Category Archives: Tips

Choose Your Garden Amendments Carefully

Are your fertilisers and soil amendments killing your plants? Click To Tweet

We have been growing a lemon tree from seed for a few years now and it’s getting pretty big but we nearly lost it, all because of some run-of-the mill, every day fertiliser. I hope our story will help you avoid the pitfalls of the fertiliser market.

This little lemon tree was doing pretty well until it started suffering from nutrient deficiencies
This little lemon tree was doing pretty well until it started suffering from nutrient deficiencies

As you can see by the yellow leaves in this photo, our lemon started suffering from one or more nutrient deficiencies (most likely nitrogen, iron and molybdenum). It started as just a general yellowing which we assumed was a results of reduced nitrogen uptake due to the cold weather (the pH of the potting mix was neutral and it really is too cold for citrus here but we’re giving it a go in our greenhouse because we really want fresh lemons) so I thought I’d follow the conventional wisdom and give it some nitrogen (just a little because it was winter) as well as the nutrients citrus most commonly lack (iron, magnesium and zinc) because if it was struggling to uptake nitrogen, chances are other deficiencies would show up soon and just a little bit of extra nutrient can help a plant along until the weather warms up.

We had some Epsom salts (for magnesium) but didn’t have an iron or zinc supplement so I purchased some iron chelate and a trace element mix (some people recommend putting a galvanised nail into the trunk of citrus trees to provide zinc but I don’t like the idea of damaging the plant that way and ours was way too little anyway so a trace element mix would provide zinc and all other nutrients the lemon would need.)

The instructions on the packet suggested adding an awful lot of both the iron chelate and the trace element mix so I started off with a half strength dose of those but the correct dose of Epsom salts. After a week or so of particularly cold weather, the plant started looking worse rather than better so I gave it another half strength dose of the iron and trace elements. The plant just kept getting worse though and developed blotchy chlorosis on some of the leaves and interveinal chlorosis on others.

Then I checked the pH of the potting mix. It was 5.5 which is too acidic for citrus. So I added some lime and monitored the situation. As the pH rose the plant started to look better so I kept fertilising the plant according to the instructions. Every time the pH dropped I added some more lime but the pH kept dropping and I couldn’t figure out why.  In the end we decided to replace some of the potting mix in case that was the culprit.

We bought some potting mix and checked it had a neutral pH then mixed in some soil from our chicken coop (for nitrogen) as well as a general purpose, organic fertiliser and some of the Epsom salts, iron chelate and trace elements as we figured this would give the lemon everything it needed. We then checked the pH again and it was down around 5 again. Clearly something we had added had changed the pH.

So we went through each additive to figure out what was acidifying the potting mix. The chicken soil and the fertiliser were pretty much neutral and the Epsom salts were only slightly acidic. The iron chelate dissolved in water had a pH of 5.5 however and the trace elements in water had a pH of less than 3! (that’s the lowest pH our probe will measure). So then we knew what was causing the pH to drop! I triple checked the packaging and there wasn’t any information on either pack to suggest that either the iron chelate or the trace elements mix would acidify the soil. I was very disappointed.

So we mixed up a new batch of potting mix with soil from the chicken coop and the organic fertiliser then replaced what we could of the potting mix in the lemon’s pot. I also checked the pH of our seaweed concentrate (it was thankfully neutral) and then watered the lemon in with a dilute solution to help settle the plant roots and boost the ‘immunity’ of the plant. We’ll be monitoring the lemon carefully over the coming months but hopefully that will solve the problem and it will green up soon.

The moral of the story is that you should always check the pH of the soil/potting mix around your plants regularly and especially when they’re looking unhealthy or when you’re applying any amendments. It’s also a good idea to check the pH of the amendments themselves just in case. It’s also worth noting that this sort of problem is much less likely to occur in an organic fertiliser because common organic amendments are pretty close to neutral the majority of the time.

Science in the Garden – Part 2

I recently wrote a post about an experiment that I conducted to determine whether liquid fertiliser improves the growth of plants growing in seed raising mix. If you missed it, check it out here.

