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Choosing an automated self-watering regime


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When you've set up your Harvst mini greenhouse, what should you choose for the self watering program? There's no definitive answer, as self watering / self irrigation depends so much on what you're growing and the time of year, but there are some broad guidelines we can give.

You have a number of settings which can be set differently for each of the zones in the greenhouse:

  • How long to run the pump (in seconds).
  • Two timer schedules, varying from twice every day (high summer) to once every 5 days (winter).
  • Watering hold (don't water) when the soil is already wet.
  • Extra water when the soil has gone dry.
  • Extra water when the weather has been particularly hot for more than 3 hours.

How long to water for?

For each of your two self-watering zones, you can choose how long the pump runs for. You don't need to run the pump for long to get a fair bit of water into your soil. Some plants prefer a good drenching from time to time, and other plants prefer little and often. Research your particular plants needs, and make sure you experiment with the pump time before you plant (or move the plants out) so you don't waterlog your seeds and seedlings.

Ensure you pump enough water to give the soil a good soak; what you don't want to do it just wet the top level, as the roots won't get water and your plants won't do as well.

Different experts have different opinions on whether it's best to water in the morning, the evening, when it's hot, or not ... so do your reading and make your choice when it comes to choosing a time of day to water. Something to consider for solar powered systems is that you'll be guaranteed to have the best pump pressure (due to battery voltage) from midday onwards in winter, and any time of day in summer.

Non-heated greenhouses - winter / early spring

In the winter, we find that self watering on a timer once every few days is often enough. Soil just doesn't dry out that fast in the cold weather. When the odd bright, sunny day comes along, your greenhouse will get warm, the plants will be thirstier and the soil will dry out faster, but there's little risk of them wilting. If you like, you can add "water when soil is dry" too - but set it low, perhaps around moisture level 2. A more important setting is the "don't water when wet" as you don't want to waterlog your plants. Once you know the wet level of your soil (see our other post on learning about soil moisture sensing), you can set the "don't water above" to the wet moisture point of your particular soil.

Heated greenhouses - winter / early spring

Heated greenhouses are a bit different, as plants will be growing faster, using more water, and moisture will be evaporating faster from the soil. Heated seed trays can actually dry out in just a day if they are warm, so we recommend auto-watering more regularly. Start by watering for a few seconds once every other day and see how your soil is doing. For seed trays, where the soil dries faster and the plants are more vulnerable, definitely use the "water when dry" option.

All greenhouses - summer self watering

Automatic watering really comes into its own when the weather warms up. As spring moves into summer, you'll want to increase your watering from once every few days to once a day, and even twice a day for thirsty plants. Make use of the guard rails of "water when dry" and "don't water when wet", to deal with the large variance in water needs due to the difference between hot sunny days and cool overcast days.

What do YOU do?

We're keen to hear from you about what you're doing, and how well it's working for you (or not). Share your successes and failures and we'll all learn how to grow more!

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