Fall Greenhouse Management

September 18, 2023

Let’s suppose that you are growing tomatoes in your greenhouse next year. You’ve had disease and fruit fill challenges this past season. What can you do to set yourself up for a successful upcoming season?

A soil test is always a good place to start when thinking about how to manage for next year. All nutrients are critical, but from a soil perspective, calcium, magnesium, potassium, phosphorus, and nitrogen are especially critical because they are needed in large amounts. Calcium and magnesium balance is needed to maintain a healthy soil structure, and along with potassium, are also responsible for proper pH balance.

Sulfur and sodium tend to accumulate in greenhouse soils because natural rainfall doesn’t leach them out; and especially so if the soil doesn’t have the right calcium to magnesium ratio. It is necessary to balance the sodium to proper levels; otherwise, the sodium will reduce potassium uptake and create fruit fill challenges. High pH can also cause fruit fill challenges.

Let’s suppose that you have both high sodium and high pH, and that the high pH is coming primarily because of excessive magnesium or potassium. You have also had challenges with Timber rot or other soil borne fungal diseases, such as verticillium wilt, fusarium wilt, etc. Following is a good recovery program for soils like this:

  • Start with a soil test before this program so that you have a baseline with which to work from;
  • Apply Aragonite or finely ground gypsum to help flocculate the soil and help sulfur and sodium move out of the soil;
  • Apply sulfur (up to 50 lbs. per 1000 sq. ft.);
  • Subsoil every twelve inches to allow the water and roots to penetrate deeper;
  • Use light tillage if needed to level the ground;
  • Spread cover crop seed mix. The mix should include oats, mustard, and peas minimum. Mustard helps reduce soil borne fungal pathogens. Oats release calcium and phosphorus. Peas build nitrogen. Bulbing crops can be added as these scavenge potassium and release them again when decaying. Look for all-winter kill cover crops. Buckwheat can be added to help acidify the soil. Go heavy with the mix. And let’s add an invitation to be innovative with the mix – add some phacelia, flax, safflower, etc.
  • Add a thin layer of oats straw to protect the soil surface. Make it thick enough to break the impact of water and prevent soil surface crusting, and thin enough to allow the cover crop to germinate afterwards;
  • Sprinkle irrigate 12-20 inches of GOOD water to leach out excess sulfur and sodium;
  • Inject the Rejuvenate program to stimulate rapid bacterial and fungal activity in the soil. Recommended rates per 1000 sq. ft. for intense crops like this are 1 qt. Rejuvenate, 1 qt. SeaShield, ½ ounce Santerra. Other potential biologicals to include are Bio-Digester, which promotes rapid carbon breakdown into organic matter; and Spectrum DS, which contains sodium digesting bacteria;
  • The greenhouse should be open and potentially even have the covers removed;
  • Ensure that the cover crop has enough nutrients to grow properly. Nitrogen is especially important after the heavy sulfur application, but foliar feeding should also be considered.
  • After the crop has winter-killed, inject another application of the Rejuvenate program;
  • Let the soil rest, but keep it moist. When soil dries out, it will start to lock up potassium. If you have potassium problems, it is critical to keep the soil moist all winter and keep the biology thriving.

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Source: Melvin Fisher | Sponsored by Keystone Bio-Ag LLC