Conservatory and House Plants

We probably use the term Conservatory Plants a bit too freely – after all, plants were around long before conservatories, and with a bit of ingenuity and research, it is amazing the number of plants you can grow in sun-lounge, porch or gently heated greenhouse. Many smaller plants can be accommodated, and will positively relish on a sunny or shady position in the house. And some, with a bit of care, can be grown outdoors in milder gardens. With several layers of fleece I have kept Plumbagos, Jasmine azoricum and several other plants outdoors in our Suffolk garden, even during the 2017/18 winter, when temperatures dropped to minus 7 or lower.    

It is an unfortunate fact that many conservatories, especially the smaller modern designs, are far too hot, poorly ventilated and inadequately shaded in summer for most plants, as well as people. Such conservatories really come into their own during autumn to spring, providing the light levels are good, and the temperature is kept above freezing. On the other hand, a conservatory with a northerly aspect will be beneficial for many shade-loving plants (and humans) in the summer.

Aquiring a New Conservatory

If you are in the happy position of planning the building of a new conservatory consider very carefully it’s position, and ensure that you can provide generous ventilation, at ground level to allow cool air to enter, and in the roof to allow hot air to escape. Make sure this is of a type, in terms of security, which you are happy to leave open when you are out of the house. Blinds (preferably of the external variety, which prevent excess heat from entering in the first place) are essential for sunny conservatories.

Large Conservatories

If you are lucky enough have a large conservatory, there are plenty of plants which will respond eagerly to the space and protection that such a structure can provide, and it is worth seeking out plants which are difficult to accommodate otherwise. 

Small Conservatories

Even a small conservatory or frost-free greenhouse or sunroom allows a far wider range of plants to be grown than an unheated structure, and many will reach their full potential by growing and flowering much better and longer, as opposed to merely surviving at lower temperatures.

Care during the Summer

Many tender plants can be bedded out like Pelargoniums, or plunged in their pots into beds and borders for the summer, at the end of which they are then cut or trimmed back, tidied up and put in a dryish frost-free position for the winter.

Plants (like people) will benefit from a spell outside during the hottest part of the summer, remember a conservatory or anywhere else indoors is not a natural environment for plants. Not only does this relieve them from heat stress, but also exposes them to the wind, which makes for sturdier growth. Additionally, any pests will be less comfortable, and may get picked off by birds.

Temperature

We give a minimum temperature as a guide for most plants, but other factors should be taken into account: for example a plant may survive a short sharp frost, but may succumb to a long period of slight frost. Also, a plant kept on the dry side will survive where others in wetter conditions will perish. And finally, a mature plant will survive significantly lower temperatures than a young specimen. Where we give a temperature, it should be regarded as a minimum - plants will generally be happier and look better if kept a few degrees warmer. However, too high a temperature combined with low winter light levels encourages weak spindly growth which will be prone to pests and diseases. Plants that are naturally deciduous will be better off being kept fairly dry and cool. We thoroughly recommend the purchase of a thermometer, digital or otherwise, to monitor the temperature. The lowest reading will often be just before dawn outdoors, and in a lean to conservatory this may be more noticeable as any benefit of central heating will have dropped away too. 

Heights

Sizes are given as an indication, but this is a difficult area: for example a Passionflower that is capable of growing 50ft or more may flower quite happily in a large pot at a mere 5ft! In general the heights we give relate to plants grown in a border or very large container. A smaller container will reduce the height and vigour of the plant. To keep such plants healthy, an annual top-dressing of compost and fertiliser is necessary, and regular watering and feeding through the growing season will be required.

Potting & Composts

On aquiring a new plant, the temptation is to pot it on (i.e. put it in a larger pot) straight away. A better plan is to allow the plant to acclimatise to its new surroundings for a week or so. There is a possibility that it might drop its leaves as a response to a change in e.g. humidity, in which case it should have minimal watering until new leaves are formed. Wilted leaves can be a sign of over watering, as well as under watering, so lift the pot to check its weight, or probe the compost to see how wet it is, and act accordingly. A plant with few or no leaves cannot transpire away excess water, leaving this moisture in the compost, which can then exacerbate the problem.

As a general rule, tender plants don't need potting after late July to early August - few plants will die through not being potted on. but some may very well succumb in the winter if the roots are surrounded by an excess of cold damp compost. If in doubt, don't pot on!

Avoid the temptation of putting a plant in a much larger pot - using pots and inch or two bigger all round is usually sufficient. Citrus and Passiflora need special care in this respect.

With regard to compost, a mix of John Innes no. 3 and some peat based compost will be fine for most plants; grit, composted bark, or garden compost can be added if available. The coarser material ensures good drainage, whilst the organic matter will provide water retention. Succulents relish a good helping of grit (10 mm pea shingle will do).