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YOUR GARDENING QUESTIONS

Do houseplants cause damp?

The stories about the houseplant heroes (August 2021) made me wonder if it’s healthy to have hundreds of plants inside. Wouldn’t there be so much condensation that it’s likely that mould would grow?

SARAH WELLS, AUCKLAND

To be comfortable and healthy we need the humidity levels in our homes to be in the Goldilocks zone – not too high or too low but just right.

If humidity levels are high – over 55 per cent for long periods – there’ll be condensation problems and mould will thrive. On the other hand, low humidity (under 30 per cent) has its own set of problems – dry skin, flyaway hair, and itchy sore eyes. The mucous membrane lining the nasal passages dries out leading to nose bleeds and there’s an increased chance of colds, flu and other infections as viruses survive longer in dry conditions. And it’s not just living things that don’t appreciate low humidity – paint cracks, wooden furniture dries out and floorboards warp.

Plants also need the right levels of humidity to thrive. Plants do indeed add moisture to the air through transpiration. Water from the soil travels through the stems to the leaves and evaporates out of small pores in the leaves called stomata. But humidity loving plants also absorb moisture through their leaves. Large leafy plants including peace lilies, spider plants, golden pothos, philodendrons, rubber plants and palms are the ones likely to affect humidity levels. Many of them have also been found to purify the air. Plants with low water needs and lower transpiration rates, such as succulents, aloes and cacti are said to reduce humidity.

The amount of water transpired by an individual plant is negligible so a few plants in a room are unlikely to have any noticeable effect on humidity levels. Even with hundreds of plants in an small enclosed space, the total effect will contribute less moisture to the air than a steamy shower or a boiling pasta pot.

Ventilation is the best way to keep humidity levels

“in the zone’’ so open the windows to allow the air to circulate. If the air feels comfortable for you, it will be right for your houseplants as well.

Barbara Smith

Strange tomato

I wondered why this tomato sitting in my fruit bowl at room temperature was looking a bit lumpy. Then it sprouted all around the top. I’ve never seen anything like it before. MARGARET PAVITT, KAIAPOI

This is an example of vivipary, when seeds still attached to a fruit germinate. It’s quite common in tomatoes grown in glasshouses in winter. It is related to uneven temperatures (ie a cool spell after some warmer weather followed by more warm days) and day length. The trusses of tomatoes closest to the windows of the glasshouse are more likely to be affected as that’s where the temperatures are more variable.

Vivipary also occurs in strawberries which is easily seen as the seeds are attached to the surface of the fruit.

Some flowers can show vivipary too. In warm, damp conditions hollyhock seeds can germinate within flowers still attached to the stem. In some irises and lilies, little bulblets germinate in the axils where leaves join the stems. Barbara Smith

Passion killer

My plant survived winter and a move, but it’s not liking our new place. It’s been infested and looks sick. Is there a natural way to get rid of these bugs? I prefer not to use sprays.

SAGA VIGRE BOHINEN, AUCKLAND

Passionfruit are temperamental. In the right spot, they’ll thrive and grow like weeds but if something is not to their liking they’ll succumb to all manner of pests and diseases.

Does the plant’s new position have all the conditions it needs to thrive? North facing, sunny, frost free, freedraining soil, adequate moisture but not too much? Passionfruit hate wet feet.

The silvery patches are signs of infestation by thrips – spray with Yates Success Ultra. If you’d rather not spray, plant a new passionfruit plant, well away from where the current one is.

It would be a good idea to start a new plant anyway, even if you decide to keep the existing one. Passionfruit only live for four to five years in ideal conditions so it’s a good idea to have a replacement plant coming along.

Barbara Smith

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en-nz

2021-09-01T07:00:00.0000000Z

2021-09-01T07:00:00.0000000Z

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