Here’s a useful easy tip:
When seeds germinate they often come through with their seed shell still attached to the seed leaves.
A propagator with lid helps because it keeps the air humid and prevent the seed shells from drying out.
If the lid is kept on too long, the extra moisture makes the seedlings leggy – especially the first ones through. A dropper or pipette (as above) will help individual seedlings discard their seed shells.
A New Product On The Market
A new product that makes watering and feeding tomato plants in grow bags easier is the “Hozelock Grow Bag Waterer 2810”. Thanks Steve for mentioning it in the comments last week!
It has a reservoir of 15 litres of water and uses capillary action/matting to draw the water into the grow bag through spiked holes in the bottom. A water level indicator and a hose attachment makes this waterer a very useful addition to growing tomatoes in a grow bags.
They are available on Amazon for around £20.00.
If asked would I buy one, the answer is yes. Although the 15 litre reservoir is a bit small, there is a hose pipe attachment that could easily be used with an auto watering timer if away on holiday.
A similar system is the Quadgrow Planter that also uses capillary matting but with pots over a reservoir. It’s twice as expensive as the Hozelock but contains four pots and a 30 litre reservoir.
The advantage of any system where plants can absorb water at their own rate, and where water is always available is huge.
Money Saving Option
Of course for those who enjoy a bit of DIY, there are less expensive options.
On a recent trip to Poundland (it’s amazing what you can get for a £1.00!), I spotted a row of black storage boxes. They were next to the tools so I think they’re meant for hammers and nails etc. However, they will make great water reservoirs being light-proof and although plastic, quite strong when the lid is on.
Here’s one idea …
All that’s needed is a slot cut in the lid of each container for a strip of capillary matting. This would then go up through a cut in the grow bag. These containers are 14 litres each. No need to ask the price!
Under-bed plastic storage boxes make good low level reservoirs but it’s best to line them with black plastic to make them light-proof. Algae and other growth can be an issue where there is water, nitrogen and light.
Leaf Stomata & Foliar Spraying
Plants are like humans in as much that they have pores.
In plants the pores are called stomata and are mainly on the underside of leaves.
The stomata are used to release water vapour. As water is lost out of the leaves, water is drawn in through the roots.
Because water molecules tend to stick together, this acts as a chain from the roots to the leaves from where the water evaporates. This process is called transpiration.
Stomata also open to allow carbon dioxide into the leaves which is essential for photosynthesis – the process by which plants make their own food (sugars). Commercial greenhouses add extra carbon dioxide to the air so that plants will grow faster.
Stomata also release oxygen which is very important for us!
The stomata open and close depending on weather conditions.
When it is sunny and bright, they open to release water vapour in order to draw up water and nutrients through their roots and allow more carbon dioxide into the leaves.
Of course if leaves release too much moisture the plant wilts. If they keep their stomata closed they won’t be able to absorb carbon dioxide and that will slow growth – it’s a continual compromise.
A plant can easily become stressed if the water supply at its roots is erratic as this will affect transpiration which includes nutrient take up. A good reason to have a reservoir for the grow bag!
Stress can cause so many other issues including, blossom drop and smaller ripe fruit than expected.
Guard Cells – The Doors of the Stomata
Each stoma (singular) in the leaf has a guard cell on either side that opens and closes. They look a bit like bananas and sausages!
The guard cells open and close by pressure – as water (including sugars etc.) is pumped into the guard cells they open the stomata (3), as pressure is reduced they close (lower photo).
This is good, because on a hot day if a plant runs low on water, the guard cells close (less pressure) and prevent more water from escaping from the leaves. Eventually, if the plant is not watered it wilts to the point of no return as the pressure within it is lost. The guard cells will be closed at this stage trying to conserve as much moisture as possible.
Top photo open – bottom photo closed.
How This Relates To My Plants
Because most stomata (pores) are found on the underside of the leaves, it is best to foliar spray the underside of the leaves. Moisture and nutrient absorption into a plant’s system is also quickest through the underside of the leaves because of the many stomata and the cuticle (outer waxy layer) is much thinner than on the upper surface.
Spraying the upper leaf surface takes longer for nutrients to enter a plant’s system because of the thick waxy layer. However, it has been shown that nutrients are absorbed to the same amount over time (top and bottom leaf surfaces), just not at the same rate.
The problem with spraying the upper leaf surface is the danger of fungal spores landing on the leaves. Blight spores are totally harmless on a dry leaf – that’s worth remembering!
Interruption of Water Flow
Spraying leaves regularly (everyday) is not a good idea because every time a leaf is wet, the release of water vapour from the stomata slows because moisture (humidity) outside the leaf is greater than the moisture inside – making it harder for leaves to release water vapour.
This interrupts the flow of nutrients from the roots. Excessive foliar spraying could lead to deficiency of the immobile elements such as calcium and therefore cause Blossom End Rot. A foliar spray once every three or four days is the most often I would spray.
Foliar spraying/feeding is best used as a supplement – when leaves show a nutrient deficiency. Or at a time in a plant’s growth when more of a particular nutrient is needed and a deficiency is more likely to occur.
A build-up of nutrients on the leaf surface can also cause leaf damage and make further foliar spraying less effective.
- Spray the underside of leaves for quickest results
- Wet leaves are vulnerable to blight
- Spraying too often may interrupt nutrient supply from roots and cause BER
- Use as a supplemental feed
- Too much foliar feeding can damage leaf surfaces
Next week … how to tell the difference between nutrient deficiencies when leaves show the same symptoms.
I hope you’ve enjoyed the technical part of this newsletter. There is plenty of information out there on the internet. My aim is to try and join some of the dots and make a little of it relevant to tomato plants.
Please leave comments as usual in the section below – it was great to hear from so many people last week!
Tomato seeds take about six or seven days to germinate in the airing cupboard.
Using a small seed tray makes it a lot easier to find a warm place – a plastic food container is ideal.
It’s very important to move seedlings as soon as they germinate into a light position to stop them from becoming leggy.
Keep the seed compost dryish – seedlings need very little water and are prone to diseases that are encouraged by wet cold soil and roots.