Now the experiment didn’t stop there. When the seedlings grew too big for their pots (i.e. the roots were growing out of the bottom of the plants’ cells and were starting to resemble Repunzel’s famous long, golden locks) I transplanted them into bigger pots with potting mix that also claimed to have everything a plant needs to grow ‘big and strong’ and investigated the effect of liquid fertiliser on seedlings grown in potting mix.

As with the seed raising mix, liquid fertiliser improved the growth of seedlings grown in the potting mix; and it did so regardless of whether the seedlings received fertiliser when growing in seed raising mix. Seedlings that did not receive fertiliser when growing in seed raising mix (but then received some when transferred to potting mix) did not however grow as large or as healthy as seedlings that received fertiliser in both stages of the experiment. It thus seems clear that seedlings will grow best if given liquid fertiliser from the time they sprout onwards, even if the potting mix contains fertiliser. The most important time to give plants liquid fertiliser is during the early seedling stage when they're still in seed raising mix. Click To TweetInterestingly, the results of the experiment showed that it is more important to give seedlings liquid fertiliser during the early stages of growth when the seedlings are in seed raising mix. If plants are to be transferred to a garden (rather than kept in pots), it is likely based on these results that liquid fertiliser will continue to improve growth, though the extent to which this is true would depend on the properties of the soil – the poorer the soil, the greater the effect of the fertiliser. As long as you ensure young seedlings have the nutrients they need however, it seems that seedlings will still grow well without liquid fertiliser (provided the growing media has some nutrients) they just might not grow to their full potential.

Method

This second part of the experiment was slightly more complicated than the first. If I continued to fertilise the test seedlings and didn’t apply fertiliser to the control seedlings I wouldn’t know what effect the fertiliser in the potting mix would have had on the seedlings. The liquid fertiliser before transplant had a beneficial effect but after transplant how would I know whether any difference between the control and test seedlings was due to the continued application of liquid fertiliser or just left over from the initial applications of liquid fertiliser?

The answer was to create four types of seedling. The first type were seedlings that had not had any liquid fertiliser in the first phase of the experiment and didn’t get any fertiliser in the second phase either. These seedlings I labelled CC (control in phase 1 and control in phase 2). Half of the original control seedlings were put into this category but the other half I gave liquid fertiliser in phase 2 of the experiment and these I labelled CF (control phase 1 and fertilised in phase 2). Then I made the same split for the test samples from phase one. Half were not fertilised in phase 2 (these were labelled FC because they were fertilised in phase 1 but were not fertilised in phase 2) and the other half were fertilised in phase 2 (these I labelled FF because they received liquid fertiliser in both phases).

The results from this part of the experiment were likewise interesting.

Most seedlings responded to the new conditions and grew more than they had when they were in the seed raising mix. This may have been due to the fertiliser in the potting mix or it could have been due to the increase in root space – or a combination of the two. This would be something to investigate in future experiments.

