Sunday, July 6, 2008

Bottom Watering for Soil Blocks

Many people are convinced the only way to raise soil blocks is by bottom watering. This is also known as manual ebb and flow, static evaporation, and water wicking. It is not the only way to water soil blocks, but it is the best way to water if you have very little time to monitor your seedling garden. Let's explain bottom watering and explore the variety of methods used with advantages and disadvantages, and instructions on creating them.
Bottom watering is the manual watering technique that fills a shallow, water tight tray with water up to a predetermined height of water at specific intervals to hydrate the roots of seedlings, transplants, or cuttings. The rate at which water is supplied is determined by the rate of evaporation of the environment, and root wicking caused by plant growth. The amount of water supplied is determined by the size of the plant container (or soil block) and the depth of the holding tray or water reservoir. Bottom watering can be done manually by watering cans, or automated by timers outfitted with drip irrigation, or with timers on pumps which fill and empty the reservoir, known in the hydroponic industry as ebb and flow (E&F).
You should ask yourself, "Do I need to bottom water?". "Am I at work for 4-8 hours a day, every day?" "Am I new to soil blocks and gardening?". "Do I have A LOT going on in my life and tend to forget little things?". "Am I going on vacation, or away for the weekend?". "Do I live in the desert?". "Do I want to grow baby greens?". If you answered "Yes" to any of these questions, then you are a bottom watering candidate!
After viewing a brief discourse on soil block making at my website:, you'll want to have your system of watering prepared in advance of making blocks, since they will need somewhere to go right away. Big Tip Here: If you are bottom watering, you need to make absolute sure that your blocks are very firm. Make sure and charge the blocker 3-4 times and watch for water oozing out the tops. If not, your blocks could just melt away.
The fastest and easiest way to start bottom watering is to reuse some of your recyclable containers. Look for aseptic packs, or rice dream and soy milk containers, Styrofoam take out trays, salad bar trays with clear lids, plastic bottle bottoms, old cake pans, salad green tubs, etc. Make your blocks and discharge them into the container with about 1/8" spacing between the blocks. After you seed or place cuttings, you won't have to water for about three days, as the newly wet blocks contain enough moisture in them for that time. Cover your seeds with plastic to make absolute sure they won't dry out. After about three days, you'll want to water your blocks by gently pouring in water on the side of the container, never directly on the block, to a maximum of 2/3's of the height of your chosen block, be it micro, mini, or maxi. You'll have to watch and keep track of how fast it is evaporating and how fast your plant uptakes the water in order to gauge how often you'll be filling your trays up to the 2/3's mark. Never go over that line or you could drown your seedling. Better to have too little water at this stage then too much as the block itself contains a lot of water pores for emergency use. Only when the plant is well established in the block could it be over watered and pose no threat to growth. If your block is made from a potting soil that DOES NOT CONTAIN FERTILIZER OR AMENDMENTS, make sure to begin an organic fertilizer program in 10-14 days until your blocks are transplanted into your garden bed. Consult my web site for fertilizers to use, or my past blogs at for free ideas.
The next best way to begin bottom watering is to cut the bottom out of an old Rubbermaid tub, provided at least 2" of the bottom is salvageable. A jig saw is easiest! Try cutting the bottoms out of any old plastic junk lying around. This works well for a larger blocking system.
The best way for larger scale growing is to make a custom tray out of plywood for the bottom, and 1x3's or 1x2's nailed or screwed around the sides to make a lip. Then, take a spare or old piece of greenhouse plastic (4-6mm) and line the tray and make it water tight. Be sure and sand any sharp edges and wrap it completely and staple, duct tape, or lathe it to the bottom of the plywood. If you decide to staple, use some kind of a tab on top of the plastic to prevent it from tearing, as the water will stretch out the plastic and make it loose if you don't secure it firmly. This method takes a little longer to construct, about a half an hour to an hour, depending on your size and if you have to rip your lumber down to size, but creates a solid tray that can be used for a few years. Build shelves for them in a greenhouse, or create a potting block bench top with the option to cover with wire hoops (9 gauge) and plastic for a hoop-bench propagation station! Add a large heat mat with a thermostatically controlled switch and you got yourself a mini greenhouse.
Now, you can take the last option and create a hydroponic system known as the ebb and flow with a pump and timer. For this you will need: a timer(capable of multi-settings), a little fountain pump, a water reservoir or Rubbermaid tub, silicone, some plastic tubing that fits your pump, and whatever fittings secures the pump with the tubing with couplings. Now, build your plywood trays deeper, at least 2" for the micros or minis, or 4" for the maxis. Drill a hole the same size as your tubing at a corner of the tray and then cover with plastic. That hole will be your drain and fill hole. As you position your tray make sure it is slightly slanted towards the hole for proper drainage. Position the tray on a bench over the reservoir and secure the pump in the reservoir, silicon the tubing to the hole in the plastic lined tray. Check for proper water drainage and tilt. Hook up the pump to a timer, fill the reservoir with water, and manually test to see how long it takes to fill up the tray to the 2/3's rule on whatever block you choose. This amount of time will be programmed into your timer to come on once every three times a day. Next, fill with soil blocks, and seed or transplant or fill with cuttings and wait three days and turn your timer on. The water should fill through the pump and drain through the same hole. Mix fertilizer in your water at the 10-14 day mark and watch for rapid growth in order to transplant before the roots spread out too far. You can transplant or pot on the next block and replace them back in the tray, or get them out in the garden. Make sure to harden plants off properly to prevent stunting of growth.
Experiment and create for yourself the wonderful options of bottom watering. Be sure to check out timeless, in-depth and hot information at my website to steer you clear of soil stumbling blocks. And, be sure to stay focused on blog spot to receive the three part series on hydroponic soil block gardening. I'm sure it will please those who want to go hydro, but need to stay with organic soil systems.

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