We custom mix all of our potting soil at One Straw Farm. This ensures that nursery starts receive the proper growing conditions and organic nutrients during their time in pots and succeed in the garden after being transplanted. Most commercial greenhouses start with a basic potting mix, with very little fertility, and then fertigate the plants during their growth cycle. Those plants may look greener and healthier than some of our starts, but they are often fragile and get shocked when planting into garden soil. It often takes time for the plants to adjust to the actual soil found in most gardens.
Our goal is to provide all of the nutrients the young plants need in the potting mix, to develop healthy root systems and balanced plant growth, so that when plants are transplanted into the soil, they continue to grow vigorously and don’t suffer from transplant shock. Of course, many other factors are involved in whether plants will thrive in the garden, including soil fertility and tilth, water, whether the plant roots are “bound” in the pot because they were grown too long, plants getting burned by too much sun initially, etc. We use the same starts we sell to customers at One Straw Farm for the produce we grow for sale at the farmers market, and can attest to their quality and ease of transition from pot to bountiful crop.
The secret to our successful soil mix is compost, specifically, worm castings produced at the farm. Every scrap of leftover vegetable waste from our kitchen and from the farm goes into our pile of red worms that turn that unwanted debris into “black gold”. Almost every batch of soil mix produced at One Straw Farm gets a large portion of our worm castings. To the worm castings we add peat moss, vermiculite, perlite, a little bit of farm soil and a couple of scoops of a special mixture of organic minerals and fertilizers we call “fertility mix”. The quantity of each ingredient varies, depending on the nutrient needs of the crop and its growth stage. Our fertility mix is comprised of mostly greensand, seaweed meal and alfalfa meal, with smaller quantities of bat guano, blood meal, bone meal, trace minerals and humates. We find that the correct proportions of all these ingredients creates a well-balance mix suitable for most of the crops we grow for transplanting.
Proper timing and pot size is also critical to a successful plant in the garden. Most of our nursery starts are planted in succession, to ensure that customers will be able to purchase plants that are sized up perfectly. Vigorous plants like tomatoes are grown in 4” pots. This allows the plant to fill in the horizontal space between plants in addition to growing vertically. Our goal is to have a tomato plant that has extensive root growth that matches above-ground growth, rather than a tall, leggy tomato plant that is unable to support itself on transplanting day.
Our lettuce plugs are grown with a similar goal. Instead of selling giant lettuce starts that look beautiful but will not really grow any bigger once transplanted, we sell head lettuce starts that are about 30 days old and have just barely filled their cells. Transplanting at that stage of growth means that the lettuce can be grown to a full-size head, and it will generally keep growing at the same rate as it grew in the trays. This is exactly the same method we use at the farm, when we transplant about 1,000 baby lettuces each week into the field for sale as full-size heads 5-6 weeks later.