Seedlings 3 months after the seeds were sown. The tray on the left contains seedlings that did not receive liquid fertiliser once the seedlings were potted up. The right hand tray holds the seedlings that did receive liquid fertiliser after the seedlings were transplanted into larger pots. There are four of each variety of plant. The two seedlings on the left in each grouping did not receive liquid fertiliser when they were in seed raising mix (those in the left hand tray are thus CC seedlings and those in the right hand tray are CF seedlings). The two seedlings on the right side of every group did receive liquid fertiliser when they were in seed raising mix (those in the left hand tray are thus FC seedlings and those in the right hand tray are FF seedlings). The varieties of seedlings in this photo are in order from left to right, top to bottom: lettuce, parsley, Brussels sprouts lettuce, summer savoury parsley, celtuce. The difference between seedlings that were grown in different conditions is most obvious in the celtuce seedlings because they grew to be the largest. The FF celtuce seedlings (far right) were the largest and greenest. The CC celtuce seedlings (3rd from the left in the left hand tray) were the smallest seedlings and were quite yellow - they clearly struggled a lot in this experiment. The FC seedlings (fourth from the left, in the left hand tray) were the second largest seedlings indicating that it is more important for seedlings to get off to a good start. They are a little yellow though, indicating that the seedlings were starting to struggle to get the nutrients they needed. The CF seedlings (third from the left in the right hand tray) were a little smaller than the FC seedlings but much larger than the CC seedlings indicating that it's not too late to start giving liquid fertiliser to seedlings when they're potted up but that seedlings not given liquid fertiliser when in seed raising mix will never quite catch up to those that were fertilised at that stage. The CF seedlings are however slightly greener than the FC seedlings indicating that while they got off to a slower start, they were getting the nutrients they needed in the second phase of the experiment and so they must still have developed a reasonable root system etc. This trend holds true for the other varieties of seedlings in this experiment with the exception of the brassicas, which seem to have been more variable in this experiment. Given that the brassicas grew lots of roots in adjacent punnets in phase one of the experiment, the observed variability may have been due to the roots being damaged on transplant (it was very difficult to remove the seedlings from their punnets without damaging the roots that were growing into adjacent cells).
Seedlings 3 months after the seeds were sown.
The tray on the left contains seedlings that did not receive liquid fertiliser once the seedlings were potted up. The right hand tray holds the seedlings that did receive liquid fertiliser after the seedlings were transplanted into larger pots.
There are four of each variety of plant. The two seedlings on the left in each grouping did not receive liquid fertiliser when they were in seed raising mix (those in the left hand tray are thus CC seedlings and those in the right hand tray are CF seedlings). The two seedlings on the right side of every group did receive liquid fertiliser when they were in seed raising mix (those in the left hand tray are thus FC seedlings and those in the right hand tray are FF seedlings).
The varieties of seedlings in this photo are in order from left to right, top to bottom:
lettuce, parsley, Brussels sprouts
lettuce, summer savoury
parsley, celtuce.
The difference between seedlings that were grown in different conditions is most obvious in the celtuce seedlings because they grew to be the largest. The FF celtuce seedlings (far right) were the largest and greenest. The CC celtuce seedlings (3rd from the left in the left hand tray) were the smallest seedlings and were quite yellow – they clearly struggled a lot in this experiment. The FC seedlings (fourth from the left, in the left hand tray) were the second largest seedlings indicating that it is more important for seedlings to get off to a good start. They are a little yellow though, indicating that the seedlings were starting to struggle to get the nutrients they needed. The CF seedlings (third from the left in the right hand tray) were a little smaller than the FC seedlings but much larger than the CC seedlings indicating that it’s not too late to start giving liquid fertiliser to seedlings when they’re potted up but that seedlings not given liquid fertiliser when in seed raising mix will never quite catch up to those that were fertilised at that stage. The CF seedlings are however slightly greener than the FC seedlings indicating that while they got off to a slower start, they were getting the nutrients they needed in the second phase of the experiment and so they must still have developed a reasonable root system etc.
This trend holds true for the other varieties of seedlings in this experiment with the exception of the brassicas, which seem to have been more variable in this experiment. Given that the brassicas grew lots of roots in adjacent punnets in phase one of the experiment, the observed variability may have been due to the roots being damaged on transplant (it was very difficult to remove the seedlings from their punnets without damaging the roots that were growing into adjacent cells).

Most varieties also continued to respond to the liquid fertiliser as there was a discernible difference between the FC and FF samples as well as between the CC and CF samples – the seedlings that were given liquid fertiliser when in potting mix were larger and healthier than the seedlings that didn’t get given liquid fertiliser at this stage even if they did receive liquid fertiliser when in the seed raising mix. This last point is an important one because it shows that if you diligently fertilise seedlings when they’re in seed raising mix but then neglect to fertilise them when they’re potted up, all your hard work can be undone.

