feeding can improve flowering and nectar and pollen provision for bumblebees. We will be feeding nasturtiums weekly using Hozelock’s Pure sprayer, which has been designed for applying naturally derived and homemade recipes in domestic gardens. Some of our plants will be fed with comfrey, others with seaweed, and as a control, a third group will be sprayed with water.

We have chosen to test comfrey and seaweed liquids because both are naturally derived, can be obtained from environmentally sustainable sources and are popular with organic gardeners.

Comfrey
Russian comfrey (Symphytum x uplandicum), most notably the variety ‘Bocking 14’ has long, searching roots which are able draw nutrients up from deep in the subsoil. The lush foliage is rich in the primary plant nutrients (nitrogen, phosphorus and particularly potassium), as well as other elements and compounds important for healthy growth. Potassium is vital to plants which are at the stage of forming flowers and setting fruit, so comfrey liquid is commonly used to feed plants like containerised tomatoes. Comfrey also bears wonderful flowers for bees and is one of the plants included in the Blooms for Bees border.

The leaves of comfrey are harvested by gardeners and can be used in a variety of ways. For consistency in our trial, we’ll be using Agralan comfrey tonic, but it’s very easy to make your own liquid comfrey feed.

Seaweed
Seaweed has long been used by gardeners as a fertiliser and soil improver in a similar way to comfrey. It contains primary plant nutrients, as well as magnesium and various trace elements which promote healthy growth.

There is no public right to collect seaweed from beaches, so most gardeners do not have access to a ready supply, but there are dried and liquidised forms available to purchase. For this trial, we will be using Chase seaweed extract.