Top tomato tips

By Jim McColl

Published:

LOOKING through the Beechgrove glasshouses the other day, I was struck by the number of different types of tomato being grown. At the last count we had seedlings coming on of about 20 different varieties. The reason is that my colleague Carole Baxter is going to take a look at some of the new kinds that are on offer, concentrating to a degree on bush types.

How are they to be grown? Whilst it may be true that we are being subjected to a bit of global warming, I can’t be confident about advising people to grow tomatoes out of doors in these parts. Now you may detect a note of caution in that statement and you would be right. If there is one thing I have learned in this business – you can’t afford to be dogmatic, well, most of the time.

As soon as you say this can be done or can’t be done, someone somewhere will pop up to prove you wrong. In the present context, I know there are people in this area who happen to have a fine microclimate coupled with the right kind of soil and that enables them to grow bush tomatoes outdoors successfully most years.

Our bush tomato observation will be planted in a polytunnel.

How will they be grown? I reckon we will probably have some growing in the soil and others in growbags. Planting them directly into the soil is by far the simplest, so long as there are no soil-borne diseases present. Commercial tomato crops were grown in this manner for decades but each winter the soil was sterilised (pasteurised really) to kill off pest and disease organisms. When that process started to become too expensive, some growers turned to grafting their plants on to rootstocks that showed resistance to these various problems. I believe some people still do that.

The particular problems I have in mind are various types of eelworm and wilts.

My view has been, look after the soil, grow the crop well and continue to use the technique until the first signs of disease finally appear – be optimistic, it could be years before that happens.

It hasn’t happened to me yet but as time goes on, I feel that the odds are shortening. For more than 10 years, I have grown tomatoes in the same greenhouse soil.

The trick I use is to plant into a bottomless pot, sitting on top of the soil and filled with multipurpose compost. When the roots have outgrown that, they penetrate the border soil underneath to find more water and sustenance. In preparation, that soil has been turned over, incorporating plenty homemade compost, lime if required and then a dressing of all purpose compost. The great advantage of this system is that the compost in the pot warms up quickly, immediately encouraging the roots into vigorous growth.

By far the most popular method of growing tomatoes nowadays must be in growbags, although I have no statistics to prove that.

Let me remind you again – buy the bags in good time and warm them up before planting. The major problem that people seem to have with this system is watering.

From not being able to supply enough water to satisfy the vigorous early growth in the earlier stages, the problem is exacerbated by the lengthening days when plants are subject to long hours of good light during which time they are “sweating profusely” and need to take in lots of liquid.

If you have the time to be very attentive during this period that’s OK, the problems arise when people are away from home for long hours each day.

As the season advances, the situation goes in to reverse, the growbags become saturated and despite slitting the sides to allow excess moisture to drain away, the compost remains saturated and the roots are starved of oxygen – they start to drown.

In my view the problem is that growbags are the wrong shape. Instead of being pillow-shaped, they should be shaped more like a shoebox. In other words, the ends should be square, the height being the same dimension as the width.

That would make drainage much better.

I’m not the only one to hold this view. To overcome the problem, I’ve seen some people prop the growbags on their side, some will split a growbag across the middle, standing the two halves on end and some will tip the growbag compost out into big pots.

Each option will increase the vertical height of the container so improving drainage. Give gravity a chance. Finally, on this topic last year I did see someone lay one growbag on top of the other, with matching pieces cut out top and bottom.

Whatever variation of the traditional method you choose to follow, can I remind you that there is much to be gained by feeding at every watering?

Begin using quarter strength feed then as the plant grows away, move to half strength, being prepared to vary it as you gauge the health and productivity of the plants.

Unless you have a heated glasshouse, you should not be planning to set plants out before the second week in May and even then keep an eye on these night temperatures. Tomatoes don’t like temperatures below 10C and if the light is good during the day, they would prefer a night minimum of 15C.

The main message is give yourself plenty time to have everything ready.

QUESTION TIME

I’ve just planted a birch sapling, it is about two metres high. What would happen if I take the top off it?

The answer is that it will change the eventual shape of the tree. Some people will want to do this because they think the plant is going to grow too tall so why didn’t they buy something smaller in the first place?

Many birches will grow tall and straight because the top bud on the stem is said to have apical dominance, that is to say it has an in-built mechanism that keeps it heading for the sky.

Cut off the head and it and it will certainly be more mop-headed than narrowly conical but when you see our native birches, they exhibit a wide variety of shapes anyway.

In principle, taking the leading shoot out of any plant tends to make it produce a wider crown with numerous shoots. Quite often the new shape will be equally as pleasing but then, you just have to wait and see.