Interestingly, there was quite a difference between the CF and FF seedlings as well. In conjunction with the above information, this indicates liquid fertiliser applied after seedlings are transplanted into potting mix doesn’t make up for a lack of fertiliser during the seed raising mix stage. So plants will grow better if they’re consistently given liquid fertiliser.

In many cases, the FC seedlings were also noticeably larger or healthier than the CF seedlings. This indicates that for some species at least, liquid fertiliser in the earlier stage of growth is more important than later on. This may be because the potting mix does contain more nutrient than seed raising mix or it could be because older and therefor larger seedlings have more roots and so are better able to take up nutrient where there isn’t much around. Or it could be because the healthier, more robust seedlings produced with the aid of early applications of liquid fertiliser are better able to grow with the head start they’ve been given even when they aren’t getting optimal levels of nutrients. Some of this is hard to test without specialised lab equipment but future experiments might be run in a similar way except with seedlings transplanted into larger pots of seed raising mix (then you can tell what effect the potting mix and the fertiliser within it is having on the seedlings).

So from this information, I conclude that seedlings grown in potting mix containing fertiliser will still generally benefit from the application of liquid fertiliser. It is however more important to ensure young seedlings are well fertilised as seedlings that get off to a good start will be healthier than seedlings that you try to

Future experiments could investigate different kinds of liquid fertiliser, application rates and different potting mixes to learn more about the optimal conditions for growing seedlings in containers.

Science in the Garden – Fertiliser Test – Part 1

As gardeners, we hear advice about every aspect of growing plants. On everything from irrigation to fertilisation to propagation to growing media, both modern science and ancient garden lore handed down from parents to children usually have something to say. Sometimes advice can be contradictory though and then of course there’s that tip your neighbour gave you last week that you can’t find in any of your gardening books but which he swears will give you the biggest crop of tomatoes you’ve ever grown. So, being a scientist, I spend no small amount of my free time researching whichever gardening topic has recently piqued my interest and when literature fails I do my own experiments. It is about one such experiment that I am writing today.

In this post I describe how I looked into the benefits of using liquid fertiliser on seedlings.  I wanted to learn whether the claims of fertiliser manufacturers are really true or whether they are just marketing hype designed to boost sales. Happily, my experiment clearly shows that applying liquid fertiliser to your seedlings will give you much bigger and healthier plants sooner. applying liquid fertiliser to your seedlings really will result in much bigger and healthier plants sooner Click To Tweet Interestingly, I also found that liquid fertiliser helps seedlings produce their first set of true leaves earlier too! Liquid fertiliser helps seedlings produce their first set of true leaves much earlier. Click To Tweet

Seedlings on the left were not fertilised. Seedlings on the right were given liquid fertiliser every week. What a difference!

When starting many plants from seed I sow my seeds in seed raising mix. When the resulting seedlings are large enough (or when they’ve had masses of root growing out of the bottom of their tray/punnet for a few weeks and I’m beginning to worry they will soon cover every surface within our greenhouse and then mount an invasion of epic proportions) I then transplant them into individual pots filled with potting mix. Now potting mix and seed raising mix suppliers often make claims about how wonderful their product is, how it will promote lush foliage and strong healthy roots and the fertiliser contained within (unless you buy the cheapest brand but even then, some still contain fertiliser) will fuel your plants’ growth for months to come. {No doubt the marketing people are descendent from those who started the rumour that eating your bread crusts would put hair on your chest (if you’re a boy) or make your hair curly (if you’re a girl).} But do these products really provide everything a plant needs (except for light and water and air of course)? If they do, why do some people feed their seedlings with liquid fertilisers? Have these people been duped by the marketing gurus that work for the liquid fertiliser companies? Have they been telling people the equivalent of ‘you won’t grow up big and strong if you don’t eat that pile of broccoli that I’ve mounded on the side of your plate’?

Well, I set out to determine for myself whether liquid fertiliser makes a difference to young seedlings.

