Keeping Things Green in the Greenhouse

With this wonderful summer heat we are having, your greenhouse plants should be growing by leaps and bounds.

Once the mercury passes above 25, a lot of Yukoners seem to say, “It’s too hot for me.”

Inside the greenhouse, however, where the temperature can go to 30 or more, the plants thrive when given enough water and ventilation.

Water is one of the trickier aspects of greenhouse gardening: too much water and the roots will rot; too little water and the plants will wilt and, without immediate corrective measures, will eventually die.

Realize that under our lovely, hot summer conditions that what your greenhouse plants will need is water (and plenty of it).

I see way too many greenhouses where plants are under-watered, especially if we get a prolonged hot spell.

Plants can absorb water both through the roots and the leaves, so misting along with regular watering is one way to adequately supply your plants with needed moisture and will help cool down a greenhouse.

There are several ways to check for adequate moisture. If you have waist-high growing benches and adequate drainage holes as you water the plants, you should start seeing water drip through the bottom of the benches. When it does, you have added enough water.

Another way to check for adequate moisture is to simply dig into the soil for a few inches and physically feel the soil to see if it is moist at that level. A third method is to simply get a moisture thermometer with which you can easily probe the moisture content of different locations in your greenhouse.

In our own greenhouse, we relied heavily on the “drip” method: if water dripped adequately enough out of the bottom of the benches, the plants were deemed to have an adequate drink.

Misting the plants can raise the humidity of a greenhouse and also cool down the greenhouse during those extreme midday temperatures. Misting in conjunction with adequate ventilation can lower the midday heat stress of your plants.

Keep in mind though that the ideal soil temperature of most greenhouse crops is 16 to 18. That’s soil temperature!

The frequency of watering is another mystery to many and is difficult to answer because every situation is different.

The size and location play a part in watering in your greenhouse.

Add to that the type of plant and container used (in benches, in the ground and everything in-between) and that adds to the confusion.

If you are growing some plants in hanging baskets, in the greenhouse, others in benches and others in raised beds, there will be different frequencies of watering.

The only reliable method is to physically check the moisture content of the soil. A hanging basket or a tomato plant, grown in a pot, will need more-frequent watering than plants grown in a bench.

Plants can talk to you …

Learn to “listen” by spending time in the greenhouse observing the plants and assessing their needs. Are the leaves showing signs of wilting? Then it’s high time to water. Is the soil dry on the surface? What about five inches down? Does the plant generally look healthy?

All of these clues help access what the plant is trying to tell you.

A 30-degree temperature in the greenhouse is not necessarily a bad thing if you provide adequate moisture through lots of watering and/or misting and proper ventilation.

Ingrid Wilcox operates Lubbock Garden and Floral Consultant and offers gardening, greenhouse and flower arranging workshops. Contact her at [email protected]

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