2019 ASHS Annual Conference

The mature size of half-high and low-bush blueberries is more suitable in hydroponic greenhouse production than high-bush varieties. In fall 2018, Vaccinium angustifolium ‘Brunswick’ (BW) and Vaccinium corymbosum x angustifolium ‘Northland’ (NL) cuttings were rooted for 66 days under intermittent mist in substrates compatible with hydroponics systems. Cuttings were stuck in rockwool cubes (RC), shredded rockwool (SR), cococoir (CO), or 3 perlite:1 sphagnum peat moss (v/v; PP). Weekly fertilizer applications of distilled water, 75 ppm N from 16-4-17 OASIS® hydroponic fertilizer or ChemGro three-bag hydroponic fertilizer, were made; all were adjusted to pH 4.0. Each treatment combination was replicated 6 times with 6 cutting subsamples per experimental unit (e.u.); N=432 cuttings for each cultivar. Percent rooting was calculated per e.u., and rooting quality was evaluated using a 6-point visual scale (0 = dead or no callus, 1 = callus, 2 = few roots, 5 = many roots). Electrical conductivity and pH of rooting substrates were measured on pour-through samples collected at final harvest. Cuttings from NL had substantially better rooting percentage (63%) and rooting rating (2.5±1.5) compared to BW (17.8% and 1.3±0.8, respectively). Rooting percentage for both cultivars was lower in the two rockwool substrates (SR at 21.8% and RC at 15.2%) compared to PP and CO (61.6% and 64.4%, respectively). The fertilizer treatments did not affect the rooting rating; EC across treatments ranged from 0.4 to 0.6 dS/m. Both RW and SR resulted in higher pH (7.2±0.2 and 7.1±0.1, respectively) compared to PP and CO (5.5±0.5 and 6.2±0.2). The rooting ratings for these treatments followed a similar pattern: SR was 1.3±0.5, RC was 1.1±0.4, PP was 2.7±1.0, and CO was 2.4±1. Because blueberries prefer acidic substrates, the PP and CO substrates provided more ideal rooting conditions. There was no benefit to applying low rates of fertilizer during propagation. The municipal water used to mist the cuttings had an unbuffered pH of 8.8, therefore the influence of the substrate on altering the pH appeared to influence rooting results.