SO Gardening — January 12


SO Gardening — January 12

Sunday, January 12, 2020

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Dear Orchid Doc:

What are the drawbacks of growing orchids in peat?


Dear Kay-Ann:

If you have a heavy hand with the watering can, you need to be careful when growing in a peat mixture. Because the medium stays moist longer you need to be careful not to overwater. Wait until the top inch of the medium is dry. If you're not sure, wait another day or two. Many orchid lovers find that the Phalaenopsis grown in peat requires watering only half as much as plants grown in bark.

Peat is lightweight, especially when dry. We find that our specimen plants, with long flower spikes and heavy blossoms, tend to become top-heavy. Unfortunately, our top-heavy specimen plants tip over when they're in lightweight peat, in lightweight plastic pots. Between the light medium and the light pot there isn't enough weight to keep a plant upright. So when plants are specimen-sized we move them into heavy clay pots.

Dear Orchid Doc:

How much humidity do orchids need?

Orchid lover

Dear Orchid Lover:

Phalaenopsis orchids enjoy 50% humidity. If your home is dry because of winter heat or summer air conditioning place a small humidifier near, or a humidity/pebble tray under your plants to maintain optimum humidity. Grouping plants together will also help maintain humidity around your plants.

Dear Orchid Doc:

What would cause the petals and sepals on one of my phalaenopsises to stick together and not open fully?


Dear Mildred:

Assuming that this is a plant that has flowered normally before, there are several possible causes. Atmospheric dryness can prevent normal opening. It can be a passing anomalous blooming, or it can be genetic. It could also be that the plant is exuding sap and the sticky material is causing the flower parts to stick.

Dear Orchid Doc:

Can you tell me what the secretions are that some orchid plants put out around the stems of their flowers? Sometimes it is sticky and develops sooty mould like on Grammatophyllum scriptum. On other orchids, such as Oncidium Sharry Baby, it is more watery. I find it seems to appear in the morning.


Dear Tessa

The secretion is simply plant sap, called honeydew, which is secreted by healthy plants. It is as you note, basically sugar water, and can lead to sooty mould. This is why sooty mould can often be an indicator of sucking insects, which feed on this same sap, supplied to them by the plant's osmotic pressure. When the pressure is sufficiently high, the sap passes right through the bugs' digestive systems, resulting in conditions favourable for sooty mould.

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