To do this, I filled some seedling trays with seed raising mix, which claimed to contain everything needed to grow healthy plants from seed or cuttings. I then selected a range of seeds to sow, mostly edibles because that’s what I wanted to grow at the time. I then sowed the seeds at the right depth for each variety making sure to accurately record which varieties went where. For every tray, I then sowed another tray with the same seeds.The first became my ‘control’ tray which would not receive any liquid fertiliser. The duplicate tray would be my ‘test’ tray which would receive liquid fish emulsion and seaweed fertiliser once a week. I then placed the trays in plastic draws and poured in some water to keep the seed raising mix moist (the water wicks into the growing medium by capillary action). The whole lot then went into our greenhouse. Each pair of trays got the same amount of water at the same time (whenever they ran out). They were also placed next door to each other so they would get the same amount of sunlight. I also gave each tray identical doses of apple cider vinegar whenever they showed signs of growing algae (I can assure you this works well – possibly because the acidity prevents the algal growth or perhaps because the vinegar has antifungal and antibiotic properties – one day I’ll do a proper test to check whether this affects plant growth at all but my initial tests have shown no ill effects). Then I sat back and ‘watched the seeds grow’.

This first picture shows both the control and the test tray of seedlings after 13 days. The test tray which received fertiliser has seedlings that are just a little bigger than the control seedlings.
Seedlings 13 days after seed sowing. The tray on the left is the control tray (received no fertiliser) and the tray on the right is the ‘test’ tray (received fertiliser).
Seedling trays 20 days after seed sowing. Again, the tray on the left is the control tray and the tray on the right is the test tray. Notice that some of the seedlings that received fertiliser are distinctly larger than those that did not.
Seedlings 34 days after the seeds were sown. The seedlings on the right that received fertiliser are clearly larger than those on the left that did not. Some of the seedlings on the left are also looking quite yellow and are clearly unhappy.
Seedlings 34 days after the seeds were sown. The seedlings on the right that received fertiliser are clearly larger than those on the left that did not. Some of the seedlings on the left are also looking quite yellow and are clearly unhappy.
Seedlings 48 days after sowing the seeds. The seedlings that received fertiliser are very clearly larger than the seedlings that didn’t. (Some of the seedlings have also been transplanted into pots by this stage because they really were outgrowing their punnet).

As the various photos in this post show, most species grew better when they received liquid fertiliser. The liquid fertiliser produced either larger seedlings or healthier looking seedlings and in many cases, the liquid fertiliser promoted greater root growth. Interestingly, some species, particularly the brassicas, were more likely to spread roots into neighbouring seedling tray cells when they were given liquid fertiliser. Also worth a mention is the fact that liquid fertiliser seems to encourage seedlings to produce their first set of ‘true’ leaves earlier. For most seedlings, I waited until they grew their first set of true leaves before I started giving them liquid fertiliser. The parsley seedlings were much slower to grow though and because they were the only ones to not have their first set of true leaves after a couple of weeks, I started dosing them with liquid fertiliser when they still only had their seed leaves (it was just easier to fertiliser everything rather than skip those seedlings). To my surprise, the test parsley grew true leaves much sooner than the control parsley. This bears further investigation.

From this part of the experiment I conclude, at least for the species I tested, that it is a good idea to give liquid fertiliser to your seedlings when they are being grown in seed raising mix as it will produce healthier and/or more more mature seedlings in any given period of time. Future tests could investigate different types of fertiliser, various application frequencies and different brands of seed raising mix. It would also be interesting to see if air temperature affects the effectiveness (in winter for instance, when the temperature is lower, plants grow slower and generally uptake fewer nutrients so application of liquid fertiliser might have a greater effect if it makes it easier for plants to take up nutrients at a time when it is usually more difficult).

In my next blog post I’ll tell you all about what happened when I potted up the seedlings. In the mean time what do you think of liquid fertilisers? Do you use them in your garden? Do you think they serve a purpose not served by any other products? If you’ve never used liquid fertiliser in your garden, liquid seaweed extract is a great place to start learning as the benefits of liquid seaweed extract are many and varied.