Seed Starting at Rock Hill Orchard

In 2016, we started about 18,000 plants in our greenhouse at Rock Hill Orchard. We start all of our flowers, herbs, and almost all our vegetables in the greenhouse (the rest are direct planted in the field). By starting them early in the greenhouse, we can plan when they will be ready for picking as well as to better support multiple harvests. 

Our greenhouse is 24x48 and has both heating and cooling. Within the greenhouse are 4’x10’ benches built out of 2x4 lumber and wire mesh. The lumber provides the support, while the mesh actually holds up the plug trays so they can be easily pushed around and allows water to easily drain to the floor and outside via a long floor drain. 

We use plug trays to start everything. Over the winter, we create a spreadsheet of everything we want to start for the year, then there are formulas which start from the harvest date and count backwards to the transplant date, and seed date. The spreadsheet also tells us how many seeds to buy based upon the distance between each plant in the row. We grow about 20% more plants than needed to ensure that after germination and any other issues, we will have enough for each planting. 

We use primarily Dillen DPS50 plug tray inserts. These are very economical and can be reused. We then put them inside of 1020 flats which support the inserts. We are able to reuse the plug trays for several years. What happens is that as we are transplanting the plants, if the plugs don’t pop out, then the plug trays are damaged as the plants are removed. We wash the plug trays and flats with bleach before reusing them to ensure that there isn’t any harmful bacteria leftover from year to year. 

To fill the plug trays, we use Promix potting mix. This is a peat based product which is readily available and has enough fertilizer built-in to support the plants for a few weeks. 

Filling Plug Trays 
  • 1. Dump the Promix into a clean garbage can and break-it up so it is smooth. Use the hose to dampen the Promix. It should be damp, but not wet. It should just make a loose ball in your hand. Use a small shovel to turn it so that it is evenly wet. 
  • 2. Take a plug tray and put inside of a flat. We typically will setup about 30-50 trays at once. 
  • 3. Use a scoop to cover all the holes in the plug tray. Make sure that the corner holes are filled as well. Push down either with your fingers or by putting another tray on top and pushing down so that the mix is compacted, but not too hard. We want the mix to not be loose, but not loose the air within each plug. The reason for compaction is that when the plugs are removed, we want to make sure that the roots stay intact. But, if the plug is too hard, then the roots won’t be able to easily grow. The mix should be about ¼” below the top of the tray. 
  • 4. Use a dibble board or a pencil or your fingers to push down inside the middle of each plug so there is a depression of about ¼” (note this will change depending upon how deep the seed needs to be placed. 
  • 5. Plant your seeds. We used to plant two seeds in each hole, but that led to having to thin all the plants, so we found it was easiest just to plant extra seeds in another flat and then when needed just to transplant as needed between plug trays. 
  • 6. We use an EZ Seeder to plant our seeds. This saves us a lot of time as planting small seeds is a very slow process without any kind of automation. Planting the trays by hand is perfectly acceptable and is what we did for years until we realized how many hours we were spending putting in the seeds. 
  • 7. After seeding, lightly coat the tray with a layer of vermiculite. Note that some seeds require light so this step would be skipped for them. 
  • 8. Use a mister to water the flats the first time. The mister is used instead of a hose as the water from the hose might wash the seeds away! 

In the greenhouse, we have several benches (tables) that have propagation mats on them. The mats are called RediHeat from Phytotronics and allow the flats to be warmed to a particular temperature. By heating the soil within the flats, the seeds will germinate faster and more evenly. Once the temperature outside gets warm in May or June, we stop using the mats as the temperature in the greenhouse is the same temperature as the mats (or warmer).  Sometimes we put plastic covers over each plug tray as this keeps the humidity up which makes the seeds sprout faster. 

Once the seeds sprout, the trays are removed from the heat mats as if they stay on the mats after sprouting, they will quickly grow leggy (tall and tin). From this point forward, the trays are watered automatically each day via overhead sprinklers. The greenhouse can automatically water based upon times of day different sections. 

We primarily use natural light for growing. We do have a small number of greenhouse LED lights which allow the lights to be placed a few feet above the plants. The reason that you provide additional light close to each plant as that will promote growth of the plant without the plant growing tall and thin trying to find the light. 

When it is time to transplant the trays, they need to be “hardened off”. This is a process over several days where we put the plug trays outside during the day, then bring them back inside at night. This starts the transition process for the plants so they are more ready to be transplanted to a colder environment than that which they were used to.
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